Researchers at the University of St Andrews have produced the first experimental evidence that birds actively select nest-building materials that camouflage their nests: published today in influential ornithological journal The Auk.
Scientists from the University's School of Biology wallpapered male zebra finches' (Taeniopygia guttata) cages in different colours before filming them choose which colour of material with which to build their nests.
Given the choice of paper strips in two different colours, zebra finches largely chose strips that were a colour-match to the paper covering the walls of their cage.
These findings confirm that birds choose to camouflage their nests by matching the colour of material they use to the nests background, rather than happening to build camouflaged nests as a simple consequence of the materials that are available.
Being able to match the nest material to the nest site in this way may help the birds to conceal their nests from predators. Predation is a major cause of nest loss for birds. While there is good evidence that birds will move their nest in order to reduce predation risk, this is the first data to show that birds will camouflage their nests in order to reduce predation.
What's more, many of the zebra finches chose a small proportion of paper strips that were not the same colour as the cage walls, suggesting that birds may also employ a second method of disguise to conceal their nests known as disruptive camouflage. By using a small proportion of non-camouflage material in the nest the bird may break up the outline of its nest so that it look less like a nest and is, therefore, less attractive to predators.
The findings build on previous research carried out by the University of St Andrews, which showed that nest building is not just an innate skill but is an experience-dependent process during which birds learn what works best.
Report author, Dr Ida Bailey said:
"We know from previous work that birds will learn to choose nest material of a colour they associate with a successful nesting attempt but this is the first evidence that they choose material so as to camouflage their nests. 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.
"Like us they don't choose just any coloured material to build their homes, they avoid colours that would clash with their surroundings. Knowing this gives us a better idea of how birds may actively reduce the chances of predators finding their nests. It also opens up the possibility that this is yet another aspect of nest building that inexperienced nest builders may get wrong and need to learn about during their lives."
More information: "Birds build camouflaged nests." Ida E. Bailey, et al. The Auk 132(1):11-15. 2015 doi: dx.doi.org/10.1642/AUK-14-77.1
Provided by: University of St Andrews