Why do birds construct nest tails? A test of disruptive camouflage in the blue manakin

Nests are extended phenotypes capable of providing brood protection against predators, and because they are motionless structures, camouflage is expected to emerge. Birds from different families construct a tail of hung materials underneath their nests, which has been hypothesized to be a type of disruptive camouflage, i.e. an appendage that gives a nest a false shape for hindering detection by predators. Predictions of this hypothesis are that for predators that are visually oriented, nests without a tail are easier to detect, yet this hypothesis never received support likely because predator species and other variables were not considered. Here, we compared predation between nests of blue manakins for which tails were maintained or experimentally removed. To avoid the effects of parental movements in predator's attraction, we used real inactive nests with Plasticine eggs. We also controlled for nest site variables and excluded nests depredated by olfactory animals by monitoring nests with infrared camera traps. Predation was 10 times higher in nests without a tail, and tail absence was the only significant variable explaining nest predation. Furthermore, all of the recorded predators were visually oriented. This is the first work confirming the antipredatory adaptive function of avian nest tails, and corroborated the disruptive camouflage hypothesis.