Via Eurekalert
Smithsonian scientists find declining rainfall is a major influence for migrating birds
Instinct and the annual increase of daylight hours have long been thought to be the triggers for birds to begin their spring migration. Scientists at the Smithsonian Conservation Biology Institute, however, have found that that may not be the case. Researchers have focused on how warming trends in temperate breeding areas disrupt the sensitive ecology of migratory birds. This new research shows that changes in rainfall on the tropical wintering grounds could be equally disruptive. The team’s findings are published in scientific journal Proceedings of the Royal Society B, March 30.
Many of the bird species that breed in the temperate forests, marshes and backyards of North America spend the winter months in the tropics of the Caribbean, and Central and South America. Insects are the primary food for many birds during the winter, and rainfall largely determines the amount of insects available. Climactic warming, however, is causing declining and more variable rainfall cycles in many areas, affecting the availability of insects and delaying when birds leave for their northern breeding grounds. To examine this, the Smithsonian scientists focused on American redstarts (Setophaga ruticilla), a member of the warbler family, at a non-breeding site in Jamaica where they conduct long-term studies.
“American redstarts were a perfect species for this study since they defend exclusive territories throughout the non-breeding period until they depart for spring migration and most return back to the same territory the following year,” said Pete Marra, research ecologist at the Smithsonian Conservation Biology Institute’s Migratory Bird Center. “These behaviors made it relatively easy to keep track of individual birds over multiple years and document changing spring departures. Each individual was fitted with a unique combination of colored leg bands.”
Precipitation in Jamaica is highly seasonal, with consistent rainfall from September to November and a pronounced dry season from January to March. The scientists observed the redstarts in their non-breeding territories for five years during the dry season. They paid special attention to the annual variation in dry season rainfall. The correlation between the amount of insects in a bird’s territory and the timing of its departure suggested to the team that annual variation in food availability was an important determining factor in the timing of spring migration. Had the redstarts relied on internal cues alone to schedule their spring departure, they would have all left their winter territories at the same time each year.
“Our results support the idea that environmental conditions on tropical non-breeding areas can influence the departure time for spring migration,” said Colin Studds, a postdoctoral fellow at the Smithsonian Conservation Biology Institute’s Migratory Bird Center and lead author of the study. “We found that the same birds changed their spring departure from one year to the next in relation to the amount of rainfall and food in March.”
During the past 16 years, the dry season in Jamaica has become both increasingly severe and unpredictable, leading to an 11 percent drop in total rainfall during the three-month annual drought. Making the future even more dire, climate models predict not only increased warming on temperate breeding areas but also continued drying in the Caribbean.
A critical question for the scientists is whether this variation in the onset of spring migration carries consequences for the birds. Delaying departure could be beneficial if food resources are low and the individual has not yet stored enough energy to migrate. However, delaying departure could affect arrival time to its breeding territory and result in less time to successfully reproduce. “Because American redstarts return to the same site to breed each year, arriving later may make it harder for them remain to remain in synch with their breeding cycle,” Studds said.
Such presumption that correlation is causation, as always in these climate studies.
We have migrating swallows in my area of Greece. They leave in October and return in the spring. Tradition has it that they return in March, even folk poems say so. I have not seen my first swallow yet. Does that mean it has been wet in Egypt?
Storms can destroy swarms. One October, driving in Crete I had to stop because the road surface was alive with swallows drying in the sun. A storm had passed and threw them to the ground. The ones that were over the sea would have drowned.
I would think that the birds would gauge the weather, probably sensing highs and lows, and time their departure with that. Storms can really drown them in the sea . There would be a correlation with wetness, they will leave early if it is dry, to get the good weather, which is another possible hypothesis/ factor entering in this correlation.
“Making the future even more dire, climate models predict not only increased warming on temperate breeding areas but also continued drying in the Caribbean.”
It sure was lucky that the Beagle happened to land in the only island group on the face of the earth that has variable local conditions, or else Darwin might never have noticed that species are capable of adaptation to geography and climate. [/sarc]
“Delaying departure could be beneficial ” … Beneficial because it has been so damn cold here in western Canada these past few springs that LBJs and SSBs that arrive early are killed by snow and cold. Snow and cold was so bad last year we lost over 90 percent of our Canada goose crop (eggs and goslings) on the ponds across the road from my house. Hardy geese!
And the robins will get hammered again this weekend by big snow dump!
I liked the old, warmer version of GW much more the colder version of warming … and I know the birds do as well.
@anna v:
Are those African or European swallows?
My head is spinning.
This report is based on the notion that climate warming is causing declining rain.
But last week someone explained all that extra snow we got this year was because climate warming caused MORE water vapor in the atmosphere which produced more snow.
anna v – Good point. Whenever I’m planning a flight the anticipated weather en route is always the deciding go/no-go factor.
Too bad that the birds were not flying sooner because then they could have just blamed global warming directly instead of having to resort to this kind of stretch.
Wow!
Changes in environmental conditions might cause changes in the behavior of migrating birds.
This is, indeed, incredibly insightful!
“Researchers have focused on how warming trends in temperate breeding areas disrupt the sensitive ecology of migratory birds.”
