Cutting The Grass

Guest Post by Willis Eschenbach

Sufi stories of the wisdom of the foolish Mulla Nasrudin have been around for a thousand years or more. One of them tells how the Mulla was walking down the street one day. Three stories above him, a man was working on a roof. The workman slipped and fell. He landed on the Mulla. Fortunately, the workman was totally unharmed. The Mulla, however, was injured enough that he had to be taken to the local hospital to recover.

When the Mulla’s disciples came in to see him, they asked him what lesson could be learned from the incident.

“Shun reliance on theoretical questions,” said Nasrudin, “questions like, if a man falls three stories from a roof, will he have to go to the hospital?”.


With that as prologue, in the Americas both North and South we have birds called “turkey vultures”, Cathartes aura. Where I grew up they were known as “buzzards”. In parts of the South they are known as a “carrion crow”. I’ve always felt a kinship with them because back in the 1800’s my great-grandfather, The Captain, named his tugboat the “Carencro” after the local name for buzzards.

Plus buzzards have a very important job. They’re the garbagemen, the cleanup crew for all the corpsicles left behind by nature, our allegedly loving mother nature who is also famously “red in tooth and claw” … you go, Mom. Here’s a turkey vulture eating a dead armadillo somewhere down south.

turkey vulture II

The buzzards visit our place a lot, but fortunately, not to eat. We live in a hillside clearing in a redwood forest. It’s the place with the tiny house icon, to the right of and above the center in the photo below. Because there are no trees, the cleared area around our house is warmer than the surrounding forest. This warm air rises.


The buzzards know about warm air rising, of course, because those jokers hate to flap their wings. They are champion gliders, going for mile after mile without ever flexing their wings. In their search for free rides, they regularly use the warm air off of our clearing to work their way up to the ridgetop behind us. They’ll come in and wheel round and round, gaining altitude with each pass Once they’ve gotten high enough on the warm air rising from our clearing, they drift off majestically along the ridge, in their perpetual search for the dead.

Here’s the curious part. A few days ago while I was working outside, I noticed that the buzzards were coming in over the clearing as usual.

But they weren’t gaining the altitude that they were expecting to gain. They weren’t able to get their usual lift. I watched as bird after bird tried their usual route without much success. One even had to flap his wings to get out of the top corner of the clearing. For a buzzard, that’s a sure sign of failure.

Finally, one buzzard ended up gliding so close to the ground that it couldn’t even make it over our eight-foot (2+ metre) deer fence. It flared out its wings, gained a little altitude, and settled on one of the wooden fence posts. This almost never happens. Nothing to attract them here.

turkey vulture

All of this set me to pondering. Why were the buzzards getting fooled about the amount of lift? What had changed?

The only thing I could think of that had changed was that the previous day I’d had the grass cut. I couldn’t cut it earlier because of the endless rain. By the time I got back from Fiji, the grass had gotten up to about chest high in parts. Literally. Chest high.

But that explanation didn’t seem right to me. I’d always figured that if you had a grassy field, it kept the surface from getting too hot. And if there was no vegetation, like in the desert or on the beach, the surface would get hot. As computer modelers like to say, it’s just “simple physics” …

But if that were so … why were the buzzards getting fooled? I love the natural world for exactly this kind of puzzle.

My conclusion was that I was looking at the wrong metric. The issue for the buzzards was not how hot the surface got. It was how hot the air got … and that’s a very different question. The sun heats the surface, and the surface heats the air. So a big issue is not how hot the surface gets, but how well the surface acts as a heat exchanger. Here are the two surfaces in question, mowed and unmowed.

cut grass albedo

It seems to me that the field of grass on the right side of the photo is a pretty good sun –> surface –> air heat exchanger. The grass slows down the passage of the air over the surface, allowing it to be warmed. This warm air will then rise into the free atmosphere. The grass also increases the amount of surface area exposed to the air by orders of magnitude. Finally, the grass acts as a pretty good solar trap, where the solar energy goes in but not much is reflected back out.

Regardless of the explanation, I cannot deny that I expected that cutting the grass would increase the surface warmth and thus the lift for the buzzards. However, the buzzards proved me 100% wrong.

Now, suppose we were trying to model this on the computer. This is far below the size of a single gridcell in a climate model. So it would have to be “parameterized”, meaning that we’d put in numbers that we think are reasonable for this kind of a change … but that’s just putting numbers to a theory about what will happen.

Which brings me back to Nasruddin and the issue of relying on theoretical questions, like “If a field of tall grass is mowed, will the buzzards fly higher or lower?”.

In this case, to my surprise, the answer was “lower”. Which is how I found myself looking into the eye of a buzzard sitting on my fence post. Oh, I didn’t stare at him. That kind of reckless eyeballing makes any wild creature nervous. So I looked at him in glances and pauses, and generally pretended that I didn’t see him.

Now, the birds circling so low to the ground had attracted two cats to the action. And when the buzzard landed on the fence post, the neighbor’s cat crept slowly over to the base of the buzzard’s post. The buzzard paid little attention until the cat was directly below him (her?). Then they both froze, with the cat looking straight up along the post at the buzzard looking down, and the buzzard looking straight down between its toes at the cat looking up.

Our cat just sat and watched them both. I watched all of them.

Then some other poor sucker of a buzzard came in, and he couldn’t get enough lift either. As a result, he came right past the ear of the buzzard on the post. Startled, the post sitter took off. The two cats both immediately vanished into hiding.

Me? I laughed and shook my head at the wondrous intricacies of the climate, and I went back to work.

Best of the springtime to everyone,


PS—Perhaps the most intriguing part of the experience to me was the exquisite judgment of the buzzards as to how much lift they could expect off of our clearing. Birds are quite surprising in their ability to learn. And in that vein, after avoiding the clearing for a couple of days, today for the first time I saw a buzzard come through. However, it didn’t push its luck, and it didn’t get close to the ground. The buzzard just came in, got the main lift from the center of the clearing, and wheeled back out again. What a world, amazingly intelligent beings on all sides.

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May 22, 2017 9:24 am

Magpies are the smartest.
Despite their reptilian brain, lacking a neocortex, they are able to recognize themselves in a mirror, just like us great apes.

Reply to  Gabro
May 22, 2017 9:30 am

our dog looks at the reflection in the mirror and knows right away that it is not looking at a dog. humans and birds on the other hand cannot tell the difference. who exactly has the superior brain?

Reply to  ferdberple
May 22, 2017 9:43 am

Link to sources on that?

Reply to  ferdberple
May 22, 2017 9:53 am

ferd….depends on the bird..some birds definitely do

Reply to  ferdberple
May 22, 2017 9:56 am

If true, I’d suggest the dog relies more on other senses (probably sound and scent). Because the mirror neither sounds nor smells like a dog, other animal, or intruder, it’s not interesting.

Reply to  ferdberple
May 22, 2017 10:10 am

Actually few animals are smart enough to understand that they are seeing themselves since it requires at least a rudimentary self-awareness. Some, but far from all, primates can do it, and a few birds particularly in the crow family.

Reply to  ferdberple
May 22, 2017 10:13 am

Willis Eschenbach May 22, 2017 at 9:51 am

… I know right away that I am not looking at a dog …

maybe or, not even, an old sea-dog? 😛

Reply to  ferdberple
May 22, 2017 10:19 am

Yup, crow family. Among mammals, also reportedly elephants and dolphins.
I’ve read that ants also pass the mirror mark test. Their brains are tiny, but so are their bodies.

Samuel C Cogar
Reply to  ferdberple
May 22, 2017 10:33 am

Now don’t you all get too carried away with your claims about “reflection recognition” or lack thereof, ….. by individual animals of the different terrestrial species ……. and best you keep in mind that most every individual animal of said species has to have a “drink of water” every now and then ……. and there is a good possibility that 10% to 30% of times that the animal bends its head down to get a “drink of water” it will see its own reflection on the surface of the water. And I’m sure those animal learn to recognize their own “reflection”, otherwise they would be frightened and run/fly away only to die of thirst.

Tom in Florida
Reply to  ferdberple
May 22, 2017 10:48 am

When I look in the mirror I recognize my grandfather looking back. My brain and eyes still see the world as I did when I was 30, the reflection brings me back to the reality of aging.

Reply to  ferdberple
May 22, 2017 11:17 am

“And I’m sure those animal learn to recognize their own “reflection”, otherwise they would be frightened and run/fly away only to die of thirst.”
I’ve seen quite a few birds of several species trying to fight it out with shiny hub caps and rear-view mirrors. You think they had managed to do without drinking all their lives?

Reply to  ferdberple
May 22, 2017 11:42 am

For a month now, a goldfinch has been attacking its reflection in my kitchen window. Dunno if it’s trying to fight or mate, since their plumage, to me at least, is the same in both sexes.
I wish it could learn to stop wasting precious calories in this way. I might have to cover up the window.

Don K
Reply to  ferdberple
May 22, 2017 1:29 pm

“our dog looks at the reflection in the mirror and knows right away that it is not looking at a dog”
Varies from dog to dog. Some of ours ignore their reflections in either mirrors or the glass door onto the deck. Others have regarded their image with deep suspicion. One was prone to attack the dog in the mirror — which was, of course, all too willing to fight back.

