News Release 4-Dec-2019
Migratory birds shrinking as climate warms, new analysis of four-decade record shows
University of Michigan
ANN ARBOR–North American migratory birds have been getting smaller over the past four decades, and their wings have gotten a bit longer. Both changes appear to be responses to a warming climate.
Those are the main findings from a new University of Michigan-led analysis of a dataset of some 70,000 North American migratory birds from 52 species that died when they collided with buildings in Chicago.
Since 1978, Field Museum personnel and volunteers have retrieved dead birds that collided with Chicago buildings during spring and fall migrations. For each specimen, multiple body measurements are made.
The research team analyzed this remarkably detailed dataset to look for trends in body size and shape. The biologists found that, from 1978 through 2016, body size decreased in all 52 species, with statistically significant declines in 49 species.
Over the same period, wing length increased significantly in 40 species. The findings are scheduled for publication Dec. 4 in the journal Ecology Letters.
“We had good reason to expect that increasing temperatures would lead to reductions in body size, based on previous studies. The thing that was shocking was how consistent it was. I was incredibly surprised that all of these species are responding in such similar ways,” said study lead author Brian Weeks, an assistant professor at the U-M School for Environment and Sustainability.
The senior author is Benjamin Winger of the U-M Department of Ecology and Evolutionary Biology and the Museum of Zoology. Weeks worked on the project as a postdoctoral researcher in Winger’s lab. Co-authors include David E. Willard, the Field Museum ornithologist and collections manager emeritus who measured all 70,716 birds analyzed in the study.
The new study is the largest specimen-based analysis of body-size responses to recent warming, and it shows the most consistent large-scale responses for a diverse group of birds, Weeks said.
Several lines of evidence suggest a causal relationship between warming temperatures and the observed declines in avian body size, according to the researchers. The strongest evidence is that–embedded within the long-term trends of declining body size and increasing temperature–there are numerous short-term fluctuations in body size and temperature that appear to be synchronized.
“Periods of rapid warming are followed really closely by periods of decline in body size, and vice versa,” Weeks said. “Being able to show that kind of detail in a morphological study is unique to our paper, as far as I know, and it’s entirely due to the quality of the dataset that David Willard generated.”
“It’s really been a herculean effort on the part of Dave and others at the Field Museum, including co-author Mary Hennen, to get such valuable data from birds that might otherwise have been discarded after they died from building collisions,” Winger said.
Within animal species, individuals tend to be smaller in warmer parts of their range, a pattern known as Bergmann’s rule. And while the possibility of body size reduction in response to present-day global warming has been suggested for decades, evidence supporting the idea remains mixed.
The uncertainty is likely due, in part, to the scarcity of datasets like the Field Museum trove.
For each bird, Willard measured the length of a lower leg bone called the tarsus, bill length, wing length, and body mass. In birds, tarsus length is considered the most precise single measure of within-species variation in body size.
The data analysis revealed that:
- Three measures of body size–tarsus length, body mass and PC1, a common measure of overall body size that combines several key body-part measurements–showed statistically significant declines. Tarsus length declined 2.4% across species.
- Wing length showed a mean increase of 1.3%. Species with the fastest declines in tarsus length also showed the most rapid gains in wing length.
- Mean summer temperature was significantly negatively associated with bird body size–meaning that body size decreased significantly as temperatures warmed. Temperatures at the birds’ summer breeding grounds north of Chicago increased roughly 1 degree Celsius (1.8 degrees Fahrenheit) over the course of the study.
Studies of plant and animal response to climate change often focus on shifts in the geographical range of a species or the timing of events such as springtime flowering and migration. The consistency of the body-size declines reported in the new study suggests that such changes should be added to the list of challenges facing wildlife in a rapidly warming world, Weeks said.
“It’s clear that there’s a third component–changes in body size and shape–that’s probably going to interact with changes in range and changes in timing to determine how effectively a species can respond to climate change,” he said.
Long-distance bird migration is one of the most impressive feats in the animal kingdom. The extreme energetic demands of flying thousands of miles have shaped the morphology of migrating birds–their form and structure–for efficient flight.
The authors of the Ecology Letters paper suggest that the body-size reductions are a response to climate warming and that increased wing length may help offset the body-mass losses.
