Higher elevation birds sport thicker down
Date:
February 15, 2021
Source:
Smithsonian
Summary:
A new study examines feathers across 249 species of Himalayan
songbirds, finding that birds at higher elevations have more of
fluffy down than lower elevation birds. Finding such a clear pattern
across many species underscores how important feathers are to birds'
ability to adapt to their environments. Furthermore, finding that
birds from colder environments tend to have more down may one day
help predict which birds are vulnerable to climate change simply
by studying feathers.
FULL STORY ========================================================================== Feathers are a sleek, intricate evolutionary innovation that makes
flight possible for birds, but in addition to their stiff, aerodynamic
feathers used for flight, birds also keep a layer of soft, fluffy down
feathers between their bodies and their outermost feathers to regulate
body temperature.
========================================================================== Using the Smithsonian's collection of 625,000 bird specimens, Sahas
Barve, a Peter Buck Fellow at the Smithsonian's National Museum of
Natural History, led a new study to examine feathers across 249 species
of Himalayan songbirds, finding that birds living at higher elevations
have more of the fluffy down - - the type of feathers humans stuff their jackets with -- than birds from lower elevations. Published on Feb. 15 in
the journal Ecography, the study also finds that smaller-bodied birds,
which lose heat faster than larger birds, tend to have longer feathers
in proportion to their body size and thus a thicker layer of insulation.
Finding such a clear pattern across so many species underscores how
important feathers are to a bird's ability to adapt to its environment
and suggests that adding down may be a strategy common to all songbirds,
or passerines as they are known to researchers. Furthermore, finding that
birds from colder environments tend to have more down may one day help researchers predict which birds are most vulnerable to climate change
simply by studying their feathers.
"The Himalayas are seeing some of the fastest rates of warming on
Earth," Barve said. "At the same time, climate change is driving an
increase in the frequency and intensity of extremely cold events like snowstorms. Being able to accurately predict the temperatures a bird
can withstand could give us a new tool to predict how certain species
might respond to climate change." The research was inspired by a
tiny bird called a goldcrest during a frigid morning of field work in
the Sho-kharkh forest of the Himalayas. Barve found himself wondering
how this bird, which weighs about the same as a teaspoon of sugar, was
able to flit about the treetops in icy air that was already numbing his fingers. Shoving his hands back into the pockets of his thick down jacket,
the question that formed in Barve's mind was "Do Himalayan birds wear
down jackets?" To answer that question, Barve and his co-authors used a microscope to take photos of the chest feathers of 1,715 specimens from
the Smithsonian's collections representing 249 species from the cold, high-altitude Himalayan Mountains. Then, Barve and his co-authors used
those super-detailed photos to determine exactly how long each feather's
downy section was relative to its total length. The team was able to
do that by looking at the fluffy downy section of each feather close to
its base when compared to the streamlined ends of most birds' feathers.
========================================================================== After meticulously logging the relative lengths of all those downy
sections, Barve analyzed the results and found that the smallest birds
and the birds from the highest elevations, where temperatures are at
their coldest, tended to have the highest proportion of down on their body feathers. The analysis showed that high-elevation birds had up to 25% more
down in their feathers, and the smallest bird had feathers that were three times as long as the largest birds, proportionately to their body size.
Past research suggested that birds from colder habitats sported added
downy insulation, but Barve said this is the first study to analyze
this pattern for such a large number of species in cold environments
and across 15,000 feet of elevation.
"Seeing this correlation across so many species makes our findings more
general and lets us say these results suggest all passerine birds may
show this pattern," Barve said. "And we never would have been able to
look at so many different species and get at this more general pattern
of evolution without the Smithsonian's collections." Carla Dove,
who runs the museum's Feather Identification Lab and contributed to
the study, said she was excited to work together with Barve to use the Smithsonian's collections in a new way. "Sahas looked at more than 1,700 specimens. Having them all in one place in downtown Washington, D.C.,
as opposed to having to go to the Himalayas and study these birds in
the wild, obviously makes a big difference. It allowed him to gather
the data he needed quickly before the COVID lockdowns swept the globe,
and then work on the analysis remotely." Barve said he is following
up this study with experiments looking into just how much insulation
birds get from their feathers and then will tie that to the feather's
structure and proportion of down. One day, Barve aims to develop a
model that will allow scientists to look at the structure of a feather
and predict how much insulation it gives the bird -- a capability that
could help researchers identify species vulnerable to climate change.
Dove said the potential to use these results to eventually understand how
some birds might cope with climate change highlights the importance of
museum collections. "We have more than 620,000 bird specimens collected
over the past 200 years waiting for studies like this. We don't know
what our specimens will be used for down the line; that's why we have to maintain them and keep enhancing them. These specimens from the past can
be used to predict the future." Funding and support for this research
were provided by the Smithsonian.
========================================================================== Story Source: Materials provided by Smithsonian. Note: Content may be
edited for style and length.
========================================================================== Journal Reference:
1. Sahas Barve, Vijay Ramesh, Toni M. Dotterer, Carla
J. Dove. Elevation and
body size drive convergent variation in thermo‐insulative
feather structure of Himalayan birds. Ecography, 2021 DOI:
10.1111/ecog.05376 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/02/210215092430.htm
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