Birds Decorating Their Nests With Plastic May Suffer Less Egg Depredation by Corvids

ABSTRACT Many birds add anthropogenic material to the nest. This may increase the probability of total failure because the nest may be more easily located by enemies. However, the material may also induce a threat response in predators sceptical to new objects (the Neophobia Hypothesis). We presented artificial nests on the ground each with two quail eggs, in territories of Eurasian magpies Pica pica in spring. Some nests were decorated with pieces of white plastic while others were not (control). When nests of both types were presented simultaneously on a magpie territory and only a meter apart, depredation started later for nests with plastic than for control nests, supporting the Neophobia Hypothesis. When a trial was repeated on the same territory later in the season, predation started sooner. However, this was probably caused by habituation to the experimental set up (wildlife camera and artificial nests) and not to the plastic itself because in the repeated trials, the eggs in the nests with plastic were still depredated later than the eggs in the control nests. The nests were not depredated sooner if similar experiments had been conducted on the same territory in the previous year. The onset of depredation was no sooner in territories that initially contained plastic close to the magpie nest than in territories containing no plastic. Finally, when only a single nest was presented on a magpie territory, the time lag until depredation was similar for decorated and control nests, suggesting that the increased detectability caused by decoration outweighed the fear response to the plastic. We conclude that the Neophobia Hypothesis may be relevant to natural cases including birds nesting in habitats containing anthropogenic material and to circumstances with repeated visits by corvids to bird nests, such as in a bird colony.