Nest decoration: birds exploit a fear of feathers to guard their nest from usurpation.

Tore Slagsvold,Karen L. Wiebe

doi:10.1098/rsos.211579

Tore Slagsvold, Karen L. Wiebe

Open Access

https://doi.org/10.1098/rsos.211579

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Abstract

Many species of birds incorporate feathers into their nest as structural support and to insulate the eggs or offspring. Here, we investigated the novel idea that birds reduce the risk of nest usurpation by decorating it with feathers to trigger a fear response in their rivals. We let prospecting birds choose between a dyad of nest-boxes in the wild, both containing some nest materials, but where one had a few white feathers and the other had none. All three species of cavity-nesting birds studied, the pied flycatcher Ficedula hypoleuca, the blue tit Cyanistes caeruleus, and the tree swallow Tachycineta bicolor, hesitated to enter boxes with white feathers. A similar avoidance of white feathers was found when the alternative nest-box of a dyad held black feathers. However, the birds readily collected white feathers that we placed in front of their nest-box, showing the fear of such feathers was context-dependent. We suggest that naive prospecting birds may perceive feathers in nests as the result of a predation event, and that owners decorate nests with bright feathers that can be seen from the opening to deter others from entering.

Highlights

Breeding birds may suffer heavily from predation, selecting for a number of behaviours to avoid the risk [1,2], including choice of habitat and nest site [3,4] and behaviour at the nest [5,6]
We used commercial feathers to standardize their colour and form between trials. We offered these commercial feathers on the ground near blue tit nests to see whether the birds avoided them in general or only when seen inside a dark cavity
Why birds decorate their nest with feathers

Summary

Introduction

Breeding birds may suffer heavily from predation, selecting for a number of behaviours to avoid the risk [1,2], including choice of habitat and nest site [3,4] and behaviour at the nest [5,6]. There may be strong competition for the safest sites among secondary cavity-nesting birds which try to escape predation by avoiding cavities with large entrances where the risk of nest predation is greater [7,8]. Competition for cavities may force birds to investigate unfamiliar, dark holes which may be dangerous to enter because an attacking animal may be hiding inside, such as stinging insects, poisonous herptiles, rodents, mustelids or raptors. Like small owls, may use cavities for plucking and eating avian prey [9], often leaving prey remains, faeces, urine and scents.

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