Nav: Home

Camouflage influences life-and-death decisions that animals make

June 09, 2016

Nesting birds time their escape from an approaching predator depending on how well camouflaged their eggs and their own bodies are, researchers from the University of Exeter and the University of Cambridge have discovered.

This is the first study to show that the camouflage of an animal or that of its offspring can explain the variation in risk-taking behaviour when approached by a predator.

Researchers worked with a team of skilled local assistants in Zambia to find the nests of several species of ground-nesting birds. Once a nest was found they monitored its progress, recording the escape distance of the adult bird each time they approached and, using camera traps, identified key predators such as banded mongooses, vervet monkeys and grey-headed bush shrikes -- and even human children.

In complex environments it is hard for animals to perfectly match their background. When an animal's camouflage is poor it has a higher risk of being detected and eaten by a predator, so it should more readily flee from an approaching threat. The researchers therefore set out to test whether the distances at which birds fled from their nests on the exposed ground was related to the camouflage of their plumage and eggs.

They found that birds that usually flee from predators at long range, such as plovers and coursers, stayed on their nest for longer when the pattern of their eggs was a better match to the background. They also adjusted their behaviour in the heat of the middle of the day, letting a predator approach a little closer before fleeing. This probably allows them to shade their eggs for as long as possible, and so reduce the chance of them cooking in the African sun. By contrast, another group of birds, the nightjars, usually sit tight as predators approach so that their eggs are concealed by their camouflaged bodies until the last minute. Sure enough, nightjars stayed on their nests longer when the colour and pattern of their own plumage, rather than that of their eggs, was a better match to the background.

The team photographed the adult birds and eggs using specially-calibrated digital cameras. Sophisticated computer models of animal vision were used to map images to each predator's visual abilities. Birds have high colour sensitivity and can see ultra-violet wavelengths. The banded mongoose has relatively poor colour vision and can only see colours equivalent to blues and yellows.

Study author, Jared Wilson-Aggarwal, a PhD researcher at the University of Exeter's Environment and Sustainability Institute, said: "Plovers, coursers and nightjars nest on the bare ground during the Zambian dry season. Temperatures can get very high and if approached by a predator the adult bird has to make a hard decision to either, sit tight and continue shading their eggs or to flee the nest and prioritise their own survival."

"Our results suggest that camouflage is able to mitigate not only predation risk but also thermal risks, by permitting adults to shade their eggs for longer when the risk of them overheating is highest."

Martin Stevens from the University of Exeter who, along with Claire Spottiswoode from the University of Cambridge, co-led the project said: "Our study shows how animals monitor their own camouflage and that of their offspring, and use this to guide how they behave. It complements a small but growing number of studies showing how important behaviour is in facilitating camouflage in nature."

Claire Spottiswoode from the University of Cambridge added, "Fifty years ago, the pioneering ecologist David Lack predicted that birds with camouflaged plumage should benefit most from sitting tight on their eggs until the very last minute. Nightjars are some of the most beautifully camouflaged animals in the world, and sure enough the African nightjars we studied often only fled their nests when we were at arm's length!"

Escape Distance in Ground-Nesting Birds Differs with Individual Level of Camouflage is published in the journal The American Naturalist
-end-


University of Exeter

Related Birds Articles:

Diving birds follow each other when fishing
Diving seabirds watch each other to work out when to dive, new research shows.
Why do birds migrate at night?
Researchers found migratory birds maximize how much light they get from their environment, so they can migrate even at night. 
How can robots land like birds?
Birds can perch on a wide variety of surfaces, thick or thin, rough or slick.
Is wildfire management 'for the birds?'
Spotted owl populations are in decline all along the West Coast, and as climate change increases the risk of large and destructive wildfires in the region, these iconic animals face the real threat of losing even more of their forest habitat.
Feathers came first, then birds
New research, led by the University of Bristol, suggests that feathers arose 100 million years before birds -- changing how we look at dinosaurs, birds, and pterosaurs, the flying reptiles.
First birds: Archaeopteryx gets company
Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich describe a hitherto unknown bird from the late Jurassic period.
Are coffee farms for the birds? Yes and no
Through painstaking banding of individual birds, Sekercioglu asked whether the expansion of coffee plantations is reducing tropical bird biodiversity.
Birds bug out over coffee
New research conducted by the University of Delaware has found that birds are as picky as coffee snobs when it comes to the trees they'll migrate to for a summer habitat.
Speciation: Birds of a feather...
Carrion crows and hooded crows are almost indistinguishable genetically, and hybrid offspring are fertile.
How much rainforest do birds need?
Researchers of the Department of Conservation Biology at the University of Göttingen have carried out research in Southwest Cameroon to assess which proportion of forest would be necessary in order to provide sufficient habitat for rainforest bird species.
More Birds News and Birds Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.