John F. Hultquist
Reply to  ferdberple
May 22, 2017 2:20 pm

You might like this — a Turkey attacks an F-350:
Tom sees Tom and fight ensues

Reply to  ferdberple
May 22, 2017 2:52 pm

The ability to recognize oneself in a mirror is called having a theory of mind.
Few animals possess one.
Child development experts are very interested in the stage of human growth that a child first learns to be able to recognize such things…because it goes hand in hand with other changes in perception.

Reply to  ferdberple
May 22, 2017 2:57 pm

I should say instead, having the ability to recognize oneself in a mirror is one aspect of a theory of mind.
And since experiments can be designed, such as the magpie one above, to determine if an individual creature can recognize oneself, this is one way to ascertain something which might otherwise be difficult to know.

Reply to  ferdberple
May 22, 2017 3:03 pm

As anyone who has raised a baby knows, up to a certain point in time, a young child thinks that if she closes her eyes, you cannot see her.
This is the stage that the game peek-a-boo is funny and interesting to the child.
IIRC-Once they can recognize themselves in a mirror, they no longer think that you cannot see them when they close their eyes…they know that this only happens if you close YOUR eyes.
And they lose all interest in peek-a-boo.

Reply to  ferdberple
May 22, 2017 5:03 pm

Depends on the dog. Ours sees its reflection in a glass door, thinks there is a trespassing dog outside. Then I appear next to the trespasser. Confusing. There are many dogs, but pretty sure there is only one of my pet human, and he’s standing next to me. How does he do that? Must be smarter than I thought.

Tom Billings
Reply to  ferdberple
May 22, 2017 6:24 pm

The dog knows it isn’t another dog, because he cannot *smell* another dog. Smell is far more crucial to dogs than to humans.

Don K
Reply to  ferdberple
May 23, 2017 12:59 am

MC – “Must be smarter than I thought.”
I’m pretty sure the possibility that I might have a brain in my head has never been entertained by any of our dogs. I think they spend a lot of time wondering how anyone as stupid and incompetent as I could possibly have been able to rise to a position of leadership in the pack.

Samuel C Cogar
Reply to  ferdberple
May 23, 2017 6:11 am

I’ve seen quite a few birds of several species trying to fight it out with shiny hub caps and rear-view mirrors.

YUP, and during mating season a bull moose will sometimes attempt to fight it out with a railroad locomotive.

Reply to  ferdberple
May 23, 2017 10:09 am

Idunno – sometimes humans don’t seem to get it quite right either.

george e. smith
Reply to  ferdberple
May 23, 2017 7:50 pm

Howcome the chap in the mirror is left to right bass ackwards, but not up and downwards ??
People want to know these things.

Reply to  Gabro
May 22, 2017 3:38 pm

Parrots, despite their intelligence, apparently don’t recognize themselves in mirrors.
I’ve seen them look behind the mirror, in trying to figure out what’s going on.

Reply to  Gabro
May 23, 2017 5:49 am

After keeping a few chickens for awhile, I have been amazed by how much more active and interesting they are than I expected. They come running when I call the pig in since they know they will be fed. Even with clipped wings, they are flying a bit and roosting in pretty high places at night. And they are much more the hunter than I ever knew. They remind me of little velociraptors as they hunt for insects and the occasional lizard.

Reply to  billw1984
May 23, 2017 10:07 am

Yup, you’d not want to be around a hungry 6′ chicken – and they’re always hungry.
The various movie raptors obviously were modeled on chickens, especially they way they run. They should have been modeled on turkeys in both size and shape as well as intelligence.

May 22, 2017 9:27 am

very interesting counter-intuitive observation. the cut grass likely gets warmer than the uncut grass, because it is not exchanging heat with the air as efficiently. but we would assume that the warmer cut grass is heating the air more – but observation shows it is not.
thus, the conventional wisdom about the effects of land clearing may be completely wrong. they may only be considering land temperatures, without factoring in the efficiency of heat transfer to the air. radiation versus conduction and convection.

Reply to  ferdberple
May 22, 2017 3:55 pm

Perhaps the heat being transferred also lofted quite a bit of water vapor (transpiration) thereby making the rising air more dense and capable of providing more lift.

Reply to  Rocketscientist
May 22, 2017 5:06 pm

water vapour lowers air density.

Keith J
Reply to  Rocketscientist
May 22, 2017 6:49 pm

Water vapor is buoyant so it lowers density but its signature is a cumulus cloud overhead. Glider pilots recognize thermals from clouds and soar from cloud to cloud, making sure to stay below the cloud deck.
What goes up must come down so when there are thermals, there are also sinks. I proffer the buzzards in the story were trapped in a sink where they had expected thermals. It happens to the best of pilots who may be forced into outfield landings. With prevailing winds, thermals and sinks both deviate from vertical and most likely, there are winds aloft. Bird brains have issues with change and the unmowed ground was just the change forcing their outfield landing. Lucky for them a radio call and derigging- trailering mea culpa isn’t required.

Reply to  ferdberple
May 22, 2017 4:02 pm

Does green vegetation absorb more of the red end of the spectrum? One might think so from the fact that it reflects green light and above.
A vertically arranged densely packed absorber to capture more of the heat might be just the ticket…um like a field of grass?

Rick Lafford
Reply to  ferdberple
May 23, 2017 5:49 am

Actually what may be going on is that the tall grass tends to hold the warming air against the surface for a longer time, allowing it to become much warmer – and buoyant – than it would otherwise. Once Willis cut the tall grass down the surface available to hold the air was decreased and the result was that the air didn’t have time enough to warm sufficiently to lift a buzzard before tearing away from the grass and rising. I have no idea what the sink rate of a buzzard is in still air but the lift would have to be greater than that to support the bird. Buzzards are very patient and it’s possible the bird was sitting on the post just waiting for the next thermal (rising bubble of warm air) to depart before it left. We have a home on a ridge in a forest clearing with rocky soil and enjoy the 7 vultures who live in the forest below us. Our rocky field is the gather place for both birds and humans of a similar persuasion (glider pilots). Both my wife and I are glider pilots and love watching how efficiently the critters utilize the available lift.

Reply to  ferdberple
May 23, 2017 7:06 am

What is entirely missing, from this discussion of warm air convection and cut grass, is that water vapor also lowers air density, water vapor being 37% less dense than air. The tall grass would have much more water transpiration than the cut, mostly dead grass that also shades the living portions. It is the humidity of the air that works with warming that causes the convection the birds are looking for.
Humid air can contain 10 000 to 30 000 ppm water vapor and greatly increases air buoyancy.

May 22, 2017 9:27 am

Once I watched a cat pounce on a peacock, which immediately flew off with the cat falling to the ground. Sort of like the Looney Tunes chicken hawk chick taking on the big rooster: “I’m a chicken hawk an’ I eats chickens.” –AGF

Reply to  agfosterjr
May 22, 2017 4:20 pm

As a kid, I once accidentally caught a big hawk in a gopher trap and it screwed up his leg. I saw it wasn’t broken so I threw the hawk in a big cage so his leg could heal. I fed it mice and small birds. But I was
afraid it wasn’t eating well enough so I threw a leghorn hen in to it. That hen beat the crap out of my poor hawk. I had to rescue it. Anyway, its leg healed up, and my dad got tired of hearing it screech and let it out. The hawk hung around for a couple of weeks looking for a handout, but he stayed perched on things at least a hundred feet away. Nobody fed him so he eventually left.

Myron Mesecke
May 22, 2017 9:39 am

Not really related to the topic but on my daily morning commute I pass an open lattice style cell tower in a small town (rural area) just off the edge of the interstate. Often see a dozen or more buzzards on it waiting for the air to warm. If you mention the buzzard tower to regular drivers they know what you are talking about.

Reply to  Myron Mesecke
May 22, 2017 11:12 am

I taught a flock of several hundred Blackbirds not to land and take up residence in the trees surrounding my house every spring. They learn pretty fast. They come around every year, but they now land in trees several hundred yards from my house. I sure am glad they are fast learners because they made one heck of a mess.
My method of teaching was to take a baseball bat and wait until they all landed in my trees and then I would beat on the side of a metal storage shed I had, and it sounded like gunshots, and the blackbirds would fly into the air and circle around and then come right back to where they were, and then I would make more noise, and after doing that for a few times each spring for a couple of years, they never land in my trees anymore, even though they come through here every year.
I have not had to beat that storage building for many years. 🙂

Reply to  TA
May 22, 2017 12:33 pm

Migratory birds follow their leaders. New leaders learn the time-tested routes from the old leaders.

Reply to  TA
May 22, 2017 4:29 pm

Blackbirds live a long time. Something like 40 years. It’s probably been 20 years since I trained the flock, so the flock might have the same leaders, or as chimp said, the new leaders learn from the old leaders.
Some blackbirds are supposed to be better at solving problems to get food, than are dogs. And I have read stories where they supposedly can recognize individual humans. I wonder if they recognize me when they come around. They probably say to themselves, “Hey, there’s that noisy fellow over there.”

Reply to  TA
May 22, 2017 5:13 pm

Crows can definitely recognize individual humans.
Twenty years would be a long time for a blackbird in the wild, especially if it were already the leader. But it’s surely possible for it to be the same bird.

