When Choosing Nest Materials, Birds are Sneaky Decorators

Birds, it seems, are pretty anal home-builders, often only choosing nest materials that best match their surroundings. However, this isn't simple decor preference. Researchers are now suggesting that this shows a natural instinct to camouflage their home.

That's at least according to a study recently published in the journal Bio One, which details how zebra finches have a notable penchant for matching colors when making a nest.

To determine this, an international collaboration of researchers from the University of St Andrews, the University of Arizona, and the University of Edinburgh presented male zebra finches (Taeniopygia guttata) with two choices of colored paper (either blue or pink) to build their nests with. The walls of these birds' cages were also lined with either blue or pink wallpaper to serve as their environmental background.

Without fail, the males always exclusively chose material matching the color of the walls - as long as there was enough of it.

The researchers suggest that this indicates that birds will actively choose to build their nests in a way that causes them to blend in with their surroundings, as opposed to the assumption that most nests are camouflaged because the available materials (fallen twigs, bark, etc.) simply made it that way.

According to investigator Ida Bailey, from St Andrews' School of Biology, past research conducted by the university had indicated that nest building is often a learning experience for birds, during which they increasingly will choose better materials as the years go by.

"We know from previous work that birds will learn to choose nest material of a color they associate with a successful nesting attempt but this is the first evidence that they choose material so as to camouflage their nests," she said in a statement. "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."

Intriguingly, when a third color (green) was introduced into the choices, the finches were found to include one or two strips in the overall nest. Perhaps this was to give the nests a little character, but Bailey and her colleagues have another theory.

According to the study, this best reflects a camouflage strategy called "disruptive camouflage." In nature, not everything is uniform. In that case, incorporating a little bit of uncharacteristic material helps break an otherwise uniform patch in a predator's field of vision, helping conceal a nest's form even more.

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