Migratory birds have lighter-colored feathers

Date:
December 6, 2021
Source:
Cell Press
Summary:
Migratory birds are specially adapted to find their way over
extreme distances that represent remarkable tests of endurance. Now,
researchers have discovered an unexpected way that migratory birds
keep their cool during such arduous journeys: lighter-colored
feathers.



FULL STORY ========================================================================== Migratory birds are specially adapted to find their way over extreme
distances that represent remarkable tests of endurance. Now, researchers reporting December 6 in the journal Current Biology have discovered an unexpected way that migratory birds keep their cool during such arduous journeys: lighter- colored feathers.


==========================================================================
"We found across nearly all species of birds, migratory species tend to
be lighter colored than non-migratory species," said Kaspar Delhey of
the Max Planck Institute for Ornithology, Seewiesen, Germany. "We think
that lighter plumage coloration is selected in migratory species because
it reduces the risk of overheating when exposed to sunshine. Lighter
surfaces absorb less heat than darker ones, as anybody wearing dark
clothes on a sunny day can attest! This would be particularly important
for long-distance migrants that undertake extensive flights during
which they cannot stop to rest in the shade." Delhey and colleagues had
been studying the effects of climate on bird coloration. Their earlier
studies showed that, in general, lighter colored birds are found where temperatures are high and there is little shade.

Presumably that's at least in part because the birds' lighter plumage
helps to keep them cooler in the hot sun. Around that same time, the researchers came across studies by others showing that some birds fly
at much higher altitudes during the day compared to at night.

"Because flying at high altitude is likely costly, these changes required
an explanation," Delhey says. "One possibility was that flying higher,
where it is colder, would offset the heat absorbed by the plumage when
the sun was shining." If so, they realized, another way to reduce the
risk of overheating would be to absorb less solar radiation in the first
place. It raised a question: have migratory species evolved lighter
feathers? To find out, they quantified overall plumage lightness (from
0 = black to 100 = white) for all bird species, using bird images from
the Handbook of the Birds of the World. Next, they compared the data on coloration with the species' migratory behavior, while controlling for
other factors known to effect plumage color.

Overall, the findings show that bird species get increasingly lighter
as they migrate more. So, resident birds tend to be darker than
short-distance migrants. Short-distance migrants are darker than bird
species that travel farther. Delhey said that the one of the biggest
surprises was how consistent the effect was across different types of
birds. They saw the same pattern in birds large and small. The same held
true in waterbirds and land-dwelling birds, too.

The findings are another reminder of the important role of temperature
and climate factors more broadly in shaping the evolution of animal
coloration.

They also have clear implications for understanding the impacts of
global warming and potential adaptive evolutionary responses, the
researchers say.

Delhey notes that many factors influence bird coloration and light colors
are but one of many ways that migratory birds can avoid overheating. His
team will continue exploring the connections between migration,
climate, and other selective factors that shape the evolution of plumage
colors in birds. They also suggest, in light of the new findings, that
future studies should directly test how migratory species cope with thermoregulatory challenges.

========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Kaspar Delhey, James Dale, Mihai Valcu, Bart Kempenaers. Migratory
birds
are lighter coloured. Current Biology, 2021; 31 (23): R1511 DOI:
10.1016/ j.cub.2021.10.048 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211206113009.htm

--- up 2 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)