May 22, 2017 9:45 am

“I couldn’t cut it earlier because of the endless rain”
Ever consider the effect of evaporation on temperature? You don’t get thermals over a cool surface, which is what you created by exposing damp ground.
Birds have bird brains, reptiles have reptile brains and God gave each of His creatures abilities far beyond our understanding.

Reply to  ian
May 22, 2017 9:55 am

Birds are phylogenetically reptiles. Their brains are thus reptilian, lacking the mammalian neocortex. Yet some of them can reason and make tools. The crow family are the smartest, then parrots. Their bird brains are marvels of miniaturization.
“God”, whatever you suppose that to be, has nothing to do with it. Please don’t bring religion to a science blog. Thanks.

Reply to  Gabro
May 22, 2017 11:33 am

““God”, whatever you suppose that to be, has nothing to do with it.”
And you know this because…
” Please don’t bring religion to a science blog. Thanks.”
He believes God exists & is relevant, you don’t. Sounds like you are equally religious, except he doesn’t tell you to shut up about yours.

Reply to  Gabro
May 22, 2017 11:47 am

Nope. No religion involved in concluding that birds have reptilian brains. It’s simply a scientific observation, ie a fact.
In science, you need evidence. There is no evidence whatsoever that “God” made the brains of different classes of animals, and all the evidence in the world against it, since a designing agency wouldn’t have made so many mistakes in sensory and input processing apparatus.
“God” is not a scientific hypothesis because it can’t make testable, falsifiable predictions. Such a thing might well exist, but there is no scientific evidence in support of this baseless conjecture. It’s solely a matter of blind faith, entirely evidence free.
That related animals have evolved similar brains is OTOH an easily tested hypothesis.

Reply to  Gabro
May 22, 2017 4:05 pm

“since a designing agency wouldn’t have made so many mistakes in sensory and input processing apparatus.”
Mistakes by whose standards? How many living organisms have you designed and built?
Be very careful when you accuse something of being a “flawed” design. Even with things designed by men. Very often that “flaw” is actually quite ingenious engineering. Other times it is because the designer had diffrent goals in mind than you do.
Remember how atheists used to use the Mamalian eye as an example of bad design? Oh how science progressed and bit them in the balls like a rabid wolverine over that.
What used to be considered bad design is now considered quite optimal design. The nerves need to be in front of the retina so that the retina can be right up against the rich supply of blood vessels that supply food and oxygen, as well as carry off the waste heat from retinal metabolisim.
The nerve cells in front of the retina quite slender and mostly clear, so they don’t block much light in the first place. Recent discoveries on the function of muller cells shows them to be living fiber-optics and not just support cells. They guide light around the nerve cells, focus it further, and diffuse the overabundance of blue light onto the rods of the eye. That’s just what we have learned so far.
We can go on and on. Apendix? Bomb shelter for good intestinal bacteria for when there is an infection. Tonsils? Part of the immune system.
Atheists throw their arms up and say “bad design” the same way people 3,000 years ago did and blamed sorcery when they saw things that they didn’t understand.

Reply to  Gabro
May 22, 2017 5:56 pm

Instances of intensely stupid “design” abound.
Please state what advantages you imagine that tarsiers, Old and New World monkeys and apes, to include humans, get from not being able to make our own vitamin C. Also guinea pigs, capybaras and most bats, whose vitamin C genes are broken in different places from the primate gene. Lemurs and lorises still are able to make their own vitamin C, like most mammals.
Then please explain why it’s intelligent design for our gonads to arise in our chests, as in fish, amphibians and reptiles, then migrate out of the body in male mammals, due to our high body temperature, when this sets us up for hernias?
Next, please tell us why the human foot is so subject to flatness. Only an idiotic designer would create such a jetty-built structure. Clearly, a foot adapted for grasping in trees had to be rerigged for walking plantigrade on the ground.
I could go on for dozens of examples of atrocious design, just off the top of my head.
There is zero evidence of “intelligent design” and overwhelming evidence of profound stupidity on the part of any alleged “designer”.

Reply to  Chimp
May 22, 2017 6:55 pm

Nah. If it works, then it is an intelligent design.

Reply to  Gabro
May 22, 2017 7:02 pm

Humans and our closest primate kin can’t make vitamin C, yet it works for us because we get it in our diet, until we don’t, in which case we die of scurvy. Why would an intelligent designer afflict such an odd assortment of mammals with the scourge of scurvy?
Does the supposed designer hate simian primates, South American cavy rodents and bats so much that we have to suffer this scourge, while, you name it, pigs, whales, naked mole rats, hippos, least weasels, whatever, are favored with abundant self-produced vitamin C?
And why do humans, other apes and monkeys still have the muscles to move our ears, when we can’t move them to help locate the sources of sound?
Why do flightless beetles which can’t even open the carapaces covering their wings still have wings?
As I said, I could go on and on and on with instances of intensely stupid design. As the devout Orthodox Christian Dobzhansky so rightly said, “Nothing in biology makes sense except in the light of evolution”. His specialty was the insects of Hawaii. I defy anyone to study them and try to maintain the lunatic delusion of “ID”.

I Came I Saw I Left
Reply to  Gabro
May 22, 2017 7:50 pm

” Why would an intelligent designer [whatever].”
Maybe to confound an arrogant, presumptuous person like yourself.

Steve T
Reply to  Gabro
May 23, 2017 2:18 am

May 22, 2017 at 5:56 pm
Instances of intensely stupid “design” abound.
Please state what advantages you imagine that tarsiers, Old and New World monkeys and apes, to include humans, get from not being able to make our own vitamin C. Also guinea pigs, capybaras and most bats, whose vitamin C genes are broken in different places from the primate gene. Lemurs and lorises still are able to make their own vitamin C, like most mammals.

I don’t want to get into the debate on intelligent design, but my understanding of evolution theory says that making one’s own vitamin C is a very high cost to the individual organism (relatively). Why bother if it can be obtained easily from the environment – of course there will always be individuals that don’t get it, but not enough to alter the survival equation. The animals whose usual diets do not include good sources of vitamin C have, on the whole, retained the ability to make their own vitamin C.

Reply to  Gabro
May 23, 2017 7:30 am

Sorry, don’t have link, but I read recently that the lack of human ability to create its own vitamin C was possibly due to the effects of a virus…

Reply to  Gabro
May 24, 2017 5:16 am

Existence exists. That which exists exists. It is what it is and is not what it is not.
Existence exists is the axiom of both Qaballah and Objectivism. Let he who has eyes see, he who has ears hear.

I Came I Saw I Left
Reply to  ian
May 22, 2017 12:27 pm

Evaporation is what I was thinking, too. Saturated ground cooled from the rain. Then lots of evaporation. Makes most sense.

I Came I Saw I Left
Reply to  I Came I Saw I Left
May 22, 2017 1:15 pm

That cut grass was loaded with moisture. A lot of heat went into turning it brown. Like a rice cooker. the same heat will cause the heating plate temp to rise once the water is gone, automatically cutting it off.

Reply to  Willis Eschenbach
May 22, 2017 1:49 pm

It might be useful to think of a grass plant as an evaporation machine. Cut back the machine and you cut back the amount of evaporation.

Bill Murphy
Reply to  Willis Eschenbach
May 22, 2017 3:29 pm

“lots of variables” is exactly right. Experienced sailplane pilots will tell you that even very reliable thermal spots will occasionally go “flat” for no obvious reason and no change on the ground. Probably due to changes in RH and barometer resulting in more stable air. It may be, Willis, that cutting the grass had no effect at all, you just timed the mowing with a few days of what sailplane pilots call a “flat day.” I remember one spot north of Phoenix where I used to fly that had a very reliable thermal that was nearly always good for 2000 feet or so of altitude. Then one (particularly flat) day I was “scratching out” looking for any lift at all and headed over there only to find not only no lift (and no buzzards or hawks circling like they normally did,) but a slow sink. The end result of that was similar to what your buzzard experienced: I made it back to the glider port with only a few feet to spare after psychically lifting my feet to clear the trees at the end.

Reply to  Willis Eschenbach
May 22, 2017 5:50 pm

I fly radio control sailplanes and used to fly on a sod farm that was often wet. One time half the field has been harvested, leaving rich brown (almost black) ground. We thought it would be a thermal machine, but while the ground was wet, you could tell you got over the harvested area because the airplane would suddenly start dropping. Once the ground dried out, it made good, consistent thermals. I had never thought humidity would affect performance that much. We also used to share our airspace with turkey buzzards. They would sometimes start circling until we went over to share their thermal, then flap of, leaving us in dead air. You could almost hear them snickering at the stupid, stiff winged birds.