The researchers plan to test that idea in a follow-up project, which will again make use of the Field Museum dataset. They’ll also look further into the mechanism behind the body size and shape changes and whether they are the result of a process called developmental plasticity, the ability of an individual to modify its development in response to changing environmental conditions.
The birds analyzed in the study are small-bodied songbirds that breed north of Chicago in the summer and migrate through the region in high numbers. Several species of sparrow, warbler and thrush make up the majority of the dataset, with thousands of individuals of each species documented as lethal collisions.
The observed changes in avian body size and shape are subtle–at most a couple grams’ difference in body mass and a few millimeters in wing length–and are not detectable with the naked eye. The Field Museum bird collision dataset highlights the value of natural history museum specimen collections, which help scientists understand how nature changes through time, the authors note.
“When we began collecting the data analyzed in this study, we were addressing a few simple questions about year-to-year and season-to-season variations in birds,” said the Field Museum’s Willard. “The phrase ‘climate change’ as a modern phenomenon was barely on the horizon. The results from this study highlight how essential long-term data sets are for identifying and analyzing trends caused by changes in our environment.”
###
The authors of the Ecology Letters paper, in addition to Weeks, Winger, Willard and Hennen, are Marketa Zimova of the Institute for Global Change Biology at the U-M School for Environment and Sustainability, former U-M undergraduate Aspen A. Ellis, and Max L. Witynski of the Field Museum.
Funding for the study was provided by the Field Museum and the University of Michigan’s Department of Ecology and Evolutionary, Museum of Zoology, and Institute for Global Change Biology.
More information: April 2019 Michigan News release about nocturnal flight calls and building collisions.
Image link: https://drive.google.com/drive/folders/1u6DxrzXGE7bk48Vi_DefaX_W2eBkwxvs
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
And where is the discussion on the massive displacement of native flora/fauna with many invasive species.
Company I worked for took the 40 acres in front of the office plant and training center and planted native grass and flowers as recommended by the university agriculture department. Took over three years to displace all of the invasive plants. When fully restored it was obvious that the fauna numbers had increased. It is clearly obvious that this area is different than the other acerage. When the seeds and the insects attracted by the native plants that birds eat are now longer growing they need to find something else.
Wing length is usually closely connected with migration distance, so the most likely explanation is that the birds are either breeding further north, or wintering further south than before.
Which could be due to either climate change or changes in land use (e g deforestation in the breeding areas and/or wintering areas).
The problem is not the study, the observations, or necessarily the conclusions (e.g. frame of reference, including period). The problem is the imputed negative connotation to “climate change” forced by sociopolitical adventurism, including: sociopolitical exemptions to favored industries, calls for redistributive change, extrajudicial stalking, legal harassment, bigotry, etc. People are, with cause, progressively skeptical of methods and motives.
It appears that birds are only adapting to adjusted data. When I go to Tony Hellers site and look at temperature data I don’t find any correlation.
Conclusion: Quit adjusting the data and birds will adapt to the new data record.
This could be another polar bear: correct observation(s), wrong conclusions. The use of correlation can lead to false conclusions in a chaotic (e.g. evolutionary) system. Combined with sociopolitical adventurism, and the responses will become progressively skeptical, even dismissive.
The University of Michigan could probably have found an even bigger and more representative selection of specimens to study, by looking around the bases of Wind-Turbines and under concentrating solar stations. The birds that hit buildings in Chicago, may have been a selection of sillier birds who were not looking where they were going. Those under the renewable choppers were completely taken by surprise.
The birds that moult all feathers in their 1st year essentially end up as adults with the same wing length. It is birds that do not fully moult in their first year & keep some of their immature plumage that have end up with lengthier wings as adults.
1st winter birds (juveniles) of the same kind that are larger tend to be males. Those males as adults end up larger than their contemporary adult females.
Point being: I am not sure if the original post’s cited report controlled for variables such as whether comparing the same kind 1st year & 2nd year birds, or whether the same kind if bird comparison accounted for male & female variability.
