Plastering mud around the entrance hole affects the estimation of threat levels from nest predators in Eurasian Nuthatches

Jiangping Yu,Jian Fang,Haitao Wang,Guodong Yi,Li Zhang,Jiyuan Yao,Chao Shen,Keqin Zhang

doi:10.1186/s40657-021-00294-1

Abstract

BackgroundFor cavity-nesting birds, the nest entrance plays an important role in preventing predators from accessing nests. Several species of nuthatches use mud to narrow the entrance of cavities. In theory, the smaller the entrance hole size, the more effective it is against predators; however, few studies have tested whether narrowing the entrance hole size can affect the estimation of threat levels from nest predators in cavity-nesting birds.MethodsUsing dummy experiments, we tested whether Eurasian Nuthatches (Sitta europaea, narrow the entrance hole of cavities) and Cinereous Tits (Parus cinereus, do not narrow the entrance hole, as a control) perform different nest defence behaviours against Common Chipmunks (Tamias sibiricus, small nest predator) and Red Squirrels (Sciurus vulgaris, larger nest predator).ResultsBoth nuthatches and tits exhibited stronger response behaviours (high dummy response scores) against chipmunks than against squirrels. Compared with tits, nuthatches exhibited more aggressive behaviours to chipmunks, but their responses to squirrels were similar.ConclusionsNest defence behaviours of nuthatches to chipmunks differed from tits, and the results suggested that nuthatches might estimate threat levels of nest predators according to their narrowed entrance-hole size.

Highlights

For cavity-nesting birds, the nest entrance plays an important role in preventing predators from accessing nests
The body size of a predator is a reliable indicator of the threat level that it poses to birds (Swaisgood et al 1999), and it is especially important in some predators that they are quite similar in overall appearance as well as body shape (Beránková et al 2014)
Nuthatches and tits exhibited different nest defence behaviours against the same nest predators, and the results showed that those two species implemented different nest defence strategies

Summary

Introduction

For cavity-nesting birds, the nest entrance plays an important role in preventing predators from accessing nests. Nest predation is the most important factor impeding successful breeding in birds (Ricklefs 1969; Martin 1995; Caro 2005; Lima 2009) Under such selection pressure, birds have evolved complex anti-predation strategies to protect their nests and perform specific nest defence behaviours when facing different types or. It has been shown that various bird species can distinguish between raptors differing in size and perform appropriate antipredator response behaviours (Evans et al 1993; Templeton et al 2005; Courter and Ritchison 2010) Many factors, such as habitat, nest stage, sex, nest type and predator location, may influence and cause changes in nest defence behaviour of birds (Burger 1992; Ritchison 1993; Møller et al 2016; Crisologo and Bonter 2017). Alarm calling rates increased with the nesting stage in Southern House Wrens (Troglodytes musculus) (Fasanella and Fernández 2009)

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