Reply to  ian
May 22, 2017 5:23 pm

Gabro. Your position on bird evolution is a “just so” story. It is a religious position taken on blind faith. Your sources see one single similarity and create something out of whole cloth from it. There are vast differences between bird and reptilian brains.Even Archaeopteryx (now recognized as a true bird) had a uniquely birdy-brained feature called a wulst. The wulst is a cerebral indentation important for information processing and muscle control. Reptiles, living or extinct, do not have one. If you want to take a truly “scientific” position on bird brains, then you need more than a claim that you are right and everyone else is wrong. You need to carry out experiments that demonstrate your claims. Of course, you can’t do that. Neither can I do an experiment to demonstrate God to you. The overwhelming evidence that I could produce for God’s handiwork in Creation would not cause you to believe in God either. Evidence requires a framework of belief before you will accept it. If evidence exists that does not fit into your preconceived worldview, then you will just reject it. This is why you will never convince a “true believer” in Global Warming to change their position. Their position is a religious “worldview” that is not open to debate.
ian (yes, I have a degree in biology and a private pilot’s license …)

Reply to  ian
May 22, 2017 5:47 pm

As is typical of creationists, you could not possibly be more wrong.
The fact that birds are reptiles is based upon every possible parameter, not just one.
You really ought not to comment upon topics about which you are totally ignorant.
Birds are not just reptiles, but archosaurs. That means that they are more closely related to crocodilians than to lepidosaurs, ie squamates (snakes and lizards) and tuataras. That birds and crocs are archosaurs was long established, based upon shared derived anatomical traits, but in recent decades biochemistry and genomic comparisons have confirmed the relationship, which was obvious from both cranial and post-cranial structures.
The beta keratin of crocs is the same as that not only in birds, but in their closest extinct kin, other theropod dinosaurs.
Somehow you managed to study biology without learning the most elementary facts. A sad commentary on our educational systems.

May 22, 2017 9:45 am

I worried about the buzzards over our clearing, here in Gualala 50 miles north of your clearing. I thought it was personal.

Reply to  Willis Eschenbach
May 22, 2017 4:26 pm

Round about where I live, about 7 minutes from downtown Oakland, they conserve energy to hop on the roadkill when it’s clear to go. Thanks for the post Willis:
…. and by the way, real buzzards are much prettier than turkey vultures.

May 22, 2017 9:45 am

The cut grass is a flat plate 2D heat absorber. The growing grass is 3D so has more surface area. The growing grass also has more mass to absorb and hold heat due to the moisture it contains. Also it’s color is darker.

Reply to  Greg
May 22, 2017 11:22 am

We call them turkey buzzards. I live on the west side of a lake. The buzzards like to visit when the breeze is from the east. The uprising land, trees and houses create updrafts. It’s annoying because I have an idiot english springer that feels it’s his duty to race around the house barking at the birds. I guess to the dog’s POV his barking has 100% of the time (so far) driven off the invaders…. eventually.

Reply to  taz1999
May 22, 2017 11:29 am

btw the buzzards are sometimes nuisance on the towers and some glassed buildings (also updrafts) Turns out you can shoo them off by hanging a dead one out.

Reply to  taz1999
May 22, 2017 11:55 am

OOOOH! Dear Taz per your note below about hanging out a dead buzzard. If you live in the USofA you could get into serious trouble if you helped to make that buzzard dead and even if you didn’t kill it simple possession is problematic.

Reply to  taz1999
May 22, 2017 12:00 pm

JustAnOldGuy. Interesting that you point out the legality. Where I saw this in practice was a city run communications tower. I guess the sovereign is immune.

Rhoda R
Reply to  taz1999
May 22, 2017 12:22 pm

They aren’t called ‘bird dogs’ for nothing. I had a Cocker Spaniel that was the same way about ANY bird in the yard. Also leaves in the fall. If it was in the air he’d go nuts after it.

May 22, 2017 9:52 am

” my mamma done told me, bring home something for dinner.”

Reply to  Scott Frasier
May 22, 2017 2:14 pm

Great Bugs Bunny !

May 22, 2017 9:53 am

There is no CO2 in this story. Would it make a difference if the grass had another colour? What happens when there is snow on the ground?

Reply to  Robertvd
May 22, 2017 9:56 am

the grass had gotten up to about chest high…CO2

Reply to  Latitude
May 22, 2017 4:30 pm

…. not to mention the IPCC’s 3 degrees of warming from the half-doubling of CO2.

Reply to  Robertvd
May 22, 2017 10:08 am

Temperature in the clearing must be lower when the grass isn’t mowed because the rising air is replaced by cooler air from the forest.

Reply to  Robertvd
May 23, 2017 6:55 am

The buzzards would go south.

May 22, 2017 9:54 am

A most interesting post as always, Willis.
Maybe there’s a glider pilot on here who could relate his/her experiences in thermal-hunting over varied terrain? My brother, who was a mad keen aero-modeller back in the 1940s, sometimes lost one of his rubber-powered aircraft to thermal activity. They flew for miles.

Reply to  Luc Ozade (@Luc_Ozade)
May 22, 2017 10:11 am

Here’s a discussion of thermals, including terrain effects:

Geologist Down The Pub
Reply to  Luc Ozade (@Luc_Ozade)
May 22, 2017 3:21 pm

I’m a (retired) competition sailplane pilot, and have always wondered why some green surface areas were better thermal generators than others. Asphalt parking lots and quarries of dark rock are obvious and easy. But we sailplane drivers rely on the same thing the vultures do – instrumentation. We have a thingy in the cockpit called a variometer, while the vultures (and other soaring birds) have an analogous organ in their heads. These devices sense whether the aircraft, feathered or carbon fibre, is in rising or sinking air, so the pilot banks one way or another to compensate. Frankly, the vultures are smarter at this then I ever was.
Yes,l it is possible to fly for miles in thermals, if you can find them and stay in them. The average saliplane race is over 200 miles om the NE USA.

Nick Stokes
May 22, 2017 9:55 am

What grass is good for is boosting evapotranspiration. All those xylem tubes. And water vapor is a lot lighter than air

Ron Williams
Reply to  Nick Stokes
May 23, 2017 1:36 am

Well then, you would be talking about a water pipe…

May 22, 2017 9:57 am

People take hours of lessons before they fly. A bird’s single lesson is the time between the nest and the ground.

Reply to  rovingbroker
May 22, 2017 12:56 pm

Nice quip, but not exactly true. The parents like to move the young out as soon as they can flutter some. The nest is a fixed point that a predatory cat or other critter can locate and lurk around. That puts both the parents and the young at risk. So they urge the young to mobility before they can fly efficiently. Quite a lot of the young birds that are “rescued” by well meaning folk are perfectly fine and making the transfer from – roughly – childhood to juvenile states.
Essentially they go through the same developmental stages we do. Infancy (more or less immobile), toddler (a little staggery but no possibility of flight better than a brick), childhood (fluttering to more sophisticated gliding), and finally juvenile with their pilot’s license. Once they can flutter successfully from bush to bush, the parents urge them away from dangerous places like nests and keep them moving, which strengthens them and exercises their wings and reflexes.

Reply to  Duster
May 22, 2017 1:07 pm

Heh. Last Friday I had to keep taking a teen age bird back outside when it persisted in hopping in the open door of our factory. I didn’t just put him out the door, but across the yard among a nice pile of metal racks. Yet a half hour or so later, there he was back. Maybe the dim factory seemed like a good sanctuary similar to what you’d find under a tree?

D. J. Hawkins
Reply to  Duster
May 22, 2017 1:21 pm

This has been my observation as well. When I was 9 or 10, I’d see the fledglings hopping around on the ground and try to “rescue” them. Unless you could get one into a corner, they were almost always able to hop/flap/glide from bush to ground and back just out of reach. I’m sure I too had thought that if the youngster couldn’t take full flight out of the nest he must need help.

Reply to  Duster
May 22, 2017 3:51 pm

I tried to ‘help’ (actually keep) a feral kitten once. The whole litter had been taken by a neighbor to keep (feral cats are great mousers) and they were struggling to get back. They wer all extremely young, and could not even walk terribly well.
I still have the scars today, 30 years later. Can’t walk, but can bleeping well defend itself!

May 22, 2017 10:00 am

Great story, Willis. That this stage “A field of overgrown, well watered grass give more thermals than a mowed field” is a hypothesis looulking for confirmation. The explanation make sense.
But if it were true, why does not the forest around the clearing, even darker and thus with a lower albedo than either the mowed or unmowed field give off even more thermals. Do not the buzzards ultimately\\ depend upon the difference in air rising and falling over different terrains? Is what you observed partially dependent upon what is around the mowed field?
BTW, was the picture of the buzzard on the post from that instant in the story?

Reply to  Stephen Rasey
May 22, 2017 12:16 pm

The turkey vulture on the post is soaking up photons to boost its low metabolism. They release fat slowly, due to often long periods between meals, so aren’t as warm blooded as most birds.
In July 1863, turkey vultures and their smaller, black-headed kin flocked to Gettysburg by the thousands to feast on dead horses killed in the three-day battle. Many stayed and their descendants are still there.

May 22, 2017 10:06 am

How many square miles of wheat, rye and other tall narrow plants are there (and their change over time)? How many temperature equivalent measuring stations do they represent in at least the United States? Is this agriculturally mediated temperature increase raising rural temperatures?
Do the IPCC/NOAA models account for this?

May 22, 2017 10:08 am

Cut green grass dries in the sun. So the sun’s energy is going into water vapor formation with its latent heat of evaporation more than into a rising thermal air convection cell. So less buzzard lift because of evaporative cooling until the hay is dry enough to be baled. Freshly cut and drying alfalfa contours at the farm are discernibly cooler on a windless day than adjacent contours of growing corn or soy.

May 22, 2017 10:08 am

Looking at the picture of the cut/uncut grass, I come to this conclusion:
The cut dried grass is considerably more reflective so heat is reflected away rather than being absorbed and thus cannot warm the air.
If you raked the dried grass off the field, it would again absorb heat and heat the air.

