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

TL;DR

Birds that decorate nests with plastic may be less likely to have their eggs stolen by magpies due to the magpies' fear of new objects.

Contribution

The study provides empirical evidence supporting the Neophobia Hypothesis in the context of nest predation by corvids.

Findings

Nests decorated with plastic were depredated later than control nests when presented simultaneously.

Repeated exposure to the experimental setup caused habituation, but plastic-decorated nests were still depredated later.

The increased detectability of plastic-decorated nests outweighed the fear response when only one nest was presented.

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.

Many birds add anthropogenic material to the nest. We presented artificial nests on the ground in spring, each with two quail eggs and half of them decorated with pieces of white plastic. The plastic induced a neophobic response in territorial European magpies, reducing the rate of nest predation.

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