Armed Rollers: Does Nestling’s Vomit Function as a Defence against Predators?

Deseada Parejo,Lourdes Sánchez,Carmen Zamora-Muñoz,Jesús M Avilés,Francisca Ruano,Aránzazu Peña,Manuel Martín-Vivaldi

doi:10.1371/journal.pone.0068862

Abstract

Chemical defences against predators are widespread in the animal kingdom although have been seldom reported in birds. Here, we investigate the possibility that the orange liquid that nestlings of an insectivorous bird, the Eurasian roller (Coracias garrulus), expel when scared at their nests acts as a chemical defence against predators. We studied the diet of nestling rollers and vomit origin, its chemical composition and deterrent effect on a mammal generalist predator. We also hypothesized that nestling rollers, as their main prey (i.e. grasshoppers) do from plants, could sequester chemicals from their prey for their use. Grasshoppers, that also regurgitate when facing to a threat, store the harmful substances used by plants to defend themselves against herbivores. We found that nestling rollers only vomit after being grasped and moved. The production of vomit depended on food consumption and the vomit contained two deterrent chemicals (hydroxycinnamic and hydroxybenzoic acids) stored by grasshoppers and used by plants to diminish herbivory, suggesting that they originate from the rollers’ prey. Finally, we showed for the first time that the oral secretion of a vertebrate had a deterrent effect on a model predator because vomit of nestling rollers made meat distasteful to dogs. These results support the idea that the vomit of nestling rollers is a chemical defence against predators.

Highlights

Chemical defence is one of the mechanisms that organisms use to enhance their survival prospects
In this paper we first show that arthropods from the order Orthoptera are the main prey of roller nestlings in the study area
We demonstrate that the vomit expelled by roller nestlings depends on food provided by parents and that vomiting is triggered by grasping and moving of nestlings

Summary

Introduction

Chemical defence is one of the mechanisms that organisms use to enhance their survival prospects. Birds have not been included in lists of chemically-defended animals until the end of the twentieth century [5], when species of the genus Pitohui were found to deter predators and/or parasites by means of the neurotoxin homobatrachotoxin that is contained in their tissues [7]. Apart from this extreme example of poisonous Pitohuis, several other bird species contain toxic or unpalatable compounds that may help to defend them (see reviews in [5,8]). Hoopoes Upupa epops and green woodhoopoes Phoeniculus purpureus, when disturbed at the holes where they roost, secrete drops of a fetid substance from their uropygial glands [9]

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