Bruce Friesen
May 22, 2017 10:09 am

Wonderful reflections on the natural world, as always, Willis.
A glider pilot would think about moisture.
Yes, the sun heats the ground. Energy transfers from the ground – leaves, dirt – to air molecules that contact those surfaces. The air becomes more energetic (“warmer”), expands, becomes less dense hence buoyant. Given a bit of a kick, it will start to rise.
However, in parallel, the sun heats the ground, water molecules in the ground – in and on leaves, in the soil – become more energetic, evaporate to the vapour phase, and join the air. Because water molecules are lighter than oxygen molecules and nitrogen molecules, the higher vapour content makes the air less dense hence buoyant. And off we go!
Glider pilots have convinced themselves the latter process dominates.
If that is true, the question we are trying to answer is “why did the tall grass contribute more water vapour to the air that did the cut grass?” If I was less lazy, I would speculate on the answer to that question.

Reply to  Bruce Friesen
May 22, 2017 10:45 am

It seems extremely unlikely that grass, whether cut or uncut would lose more water through evapotranspiration than the surrounding redwood forest. Particularly as redwoods are C3 plants and most grasses C4.

Bruce Friesen
Reply to  tty
May 22, 2017 11:13 am

It’s a quandary, isn’t.
I believe the answer is inertia. A blob of less dense air – less dense because it is warmer or less dense because it is moister – will just sit there until something gives it momentum. Glider pilots expect thermals in locations where a blob of lighter air gains some vertical momentum, such as the treeline at the downwind edge of a field, a tractor working a field stirring things up, and so forth. Without something kicking things up, nothing moves. Consider the tonnes of atmosphere resting on that blob of light air, holding it down. It needs a push, a little start, to muscle its way upwards. Once it starts moving, up it goes, dragging its buddies along with it (including air from within surrounding groves of trees).
So why not the redwood forest? I believe the answer is the word ‘relative’: that it is relatively easier for the wind or the tractor to start the air above a bare field moving than to start the air within the forest canopy moving. Indeed, glider pilots hope for thermals over forest later in the day, after the sun has done its work, and the lighter air over fields has all risen, yet there may still be masses of light air contained within the forest canopy. Relatively less likely to gain momentum, but definitely unstable.

Gary Pearse
Reply to  Bruce Friesen
May 22, 2017 2:48 pm

Light high water vapor-air mix rises, but it wouldn’t have the lift of dry air rising at the same rate. Like a boat in water, it would be more buoyant than say alcohol, or if a sudden rise of methane bubbles (Bermuda Triangle anyone).

Robert of Texas
May 22, 2017 10:19 am

The albedo looks different – when the grass dries it appears to become a better reflector and is sitting on top. Could be reflecting more potential heat energy away.
You also shut down a lot of water transport and evaporation as some have mentioned.
You also reduce air movement “friction” close to the ground, so that air can more effectively mix.
Have you tried using a simple infrared thermometer like one uses in a house to find air leaks? If you are correct, the surface of the cut grass should be cooler than the surface of the uncut grass.
But just as likely, its just different conditions on the day you made your observation. The wind flow, direction,humidity, temperature, etc. could all play a factor. So until you understand the Natural system, you can’t really say much about man’s changes to it. Hmm, sounds like a lesson in there somewhere for climate scientists.

May 22, 2017 10:31 am

Flying from Denver to Aspen on a really hot day can be a harrowing experience because air lift depends on the altitude of the mountains and valleys below.

Reply to  Mohatdebos
May 22, 2017 10:47 am

Flying low over a desert in daytime is even worse because of the intense small scale convection.

Gary Pearse
Reply to  Mohatdebos
May 22, 2017 3:10 pm

On a mining exploration trip in 1970, myself and assistant were taken up to near the top of Seven Sisters mountain near Prince Ruppert, B. C. in a jet Ranger helicopter. Several days later when he picked us up it was with a Bell G2(?). We got in with our gear and the craft skittered and hopped so he got one of us to get out while he flew to the edge of the cliff above a glacier. He lifted off and we free fell several hundred feet. When I saw the white knuckles and stony look of the pilot, I realized that I should be a heck of a lot more scared than I had been. Fortunately we began to get forward motion and we wound up dodging tree tops still descending over the stream falling away from the glacier before we got lift. The pilot admitted he shouldn’t have been flying the small craft for this job. Probably no trouble if the wind was blowing toward us.

Reply to  Mohatdebos
May 22, 2017 3:34 pm

Pretty harrowing in winter too. Aspen Scareways.

May 22, 2017 10:33 am

Need to keep in mind also that moist air is less dense than dry air.

May 22, 2017 10:39 am

That grassy areas in forests are good for thermals has been known to glider pilots for a long time.
That fact even played an important role in one of the early engagements of the Pacific war, the Lae-Salamaua raid in March 1942 when aircraft from Lexington and Yorktown staged a surprise raid on Japanese amphibious forces landing at these two ports. The raid really was surprise since the carriers had approached undetected “below” New Guinea and attacked from over the then virtually unexplored Owen Stanley mountains.
The Owen Stanleys are high and very rugged and infamous for bad weather and turbulence even today.
The striking force consisted of a mixture of F4F fighters SBD dive-bombers and TBD torpedo bombers. The F4F and SBD were good enough aircraft for 1942, but the TBD “Devastator” was quite frankly an obsolete clunker, vastly inferior to its’ Japanese counterpart B5N “Kate”. Among (many) other faults the TBD had a derisory climb-rate and service ceiling, particularly when carrying a torpedo, and it was dubious if they would be able to get across the mountains in a loaded condition.
As the torpedo squadron was getting close to the pass it was clear that they wouldn’t make it, but fortunately the squadron commander was a sailplane pilot and he spotted a grassy knoll in the otherwise unbroken rainforest. He flew over it and, as he had hoped. there was a thermal there that gave them a few fps extra climb rate, just enough to clear the summit.

Reply to  tty
May 22, 2017 11:06 am

The USN had a lot of luck in the Pacific in 1942, but the TBDs didn’t share in it. They were practically wiped out at Midway. Carriers Lexington and Yorktown were also sunk, at the battles of the Coral Sea (May) and Midway (June), respectively. Hornet then was lost in October, leaving just Enterprise.
It is suspected that FDR was warned about Pearl Harbor, hence the carriers were all at sea on Dec. 7, 1941.

Tom in Florida
Reply to  Chimp
May 22, 2017 12:12 pm

Nothing from Washington. Here’s a good read on the inquiry that followed;

Reply to  Chimp
May 22, 2017 12:27 pm

A lot has been revealed since 1944. Naturally, the administration wanted to cover up.
Washington knew from a number of different sources that the IJN fleet had steamed from the Kuriles, headed east, not south. The carriers didn’t maintain strict radio silence. It’s known that their transmissions were picked up in the Philippines and Hawaii, but a highly respected man in my hometown, a USN radioman in 1941, also heard them at Mare Island Naval Shipyard, in SF Bay.
There were lots of other warnings. FDR wanted to get in the war, had tried everything he could o sucker Germany and Japan into declaring war or attacking, so was willing to let thousands of sailors, soldiers, airmen, Marines and civilians die to achieve his megalomaniacal goal of world domination.

Reply to  Chimp
May 22, 2017 12:59 pm

Too bad the U.S. Battleships were not out in the open sea with the carriers. They didn’t have much of a chance tied up to the dock. If you have to go, at least you ought to get the chance to go down swinging.
The Japanese planned the attack well. I guess they thought the attack would break the spirit of Americans. Instead, it did just the opposite. Admiral Yamamoto told them, but they wouldn’t listen.

Reply to  Chimp
May 22, 2017 1:17 pm

The BBs sunk were old, and most damaged ships were recovered. The obvious exception is Arizona.
The IJN wouldn’t have attacked had the whole Pacific Fleet been at sea. They had spies in Pearl.
Yamamoto hoped to get the carriers. Had he done so, the US would have concentrated even more on Europe until we could build new ones. H!tler obligingly declared war on America because he wanted to give his subs free rein to attack USN convoy escorts (“armed neutrality”). He miscalculated, thinking that we couldn’t fight a two-front war.

Reply to  Chimp
May 23, 2017 10:27 am

“Too bad the U.S. Battleships were not out in the open sea with the carriers.”
Actually it was probably lucky they weren’t. If they had, Admiral Kimmel would probably have stormed into the Mandatet Islands with them and been slaughtered by japanese torpedoes like Prince of Wales and Repulse

Reply to  Chimp
May 23, 2017 10:42 am

Japanese Long Lance torpedoes worked, unlike American ones until late in the war. Had they worked in 1941-42, USN subs could have sunk the Japanese troop ships invading the Philippines.

