The old saying, “Don’t put all your eggs into one basket” belies the very thing that many bird species must do. For this reason, predation is a major cause of loss of eggs, nestlings and the brooding hen, especially for birds that build open-cup nests. So how do birds protect their nests from predators?

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If you’ve ever tried to find a bird’s nest, then you know that birds are very clever at camouflaging their nests. But is nest camouflage an accident -- nest materials are part of the environment and so they should blend in after all -- or is it intentional?



A research team at the University of St Andrews in Scotland decided to find out by studying nest materials choices made by zebra finches, Taeniopygia guttata. Endemic to Australia, these tiny, quiet and personable songbirds are popular lab subjects and pets throughout the world. In this species, it is the male who builds the nest.



The researchers wallpapered the enclosures of 21 male zebra finches in one of three pastel colours; blue, pink or yellow. They then provided the birds with two colours of paper strips to build their nests -- one that matched and the other that mismatched the wallpaper -- and recorded the birds’ choices on video.

The finches mostly chose to build their nests with paper strips that matched the wallpaper (below left):

Zebra finch nests camouflaged with paper strips that matched the wallpaper of their enclosure (left), although most birds used a few mismatched paper strips to provide disruptive camouflage (right). Photograph: doi:10.1642/auk-14-77.1/University of St. Andrews.

The researchers concluded that camouflaged nests result from the birds’ intentional choices from amongst available nest materials -- the birds specifically selected materials that reduced the conspicuousness of their nests.



“Like us they don’t choose just any coloured material to build their homes”, said biologist Ida Bailey, a Postdoctoral Research Assistant and first author on the paper, in a press release.

“[T]hey avoid colours that would clash with their surroundings.”

Interestingly, the team found that the birds also included a small amount of colour-mismatched materials in their nest. These mismatched colours provide “disruptive camouflage”, which further helps muddle the visual outline of a nest (above image, right).

“We know from previous work that birds will learn to choose nest material of a colour they associate with a successful nesting attempt”, said Dr Bailey in a press release.

“Camouflage is, then, another feature of nest building that we now know birds consider when they choose the materials with which to build their nests.”

Dr Bailey added: camouflage may be “yet another aspect of nest building that inexperienced nest builders may get wrong and need to learn about during their lives.”

It’s interesting to note that research birds still camouflage their nests despite many hundreds of generations of captivity where they’ve not been exposed to predators -- how much stronger might this behaviour be in wild birds?

Sources:

Bailey I.E., Felicity Muth, Kate Morgan, Simone L. Meddle & Susan D. Healy (2015). Birds build camouflaged nests, The Auk, 132 (1) 11-15. doi:10.1642/auk-14-77.1 [OA]

University of St Andrews press release.

I wrote a version of this story as a featured two-minute podcast for BirdNote Radio. (Yes, this is my first ever radio podcast script!)

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Erratum [1842 on 15 January 2015]: This piece mistakenly omitted Felicity Muth as second author on this paper. The reference has been changed to correct this error.