Not unless they are breeding in the heat sink cities. Of course “climate disruptions” can be blamed for changes in rainfall as well. Chalk another one up to CO2. It will never end until we take away the research funding.
From the main article:
Right, can’t have a study like that without mentioning a climax…and the climax is now history?
It sure is a good thing that birds who live on insects know how to get around by flying from a declining source of food to a more plentiful one. I would think that a few hundred kilometers here or there is by far not as much a problem for such birds as is their twice-annual migration of a few thousand kilometers.
Did the study examine that? Perhaps it was just a bit too cozy for the researchers to go into more rainy areas to check that out. After all, they would have become all wet doing that.
Amount of rainfall is a strictly local affair.
http://www.vukcevic.talktalk.net/Oxbridge.htm
Oxford and Cambridge are only 65 miles apart.
Wow, they say life began on earth 4.5 billion years ago, and so far everything has been fine.
It’s so sad to think that global climate disruption will bring that all to a close.
Declining rainfall?????
Impossible. We were just told this winter a warmer climate means a wetter climate.
This is just a guess, but an educated one, that somehow these birds survived the last ice age and the warming that followed it.
Maybe these ecologists issuing alarms are really Creationists at heart. Perhaps they think the World was created 6000 years ago just as it was in 1940 before we humans commited original sin through postwar industrializaiton. It would explain a lot.
“…During the past 16 years, the dry season in Jamaica has become…”
And the 16 years before that it was “normal”????
What about the 16 years before that, before that, before that….ad infinitum???
It sounds like we’re basing hysteria on a remarkably brief 16 year period, without mentioning an particular 16 year period in history with similar observations, and once again, the Models are like alarm sirens, but with no quantifiable reference, and no input of land use or other normal climate variation.
A critical question for scientists is whether this variation carries consequences???
Ya think?? The critical question should be how the birds have adapted in the past to shifts that were very likely much more severe, and part of the natural variability of climate.
Then go on to quantify exactly how much of the current change is anthropogenic….IF any.
An 11% decline in precipitation over 16 years does not sound like anything but normal variability.
If this species is vulnerable to that sort of decline in precipitation it would have been extinct long ago.
“The scientists observed the redstarts in their non-breeding territories for five years during the dry season. ”
Five years? Well that’s all settled then. This paper suggests precipitation patterns in Jamaica may be just a tad more complicated than these folks seem to assume.
http://people.uncw.edu/gambled/2008gamblecurtis.pdf
Wow. Its almost like over thousands of years mother nature may have evolved a system where the birds will not migrate to their breeding grounds as quickly and therefore may have reduced winter #’s when drought may reduce the available food the next winter. Something must be done to overcome this immediately or we will lose traction of humans can control everything on the planet.
“Making the future even more dire, climate models predict not only increased warming on temperate breeding areas but also continued drying in the Caribbean.”
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I was waiting for the global warming hook and they didn’t disappoint. Twenty years ago this would have just been an interesting biological observation. Today it can be passed off as a “significant finding” because of the threat of global warming. Then they had to repeat was “climate models predict”. Perhaps I’m cynical, but bird watching in Jamaica during the winter doesn’t seem like a bad gig. Obviously “more study is needed”.
You just know that AGW was worked into the grant proposal for this study.
So the birds have evolved the ability to sync their life cycle with a varying climatically regime. Why would they have done that? Either they anticipated mankind changing thins, or (now don’t laugh) maybe the climatic regime is naturally variable.
Climactic warming?
BTW “Smithsonian” and “Scientist” don’t belong in the same sentence.
Gosh-another “team” finding of a dire problem due to (term now not used) global warming. It never ends. No humming birds in my area of S. Ala. yet. Is it wet or dry in S. America where they migrate from or do they know the weather up in the states is still too cold for them yet. A friend of mine sailing in the middle of the Gulf of Mexico had a flock of them rest on her sailboat masts on their way somewhere in the fall . They must have been taking a shortcut across the Gulf instead of going across Central America. I propose a new study(fully funded of course) to look into the path of humming birds and I think somewhere in the Keys would be a great place for “team” headquarters and only a 5 year study for the “team” to start sounds about right.
“Making the future even more dire, climate models predict not only increased warming on temperate breeding areas but also continued drying in the Caribbean.”
Really, a model predicts increased warming, and continued drying? Well it must be true… Until is isn’t, but then of course a new model will surface that predicted that very thing the whole time…
Of course, all the money spent on demonizing a trace gas, that if it was eliminated would kill us all is beside the point. I wonder how many studies there have been about the harm that progressive policies cause by diverting resources away from real world problems.
Billions of tax dollars down the drain to show migratory birds can predict climate better than climate models.
These migratory birds produce huge volumes of CO2 in relation to their size during their annual migrations. We need to tax this CO2 and thereby reduce the unnecessary migration, to slow the rate of climate change in Jamaica.
Like people, birds should not be allowed to cross borders without passports and proof of resources. They are fair-weather freeloaders. Traveling here without permission and taking the food from our local birds. It is high time someone built a fence and kept them back where they belong.
It’s an indecreasing floodrought! Run! Stand still! Go backwards! Go south! Go north! Burrow deeper! Fly higher! Turn inside out! Apply the precautionary principle and do everything at once while doing nothing at all!