A new study shows that migrating birds evolved lighter feathers in order to keep them cool when flying long distances.
Sanderlings, sandpipers, and other birds fly thousands of miles each year in search for the most ecologically sound habitats that will allow them to feed, breed and raise their young.
They are exposed to severe weather conditions and can overheat if they stay too much in direct sun.
New research by the Max Planck Institute for Ornithology, Germany, has shown that many species of migratory birds have developed pale plumage. This allows them to absorb less heat than darker feathers.
These birds have a lower risk of overheating when they’re exposed to the sun for extended periods.
Calidris alba sanderlings, a long-distance shorebird that migrates along the coast of Canada. They may be more comfortable being light-coloured in order to prevent overheating.
At least 4,000 species of bird are regular migrants – representing about 40 per cent of the world’s total.
To escape winter, many birds flock south from the far north, like Canada and Scandinavia.
About half of the species that migrate to temperate regions like the UK are swifts or cuckoos who can’t find enough food.
This study was led by Dr Kaspar delhey from the Max Planck Institute for Ornithology (Germany). It compared plumage color data of various birds with their migratory behavior.
The researchers quantified overall plumage lightness for all species from zero to 100 – or black to white – using images from the Handbook of the Birds of the World.
Researchers found that birds that migrate long distances have the most light-colored feathers than species that move short distances.
“We discovered that almost all bird species have migratory birds which are lighter than those of non-migratory origin,” Dr Delhey said.
“We believe that lighter plumage colors are better for migratory birds because they have a lower risk of sunburn.
Even nightingales, and even willow warblers that migrate to Africa from Europe in the winter have plumage of light brown or light green, respectively.
Sanderlings, which are long distance migratory shorebirds, breed in the Arctic and visit the UK in the winter – benefiting from their grey and white hue.
The longest North American migration of white-rumped sandpipers is over 2,500 miles. They sometimes fly from Arctic Canada to winter in southern South America – covering 2,500 miles without a rest.
‘Lighter surfaces absorb less heat than darker ones, as anybody wearing dark clothes on a sunny day can attest,’ said Dr Delhey.
“This is especially important for long-distance migrants who fly long distances and cannot rest in the shade.
Calidris fuscicollis, a flock of mostly white-rumped Sandpipers. This is a long-distance shorebird that migrates to the Atlantic. It may be more comfortable being light-colored in order not overheat during migration.
Dr Delhey stated that one of the greatest surprises in the study was the consistency of the effects across all types of birds.
Researchers saw similar patterns in small and large species.
More evidence has been found that climate and temperature influences play an important part in the development of animal colors.
A previous study by Dr Delhey’s team revealed that lighter-coloured birds are found where temperatures are high and there’s little shade. The birds’ lighter plumage keeps them cool in the scorching sun.
Other studies also found that birds can fly much higher during daylight hours than night.
Dr Delhey stated that high-altitude flying is expensive and needed to be explained.
“One possible possibility is that you could fly higher and where the temperature is lower than the sun shines, to offset heat absorption by your plumage.
Dr Delhey recognized that there are many factors that influence the colour of birds, and that light colours can be used to avoid heat buildup in migratory birds.
In light of these new results, he suggests that future research be conducted to examine how migratory species deal with temperature regulation challenges.
This study was published in Current Biology on December 6, 2018.
WHY DO MIGRATING BIRDS FLY IN A V-FORMATION
The v-formation allows birds to fly higher and more efficiently.
Researchers discovered how migrating birds migrate by attaching tiny log devices to 14 northern balds ibises. These devices not only track their location and speed via satellite but also measure every flap on their wings.
The Waldrappteam in Austria, an Austrian conservation team that is working to bring northern bald ibeses back to Europe, hand-reared the 14 birds in this study.
To help birds fly efficiently and stay high, they use as much energy as possible. Stock image
As they flew with a microlight, the birds were observed as they flew along with it on their migration from Austria to Tuscany.
Professor Steve Portugal from the Royal Veterinary College (University of London) said that Dr. Portugal is the lead researcher. Although the V-formation of birds flocks has always fascinated researchers, it has remained elusive to date.
“The complex mechanisms of V-formation flight show remarkable awareness of the birds’ ability to react to their flock-mates’ wingpaths. Complex phasing strategies are evident in birds that have evolved V-formation to deal with dynamic wakes caused by flapping wings.
Scientists discovered that the V-shaped birds flew in an ‘in phase’ formation. This meant all their wing tips were following roughly the same route.
Each bird was able to get an extra boost from its neighbor in front.
Sometimes birds would fly directly between each other due to occasional shifts in their position.
To avoid getting caught in the downwash, birds changed their wingbeats to avoid being caught.