Reply to  Chimp
May 23, 2017 11:12 am

These were, unfortunately, “perfectly” designed “state-of-the-art theoretically-best-in-the-world fuses and torpedoes.
Unfortunately, they were never properly tested under real world conditions. (Funney how history repeats itself, isn’t it? Har. Har. /thousands of unneeded deaths in WWII.)
The torpedo fuses were tested before the war.
But. The Navy “experts” wanted to save and re-use the (expensive) test torpedos after each shot. So they set the torpedoes to run too deep for the targets, deliberately wanting them to go under each target ship. Then, as we do now, they fired from a static “perfectly set up shot” so the magnetic fuse would be “perfectly tested” by the torpedo going exactly perpendicular to the target, right at midships. Well, ends up, the depth-controllers setting the wartime torpedoes were operating too low themselves. For example, instead of controlling the running depth at 6 feet deep that was dialed in, the torpedo was actually running 12-15 feet deep. The submarines would fire against a Japanese warship or cargo ship, the depth controlled setting was too low, and the torpedo would go underneath the target and not blow up.
Now, the Navy’s super-secret magnetic fuze was SUPPOSED to go off as it went underneath the target ship – so that near-miss-by-running-too-deep should not have been much of a problem , but the actual fabricated fuses did not go off from the ship’s magnetic fields. Or, more often, they went off early by being tripped by being too sensitive to the surface of the water and varying magnetic fields as the torpedo passed under waves. (True, that should not have happened, but it did. Worse, the “test torpedoes” deliberately set too deep to avoid blowing up the test torpedoes, could NOT show the magnetic fuses were faulty (too sensitive) because they were running too deep to be tripped by waves. And, the test conditions in shallow water in good weather and low winds, were never run in real-world waves and wind speeds because this was, after all, a “test” – not real battle conditions.)
SO, the early submarine skippers (those that survived the first few engagements, at least) turned off their magnetic fuzes (disobeying their admirals’ orders to do so!) to avoid early detonations. Well, then the too-deep-running torpedoes didn’t explode either because the nose impact fuse failed to hit the ship at all!
Well, the running-too-deep problem was eventually fixed. (After many sub skippers were blamed for bad shots by the Navy bureacrats in the torpedo labs. (Seem familiar?)
But the impact fuses had a second failure built in. If the torpedo hit perfectly dead-on (an exact hit on a perpendicular steel ship hull), then the detonator ram (a thin metal rod sticking out of the front of the torpedo) collapsed and jammed. It did NOT go back to hit the detonator train but bent and twisted in the fuze guide rods. (Again, a good aim, a good shot, but no explosion!) Paradoxically, if the torpedo was impacting at a slight angle (a poor shot, instead of a perfect shot), then the detonator rod would work. So there WAS evidence that the designs and the models “worked” as designed!
It took some very, very determined sub commanders some dedicated and dangerous “testing” against actual enemy ships to get enough evidence to finally fix all of the problems. And the Navy government labs did almost NOTHING to find or correct the problem. They sat back and blamed the skippers shooting. Because, theoretically, their designs and “models” of how the designs were intended to work worked perfectly.

May 22, 2017 10:55 am

The New World “vultures” (which they technically aren’t) have been placed in their own order, Cathartiformes. It includes the two condor genera, each with just one species.
The largest or second largest known flying bird, Argentavis magnificens, a member of the teratorn family from the latest Miocene Epoch (~6 Ma), has tentatively been assigned to this order.

May 22, 2017 10:57 am

Willis, perhaps the Buzzard just saw you as breakfast and was coming in to see if breakfast was ready yet 😉

May 22, 2017 11:10 am

An astute observation and a credible analysis, sir! I would love to see t he results of a controlled test of this hypothesis – perhaps with adjacent fields mowed and unmowed in an area frequented by soaring birds for its updrafts.

Pop Piasa
May 22, 2017 11:17 am

Willis, you are the Norman Rockwell of storytellers. Always portraying the story with eloquence and charm.
Your works are appreciated.

May 22, 2017 11:43 am

I are’s a glider pilot and we go by color and time of day and topography and clouds, etc. Mostly though it is wind direction and velocity.
Moist air is less dense than dry air, especially moist warm air and it doesn’t provide much lift. Yeah it might be rising, but on a whole it may not do much. We aren’t talking about afternoon thermals ( I don’t think) which are a different animal and very powerful.
What we really look for is albedo changes and try to pick the lift side and avoid the downward side. Another thing that makes it hard is that it changes during the day a hillside in the morning that reliably produces lift often reverses in the evening after the surrounding area has warmed up.
I am guessing that cutting the grass field lessoned the albedo difference between it and the surrounding area, taking away all of the lift.

May 22, 2017 12:17 pm

A Turkey Vulture’s main defensive ploy when cornered is to project vomit profusely on the attacker. A friend who worked around them while studying wildlife management in college said a mere whiff of their vomit produces instantaneous violent retching in humans. Also, the ground under their favorite roost trees stinks to high heaven, quickly becomes barren, and the roost trees themselves may well eventually die. The birds sometimes circle in numbers over natural gas pipeline leaks, since a key ingredient in the odor of carrion is ethyl mercaptan, the same substance added to odorless natural gas so that humans can readily smell it.

Reply to  brians356
May 23, 2017 10:29 am

New World vultures are virtually unique among birds by having a keen sense of smell.

Reply to  tty
May 23, 2017 10:39 am

From 1988, when Paul Ehrlich still participated in science:

May 22, 2017 12:32 pm

I may make a couple of comments on this. But first and foremost, check the barometric pressure and temp at the time . Was it rising, steady, or falling? Key parameters.

May 22, 2017 1:39 pm

Thermals are more indicative of warm “ground” and less warm ground. The notion that the ground may feel cooler having given off its heat is hard to accept. Not saying it isn’t so, just hard for me to understand. Because I see an asphalt parking lot being a generator of thermals.
I suppose it doesn’t take much temp differential to fire off a thermal. A thermal can pop from different parts of a uniform field over the course of time.

Rob Dawg
May 22, 2017 1:42 pm

From where I post I can literally look up and see the Sespe Condor Sanctuary to the north. California Condors surviving because of a fortunate name. Had they been named Fillmore Ugly Dumb Scavenger Vultures no one would be missing them. In tough times they would travel here and nibble on the inevitable roadkill. The recent rain has meant they are not as desperate and sticking closer to home.

Reply to  Rob Dawg
May 22, 2017 1:59 pm

IMO they’re big enough, with eight to ten-foot wingspans, to have attracted attention even were they not named condors.
I’ve been buzzed by Andean condors in the mountains above Santiago, Chile, not because I smell like rotting flesh, but because the scavenger was swooping in on a dead cow.
The two species overlap in wingspan, with Andeans typically bigger and heavier birds. California condors ranged much more widely in North America during the Pleistocene, when there were so many megafauna to scavenge.

Reply to  Chimp
May 22, 2017 2:57 pm

Minnesota Fats once said: “They say there’s only eighteen California Condors left in the wild. If one craps on my Cadillac, there’ll be seventeen.”

Reply to  Chimp
May 22, 2017 6:31 pm

I once shot and ate a condor. The meat taste something between a baby seal and an eagle!

Reply to  Chimp
May 22, 2017 6:47 pm

Eagles aren’t endangered, so you get no un-PC style points for that. Neither are baby seals.

Reply to  Chimp
May 22, 2017 6:49 pm

Polar bears?

Reply to  Chimp
May 22, 2017 6:55 pm

Also not endangered.
Polar bears taste like seals.

Reply to  Chimp
May 22, 2017 7:04 pm

Hell, I’m going to get a big mack and a frosty. It’s not endangered but may make me sick!

Reply to  Chimp
May 22, 2017 7:24 pm

Is that a Big Mac made with polar bear meat and a Frosty with baby seal blubber?
I should hope so.

James at 48
Reply to  Rob Dawg
May 23, 2017 1:37 pm

The Fillmore part would have been the single word that did ’em in. 🙂
(Sorry, couldn’t resist, I used to live somewhat near there .,… ).

May 22, 2017 1:52 pm

My theory:
1. Albedo. Less Sunlight is reflected, all heat goes into the tall grass. Maximum heat input.
2. At an eara with cut grass the heat goes into the soil, wich is heated up. Ist is only released later or at night. No lift for the buzzards.
3. Long grass is a good heat exchanger through higher area. All available in the grass goes into the air – maximum and immediate heat release of all availabe energy.
Any sunlight wihich comes in is immediately used to heat the highest possible amount of air and give maximum lift.

May 22, 2017 2:01 pm

I see other people already thought about transpiration, and since moist air rises, the long grass likely would contribute to lift the vultures love so dearly. They certainly couldn’t care less how the lift is generated, so long as they don’t have to flap.

Don K
May 22, 2017 2:24 pm

Might be of interest to measure the air temp a couple of meters above the cut area and the uncut area. Hopefully it’ll confirm that the air above the uncut area is warmer. If it doesn’t … I dunno another hypothesis … vultures cause thermals maybe? Or we can just ignore the data and go with the model.

May 22, 2017 2:31 pm

is it possible there is also a relative humidity issue at play with the uncut grass vs cut grrass that causes more “uplift”?
very interesting observations, thanks for posting this..

May 22, 2017 2:40 pm

I do not think that humidity helps lift. Evaporation means cooling.
Just humid grass absorbs sunlight and gives immediately the minimum warmth to the air by contact, without much evaporation.

David Joyce
May 22, 2017 2:47 pm

Wonderful observations. I am a sailplane pilot and am always amazed at vultures ability to detect and use the smallest of thermals. Your observations show that they also base their abilities on local knowledge. Interesting hypothesis about the mechanism, wonder if evapotranspiration is playing a part.

