In a neat experiment on bird interior design, researchers show that finches conceal their nests by deliberately choosing construction materials that blend in with the background of the nest site. The work, published in The Auk last week, is the first study to provide experimental evidence that birds actively select camouflaging materials.
Previous work have shown that birds will move their nest to reduce predation risk, and researchers have long assumed that birds also conceal their nests using camouflage to cut down on egg and nestling loss to predators. However, no experimental studies have tested this.
So, a U.K. team led by Ida Bailey from the University of St. Andrews offered 21 male zebra finches (Taeniopygia guttata) a choice of nest-building materials that either matched or didn’t match the color of their nest cup and the surrounding cage walls. The cages were wallpapered in different nursery-room pastels -- blue, pink, or yellow, New Scientist reports -- and the birds had to choose between strips of paper in two different colors. The team filmed the birds’ selections.
Males largely chose nesting material that matched the background color of the cage (pictured to the right), confirming that camouflaged nests in the wild aren’t simply a lucky result of available materials. And this skill in making a nest less conspicuous isn’t innate; rather, it’s an experience-dependent process where the birds have to learn what works best.
“Like us they don’t choose just any colored material to build their homes, they avoid colors 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,” Bailey explains in a news release. “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.”
Furthermore, many of the finches chose a small proportion of paper strips that were not the same color as the cage walls. This suggests that finches also employ an additional method of roost disguise known as disruptive camouflage: A small proportion of non-camouflage, contrasting material woven in breaks up the nest’s outline, making it appear less like a nest.