- Migrating birds have adapted to climate change by shrinking, with smaller bodies and shorter legs offset by longer wings.
- The Field Museum collected over 70,000 birds killed mostly in building collisions, painstakingly measured every one, and built an almost unprecedented data set.
- While scientists work to mitigate bird deaths from manmade structures, this is a rare silver lining.
Birds are getting smaller, and scientists attribute it to climate change. University of Michigan researchers analyzed a data set measured from migrating birds over the last 40 years—over 70,000 birds in total—which shows that their bodies are getting smaller while their wings are getting bigger.
One scientist at Chicago’s Field Museum measured each of the 70,000 birds over 40 years. The museum collects the birds that have struck buildings and died; nearly a billion birds die each year when they fly into windows they can’t really see, and glass-sided buildings like Chicago’s Hancock Center and Willis (Sears) Tower are one of the biggest categories for bird destruction.
But the silver glass lining is the Field Museum’s determined volunteers have turned bad news for birds into good news for bird research. Measuring birds, especially in wild populations, is daunting and thus done infrequently. Scientists don’t have firm theories or explanations for changes in birds over time.
“The uncertainty is likely due, in part, to the scarcity of datasets like the Field Museum trove,” the press release states. The Field Museum boasts one of the most robust collections of preserved birds and eggs in the world, dating back to its first exhibition at the 1893 World’s Fair.
Why has climate change motivated birds to grow smaller over time? The Field Museum data covered 52 species that all migrate, and migrating birds all undergo drastic physical stress during annual trips that top out at 44,000 miles for the Arctic tern. Like hibernating animals or spawning salmon, birds must accumulate enough body mass to last them during an extended time without regular nutrients. In humans, exercising without enough calories causes muscle breakdown.
As the climate warms, birds might shrink because their body temperatures require less regulation or insulation. But that means their metabolism must work even harder to power their wings, especially for migrating birds. The Michigan researchers analyzing the Field Museum data suggest birds have grown longer wings to compensate.
“We hypothesise [sp.] that increasing wing length represents a compensatory adaptation to maintain migration as reductions in body size have increased the metabolic cost of flight,” they write. In other words, if it’s going to cost proportionally more to flap the wing, you might as well make the wing as long as possible and get the most bang for your caloric buck.
The study is also long enough that researchers noted an overall nearly 2 degrees Fahrenheit increase in summer temperatures where the birds breed. Because of the observed link between body size and increasing temperature, the scientists feel comfortable suggesting more research into this as a climate-change coping mechanism that other scientists should prepare for.
“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,” the press release says.
The Michigan team plans to continue studying the Field Museum dataset as a next step in its research into bird morphology over time. Emeritus collections manager David Willard, who documented every one of the 70,000 birds, has been at the Field Museum since 1976. The collection and measurement of these birds isn’t even the bulk of his life’s work, which also involves international tropical birds and research trips around the world.
You Might Also Like