Bird population decline is based on a variety of factors. How many were chopped up by the installation of 350,000 wind turbines globally over the last four decades? We don’t know because only Hawaii requires bird and bat mortality reporting and any attempt to determine that number will result in wind industry lawsuits to avoid divulging it. We could collect a larger sample size by collecting under the turbines but the wind industry will not allow it. For a discussion of these issues read Kenn Kaufman’s book “A Season on the Wind.”
Sounds like migratory birds can now be the new proxy for earth temperature measurements. When will Michael Mann come out with his latest earth temperature reconstruction?
From the article: “ANN ARBOR–North American migratory birds have been getting smaller over the past four decades, and their wings have gotten a bit longer. Both changes appear to be responses to a warming climate.”
Well, that can’t be possible because the climate warmed during the 1930’s right up to the same level of warmth as today, and the birds didn’t shrink back then, so it must be something else that is affecting these birds. Perhaps these are adaptions by the birds to dodging windmill blades. 🙂
If the climate is getting warmer then the birds that used to migrate due to cold weather don’t have to migrate. These “scientists” need to ask more outside the CLIMATE CHANGE box
With a million possible causes for a nearly imperceptible change in suicidal Chicago inner city bird BMI, I’ll bet they never seriously considered anything other than globe-a-warmin’.
“I’ll bet they never seriously considered anything other than globe-a-warmin’.”
That’s where the money’s at.
There are a lot more tall buildings in Chicago now than there were a half century ago. Ya think maybe that the fat birds with stubby wings might have gotten killed off from running into them early on?
This is the most ridiculous fear mongering I have yet to see. I monitored bird populations for over 20 years, measurring weights, wing lengths and tarsi lengths. An average sparrow’s tarsus lengths such as a Song Sparrow’s measures about 26 mm. It varies with subspecies. There about 9 subspecies breeding in California alone. According to this bogus report, birds are “shrinking” based on on a 2.4% reduction in the tarsus length. 2.4% 0f 26 mm is about 0.6 mm, typically a measurement that is beyond the precision of the tools employed. The accuracy in measurements of tarsi can easily vary by 1 to 2 mm. Furthermore there is no reason to believe that a bird’s tarsus length would be affected by climate or such a change means bias are shrinking. But the media loves such BS. Much more likely is the fact that subspecies tarsus lengths vary and the reduction determined by averaging many species is an artifact of avearging many species and subspecies migrating through Chicago.
Good points. Climate alarmists use temperatures with a +/- 0.5 degC error interval and average them to come up with temperatures supposedly accurate to the hundredth or thousandths of a deg. This is the same idiocy you point out, ” typically a measurement that is beyond the precision of the tools employed.”.
It makes one wonder exactly what is being taught to students today!
I’ve a bunch of wild birds who accept food from my hand. They thrive, and tend to be larger than other completely wild members of their species.
The other variable is nesting sites.
If nesting sites and abundant food are available you get lots of big wild birds.
So if ‘global warming’ occurs (which so far it seems not to have, at least this century) then birds should do OK. More food. Except that people are taking their nesting sites and building great big fly swats called ‘wind turbines’.
Oh, the buzzards in the sky get so dizzy they can’t fly just from sniffin’ that good old mountain dew.
Canada geese, snow geese, gray geese, teal, mallard, Ruddy, canvasback, coots, blue heron, Sandhill cranes, and, get this, Whooping cranes. I see them all during the great migration of avian species escaping, fleeing, none other than cold weather. The warm is gone, the seasons change, cold forces action. You take flight, a warmer place is the place to be. Thirty below zero has a direct effect on your chances of survival. believe it or not.
Whooping cranes fly directly above where I am in late September. Less than 500 feet right above my head. They’re out in the creek at times resting up for the next leg of the migratory flight. This year, the number of whoopers observed was twelve, probably were some more, just didn’t see them. They migrate with the Sandhill cranes, both can fly more than a mile high, you’ll see them if you can spot them that far up in the sky. Incredibly smart birds, Whooping cranes and Sandhills both.
They’ll all be moving on, south is the destination, anywhere away from the cold. It is a natural phenomena, seek warmth, you have to do what keeps you alive. Cold can be a killer. Nunavut is no place to be in January, just the way it is.
A shortage of western meadowlarks, not that many, but I do hear them during the summer months, they’re not gone. Habitat is going to determine where they go. Urban spaces are not a place for meadowlarks. The word ‘meadow’ is the key word here.