May 22, 2017 2:59 pm

You know, it’s just possible those vultures simply partied too hard the night before. Think outside the box, folks.

Reply to  brians356
May 22, 2017 3:13 pm

turkey vultures drunk too much wild turkey perhaps?

Reply to  brians356
May 22, 2017 3:16 pm

Or one of their prey carcasses had fermented.

Brian Adams
Reply to  Chimp
May 22, 2017 11:26 pm

I’ve seen robins drunk on fermented berries. It’s comical, but they do become more vulnerable to predators like house cats.

Reply to  Chimp
May 23, 2017 10:33 am

Waxwings fairly often get drunk on fermented berries. They tend to fly into things, and to start singing for absolutely no reason in the middle of winter.
Not very different from humans actually.

Reply to  Chimp
May 23, 2017 10:44 am

I’ve seen intentionally drunk parrots staggering down a street in Panama City, apparently unable to fly.
Too drunk to fly, thanks to fermented fruit.

May 22, 2017 4:00 pm

Watched a flock of about 12 soar around my house a few minutes ago.

H. D. Hoese
May 22, 2017 4:08 pm

These must migrate, although have not seen that verified. We just had a bunch of black ones come in. There is a two mile causeway across the bay that pelicans and gulls, no vultures recalled, cross by riding the updrafts and there was a paper written about this long ago. Should have paid better attention, but wonder if thermals develop more in low winds off the Gulf when land heats up and cloud lines develop. During migrations they should benefit more with higher winds which they might get at altitude. One would think that someone has studied this, but probably not something that would get you tenure.

Brian Adams
Reply to  H. D. Hoese
May 22, 2017 11:36 pm

Turkey Vultures in N. America migrate south in winter. They return to where I live usually the same week every April.
Remember this classic poster? The warmista “climate scientists” are like these vultures: “Patience my _ss! I’m gonna predict something!”comment image

Reply to  H. D. Hoese
May 23, 2017 12:45 pm

Gulls seem to have the expert knowledge of all sorts of updraft: thermal, ridge lift, or any other disturbance that can give them a free ride. I was amazed to see them catch wake vortices from ferry boats I rode from Oyster Point to Oakland. It was not unlike a human surfer catching a wave with his board, except I had to use my imagination to visualize the wave they were riding. They used a special maneuver to approach and catch the vortex, and it only worked some of the time, but when it did work, it worked extremely well. They would hang in it for minutes, without flapping their wings (but with a fierce action on the stick and pedals, as it were), and once in a while one of them would dive and catch something. I noticed that they could tell from a great distance whether the ferry was of the right kind and did not bother trying if it was not; they also knew when wind direction or strength would affect vortex stability. There were two or three different types of ferry sailing on that line, and apparently one of them was not suitable for that sort of fun and they only flew by to check if it turned anything up in the water but never attempted to ride in its wake.

May 22, 2017 5:57 pm

A few have mentioned that a breeze always takes away the heat from the cut grass, but the tall grass is such a resistance that it turns any breeze to 0 mph, so all the sun’s heat stays in the tall grass and “cooks” it. This is what I believe is at work the most.
When I walk along the Lake Michigan shore on an onshore windy day, I’m always amazed that if I walk just inside the shoreline scrub brush treeline, the wind speed will drop from a nasty 25 mph to almost zero. Vegetation is very effective at nullifying a breeze.
[In the first 1/2 for grasses, first meter for shrubs, perhaps 1-1/2 meter for full bushes. .mod]

May 22, 2017 8:04 pm

Willis wrote

I expected that cutting the grass would increase the surface warmth and thus the lift for the buzzards. However, the buzzards proved me 100% wrong.

Of course it could have been as simple as you mowed in better weather typically associated with high pressure systems and general downward motion of the air whereas low pressure systems are associated with rising air moving the water to the sky where the clouds then form and it rains. And the buzzards get their lift.
The real test would be whether the lift returns over the next week or two despite the length of the grass.

Reply to  TimTheToolMan
May 24, 2017 6:07 am

Recalled local extension guy mentioning comparison of temperatures with bare soil, grass, trees just a few days ago, and tried to look it up. Of course, did not find it, but these few filtered from the false positives are interesting.
Had more elaborate notes, but the interface ate them.

Old Woman of the North
May 22, 2017 8:51 pm

Great observation, Willis.
A hang-glider told me he finds thermals by looking for little puffy clouds forming. They are where the moisture in the r condenses.
When we first got TV back in the 1970s on our farm the cattle dogs (outside dogs) were so fascinated they came inside and looked behind the set to find what was moving!

Anders Valland
May 23, 2017 12:03 am

I haven’t read all the comments, so maybe it has already been covered. I am a glider pilot, albeit not an experienced one, and we learn to distinguish between surfaces on the ground to look for thermal sources and sinks.
In your story you say that cutting the grass has been delayed due to a long period of rain. I would then assume that the ground was wet, and if so the ground would be sucking up a lot of heat because of this. It would therefore be less of a thermal source until dry.
The whole point here is that the buzzards fly on the temperature differential between the warm (and in this case moist) air and the surroundig air. If some other area is generating warmer air, then your field is the sink. After all, if some air goes up, other air needs to come down. A thermal is always covered in sinking air.
I think your initial hunch was good, but this example shows it is not always so.

Peta from Cumbria, now Newark
May 23, 2017 1:04 am

To my mind explains a lot of things, not least a thought I’ve had for some while.
The GHE says the atmosphere, very close to the dirt and esp. where people and thermometers are, is warmer than it should be (because of of Stefan Boltzmann’s Law) exactly because of the GreenHouse Effect.
Vertical things on the surface, grass, fairly isolated trees and of course buildings, will absorb more solar energy during morning & late afternoons than a flat surface.
The tall things will absorb along the lines of a cosine (of the sun’s angle above the horizon) curve while level surfaces will absorb along a sine curve throughout the day. But at noon time, even the vertical things look like a flat surface so the 2 curves must be added and that gives greater energy overall daily energy absorption.
The tall things also are typically not well connected thermally to the dirt, so they will achieve higher temperatures and dissipate this energy into the air near the surface.
At my old farm was a cement rendered breeze-block wall that directly faced the setting sun. Even on otherwise cool but clear days, the late afternoon heat coming off that wall was incredible. You could feel it from 3 or 4 metres away. And it was a very light grey colour, probably very high albedo.
Looking at real things in the real world explains why the GHGE is garbage, why the Urban Heat Island is a reality and why my old Cumbrian home farm was cooling.
Farming areas, especially livestock in the UK, are getting ever more intensive, the grass is being cut & grazed ever more often. Hence Willis’ observation.
In arable areas, the converse applies and they are warming – lots of low albedo dirt lying around and tall dark coloured plants (because of all the Nitrogen fert they get) that are good a collecting heat from morn till dusk yet efficient at dissipating it into the air.

May 23, 2017 1:13 am

“And in that vein, after avoiding the clearing for a couple of days, today for the first time I saw a buzzard come through. However, it didn’t push its luck, and it didn’t get close to the ground. The buzzard just came in, got the main lift from the center of the clearing, and wheeled back out again.”
Good observations as always Willis.
I think that tall grass acts like an insulator, protecting the soil from excessive drying. Think straw bale houses, thatched roofs etc
Cut grass exposes the soil surface to the harsh drying sun. It would take time, a couple of days in your case, for the sun to burn off the soil moisture.
During those couple of days, we have the cooling effect of the upper surface soil moisture being evaporated.
Once the upper soil has dried, thermals return, along with the birds.
I haven’t looked it up but I have a sneaky feeling that H2O and its phase changes has a stronger effect than albedo/colour/surface quality.

May 23, 2017 2:02 am

It would be interesting to erect a met tower and actually measure temperature and humidity at various heights above the ground and the fluxes.
Glad to see you are still around, Bruce Friesen.

Poor Richard
May 23, 2017 3:54 am

Wonderful post!
I might be wrong, but IMHO, it seems obvious that a field with tall grass would be a better heat exchanger than a field with short grass. More surface area.

May 23, 2017 4:39 am

Glider pilots tell me they will often share a thermal with birds of prey… and that inevitably they find the birds know where the greatest rate of lift is and position themselves there. A glider pilot has an instrument to measure the lift – they wonder how the birds are finding that sweet spot without one…

The Original Mike M
May 23, 2017 5:27 am

They have a very keen sense of smell to detect rotting flesh. Is it possible that convection has nothing to do with their change in behavior and it was really that cutting the grass killed some small varmints, (small snakes, field mice, etc.) so they came down to investigate the menu?
I propose a test Willis. Collect an adequate supply of fresh small critter road kill in the freezer, and when the grass is nice and high again – scatter it around on the morning of what will be a nice hot day and see if they exhibit this same behavior as when the grass was just cut.

May 23, 2017 6:25 am

Check your barometer. Even hot flue gases can’t rise when pressure is low or perhaps falling. Just take a glance at the smoke from local chimney in the area you hunt and if the smoke is not rising or if it’s falling even the best tracking dogs can’t work.
You will also not see any birds soaring. Ambient temperature also has an effect.

The Original Mike M
Reply to  eyesonu
May 23, 2017 8:28 am

“hot flue gases can’t rise when pressure is low”
Huh? They seem to rise just fine at ~15,000 feet, (~24.9″ Hg)comment image

The Original Mike M
Reply to  The Original Mike M
May 23, 2017 8:30 am

Ooops! 5000′ not 15000′ altitude, 28.3″ Hg

Reply to  The Original Mike M
May 23, 2017 8:34 am

I think you are conflating the very low outside air actual pressure (at low humidity and very high altitudes and very cold air temperatures – that DOES draw very strongly when passing heated firestove air!) with the low draws of humid (high relative humidity and low pressure regional air around the house) trying to “pull” air up an open chimney at 100 – 1000 feet altitudes.

The Original Mike M
Reply to  The Original Mike M
May 23, 2017 9:38 am

I should have picked hot air balloons as an example; they still go up when the barometer is low, (just not as fast). I don’t question the validity of the observation but suspect if there might be more going on to explain why smoke tends to hang lower in the air. I wonder if humidity could have an influence on the chemistry of the smoke itself to make it a little heavier?

Reply to  The Original Mike M
May 23, 2017 1:29 pm

My observations are generally between 1000 to 2500 ft above sea level. You can hardly get charcoal lighted in a starter chimney on a low pressure day.
Poured 5 gal old gasoline on a brushpile and tried to light it once on a low pressure system before approaching rain by throwing burning newspaper ‘comets’ (rocks wadded to allow throwing) on the wet fuel. I ran out of paper and matches. No fire. So I thought I would try and light from the bottom. I was 40 or 50 feet away and when i struck the lighter at ground level it rolled me 2 or 3 times. The vapors were laying on the ground. Not gonna do that again!
Anyway with 30 years of hunting with dogs (80 – 90 days annually) a low pressure is just a walk in the woods. Even a grouse spotted walking along a forest service road and 5 minutes later the dogs can’t take the track. On a high pressure they can take a 24 hour old track. When the scent is falling they do o good job of locating treed/roosting birds. Same goes with rabbit dogs, best beagles can’t run a rabbit 25 yards. Same with bear dogs unless the brush is dense and high, then it’s iffy after 10 minutes
If someone can explain my observations and smoke from a household chimney other than barometric pressure, I’m all ears or eyes on you. Better be a hell of a good explanation.

May 23, 2017 8:31 am

Somebody design expiraments and take data. I hate all this speculation.

Tom in Florida
May 23, 2017 8:42 am

Perhaps the headline should have been:
“Buzzards get high from grass”

May 23, 2017 9:19 am

A partial greenhouse effect… The tall standing grass inhibits the air convection rates at the ground which causes a build up of a thermal pocket of heated air. That air pocket then bubbles upward instead of mixing with the rest of the air. You can simulate this by setting up a stockade like fence in say a 5 x 5 or 10 x 10 ft square. Measure the temperature inside the fenced in area and take a measurement away from the enclosure say 20 feet.
While the heat entrapment in tall standing grass is not on the order of a real greenhouse because there is zero convection with the ambient air inside a greenhouse, the rate of convection is severely slowed.
BTW- the idea that the tall standing grass provides a greater surface area for heating probably helps a lot too, experimental PV solar panels use this same concept of nanopillars to absorb more sunlight.
The forest area while it may seem should provide the same effect as tall grass does not since surface area underneath the canopy is cool from shading, however, a somewhat open unobstructed surface on top the branches to allow mixing.

Ron Williams
May 23, 2017 10:01 am

I do know one thing…never pick a fight with a Murder of Crows. Or Ravens. Most intelligent birds out there IMO. And vindictive and never forget an incident or a person. I had a dust up with some noisy Ravens about 30 years ago at my farm at 5 Am in the morning. For the last 30 years, I have been the recipient of numerous ‘attacks’. One spring while away for a few weeks, the Ravens came to my patio deck and completely plucked out all the foam on two old Lazy Boys that I retired from the living room to outside since they were finished for inside use. I guess the foam probably makes very good insulation for a nice nest somewhere. Sure did look funny, two lazy boys side by side and all that was left were just spring coils and wood framing. Even took the faux leather.
The next year, they found my quad parked out in the woods one day where I was working, and they completely destroyed the seat and foam, again, while I was gone for only 3-4 hours doing some forestry cruising. And they were sitting in trees watching me when I came back, ‘laughing’ at me.
A few years back, I came back from town in winter with a dozen 2 pound frozen lasagna in the back of the truck box. After just an hour being away from the truck, all dozen lasagna’s were completely gone, except for the packaging. How they got all that frozen brick lasagna out and gone is beyond me. Wish I would have had a dash cam recording that. And many other such lesser events every year it seems, which I wonder if they live that long, or teach it to their new generations.
The lesson is, be careful who & what you pick battles about, because feuds seldom end. Especially with a Murder of Crows/Ravens. We are now just starting to make peace…slowly.
[Bears ate the lasagne? Raccoons perhaps? .mod]

Tom in Florida
Reply to  Ron Williams
May 23, 2017 10:22 am

One of the funniest things I have seen was a crow who had apparently been watching me eat a muffin while I was in a parking lot waiting for a ride. When I was finished I rolled up the muffin wrapper and tucked it inside a styrofoam coffee cup and wedged that into the baby seat of a shopping cart. After a while I walked away and when I looked back the crow came down from I don’t know where, plucked the styrofoam cup from the cart and pulled the muffin wrapper out, spread it out and began to pick at the crumbs. It was pretty cool to think that the little bastard saw what I did, figured out where the food was and waited until I was far enough away so I couldn’t bother him.

The Original Mike M
Reply to  Tom in Florida
May 23, 2017 11:46 am

Reply to  Tom in Florida
May 23, 2017 1:14 pm

Great story, Tom! 🙂

Ron Williams
Reply to  Ron Williams
May 23, 2017 3:54 pm

Funny you mention bears Mod… Last night at sunset I walked out the door where I have a semi remote acreage/hobby farm. Walked around a blind corner and there was a very large Brown bear right in the front yard 15 feet away, maybe a Grizzly cause it did have a small hump. 15 feet was all that separated me from being a tasty snack as I backed up real slowly. This Am, I go for a quad ride to check water levels at a dam behind my property, and there is 2 little bears off in the distance. A little unnerving for sure having a mother bear and cubs hanging around.
If I didn’t have electricity and Sat internet here, you would never know there was any environmental stress in the wilderness. It seems nature has never been so healthy. The conifer trees and especially broad leafed trees like Aspen and Cottonwood, (especially willows) are growing at rates unheard of. I assume it is the extra CO2 in the air since current growth exceeds anything in the records.
No, the truck box had ample evidence of Raven feathers, and they were all still hanging around when I got back to the truck wondering what I would leave hanging around outside next. Hopefully the bears and the Ravens don’t gang up on me…

The Original Mike M
May 23, 2017 11:39 am

FYI Willis – in case you ever move to Rochester MN – you will need to get a permit to allow grass to grow that high.

48.05: Natural or Naturalistic Landscape Permits .
Natural or Naturalistic Landscape Permits are required if a proposed landscape includes grasses that exceed or are expected to exceed 12 inches in overall height. Permit applications shall be submitted to the Park Department.

May 23, 2017 4:44 pm

Well fed “buzzards” looking for a place to rest, with a thermal just in case a quick escape needed ?

Gras Albert
May 23, 2017 8:50 pm

Mike Borgelt, I still use a B50.
My 1000’s of hours of practical experiments in and observations on lower atmosphere physics (I, too, am a soaring pilot) would lead me to ask for for more information, e.g. Was the wind direction/strength typical or unusual on the day? Normally reliable thermal triggers can be masked by topographic down drafts when a normally into wind slope becomes a lee slope. Most likely, however, is that the day concerned simply had an unfavourable lapse rate. Temperature inversions kill thermals stone dead.
Philip Wills, another glider pilot, made a significant scientific contribution by establishing the manner in which South African vultures communicated the location of a meal leading to the frequently filmed sight of dozens of birds around a carcass. First, he realised the reason that vultures regularly left thermals shared with sailplanes at 2,500ft above the ground was eyesight related, much more than one half mile high and they couldn’t identify their next meal. Second, he realised that they flew in a grid pattern arranged like a honeycomb in which each bird could see multiple neighbours, each being around one half mile distant. When a vulture left the grid for a meal it’s neighbours would notice and fly toward its last known position expecting to join the feast. Meanwhile, the neighbours of the birds flying towards the missing bird would notice their missing neighbours and fly towards their next meal too, a true communication grid! Isn’t nature wonderful?

Danley Wolfe
May 24, 2017 11:07 am

Turkey buzzards and all similar beasties and birdies do not make days in advance flight plans. They continually move on trial and error making instantaneous adjustments based on short term feedback on “how it’s going at the moment.” They don’t think about this much at all. Unlike the climate gestapo they do not often fool themselves by deeply ingrained falsehoods that fit some ideological preconditioning.

ken morgan
May 25, 2017 3:28 am

no need to worry about grass we will be all drowned

Charles Greenlaw
May 26, 2017 9:40 pm

Willis, the setting for your wonderful tale is right out of a 1950’s juvenile and construction crew joke, which included in its dialogue the snooty butler’s reply to the rabbit who came calling at his friends’ mansion, “Mister Buz-ZARD is out by the yard!” … (“And Mister Tur-TELL is down by the well!”)

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