Upland game, they’re out there, but you can’t hunt them, the numbers are dwindling. Stopped hunting grouse about forty years ago, shot one back in 1980, last one. In the mid-sixties, partridge were everywhere, shooting ducks in a pond. No more, hunted to a threatened population. Doves seem to survive okay. Pheasant numbers remain strong. Don’t hunt them though, could, but don’t. Pigeons are there and can be harvested if I want one or two. Too many hunters, not enough upland game, it will take a toll. The Passenger pigeon wasn’t so lucky.
Owls are around, bald eagles, red-tail hawks, falcons, kites, gulls, orioles, sparrow, finches, barn swallows, robins, blue jays, all out there. The doggone woodpeckers don’t stop when they are rattling away of some cottonwood branch. Depends upon the time of year. Hummingbirds, check. Usually, hummingbirds and bald eagles hunt in tandem. Just kidding.
A bird population estimated at 20 billion for the North American continent alone, the estimated number, anyhow. Got to have hatched chicks, you’ll lose a lot of birds if there are no eggs to hatch, doesn’t matter the species.
All hatched birds will die, don’t need to be chopped out of the sky by some predatory wind turbine. It is not right, an outrage.
May the Bird of Paradise fly up your nose.
I have a different hypothesis. I think they’ve gotten smaller because of the number of television screens per household, which has exploded since 1979.
It would be interesting to see if the samples from a cold decade (say the 1970s) were any larger than the warmer decades before and after. Bergman’s Law on average size versus average temperature seems to be kicking in awfully fast given the rather marginal change in temps. The pressure to find a climate-related angle on so many scientists makes me a tad skeptical of a significant 2% change when anything less would probably not be publishable.
Small migratory birds (e.g. warblers) are mostly insectivores. Changes in pesticide use over time make for better feeding and so smaller ( presumably weaker) birds can survive and thus lower the average size.
There is also the issue of collection uniformity. I saw a report of a similar study comparing carcasses of modern birds to 19th-century museum bird specimens in which the more robust samples were likely selected. Birds who collapse, make navigation errors etc are likely to include sicklier members. If instead, the scientists hit a migrating flock at the same time every year with a random shotgun blast….(not advocating, just saying).
If this is already almost a law in the warmer areas of their habitat, I’m not sure this is any revelation at all.
The assumption that the birds collected after hitting windows in Chicago represent a random sampling of the entire migratory bird population is the major assumption that needs to be tested and tested and tested. As always, lets look at the data, including things like location of collection and the local architecture/geography. Did the numbers suddenly shift when one building was torn down and a new building put up? Have prevailing winds been from a different direction for a few critical years blowing different sized birds off course than in subsequent years? Have changes in windows reflectivity had an affect. I am not an ornithologist, and this took me 15 seconds to come up with. Science is all about trying to destroy your own hypothesis, and being pleasantly surprised, from time to time, when one survives all your attempts to kill it off.
They are just rewording bergmann’s rule with climate change. I learned this rule in my evolutionary biology class when I was working on my PhD in zoology. A recent paper questions this hypothesis and it has some very interesting conclusions. No general relationship between mass and temperature in endothermic species
Kristina Riemer,1 Robert P Guralnick,2 and Ethan P White1,3. Its on PubMed
Abstract
Bergmann’s rule is a widely-accepted biogeographic rule stating that individuals within a species are smaller in warmer environments. While there are many single-species studies and integrative reviews documenting this pattern, a data-intensive approach has not been used yet to determine the generality of this pattern. We assessed the strength and direction of the intraspecific relationship between temperature and individual mass for 952 bird and mammal species. For eighty-seven percent of species, temperature explained less than 10% of variation in mass, and for 79% of species the correlation was not statistically significant. These results suggest that Bergmann’s rule is not general and temperature is not a dominant driver of biogeographic variation in mass. Further understanding of size variation will require integrating multiple processes that influence size. The lack of dominant temperature forcing weakens the justification for the hypothesis that global warming could result in widespread decreases in body size.
Rotter, birds have to acquaint modern live and renewability:
https://www.google.com/search?q=solar+power+plant+burns+birds&oq=solar+power+plants+birds+burning+&aqs=chrome.