Egg Eviction Imposes a Recoverable Cost of Virulence in Chicks of a Brood Parasite

Andrew Iwaniuk,Michael G. Anderson,Mark E. Hauber,Tomáš Grim,Miklós Bán,Phillip Cassey,Csaba Moskát

doi:10.1371/journal.pone.0007725

Abstract

BackgroundChicks of virulent brood parasitic birds eliminate their nestmates and avoid costly competition for foster parental care. Yet, efforts to evict nest contents by the blind and naked common cuckoo Cuculus canorus hatchling are counterintuitive as both adult parasites and large older cuckoo chicks appear to be better suited to tossing the eggs and young of the foster parents.Methodology/Principal FindingsHere we show experimentally that egg tossing imposed a recoverable growth cost of mass gain in common cuckoo chicks during the nestling period in nests of great reed warbler Acrocephalus arundinaceus hosts. Growth rates of skeletal traits and morphological variables involved in the solicitation of foster parental care remained similar between evictor and non-evictor chicks throughout development. We also detected no increase in predation rates for evicting nests, suggesting that egg tossing behavior by common cuckoo hatchlings does not increase the conspicuousness of nests.ConclusionThe temporary growth cost of egg eviction by common cuckoo hatchlings is the result of constraints imposed by rejecter host adults and competitive nestmates on the timing and mechanism of parasite virulence.

Highlights

The remarkable ability of the common cuckoo hatchlings Cuculus canorus to evict host eggs and nestmates from the nest (Fig. 1) has fascinated naturalists since the time of Aristotle [1,2] but was first documented in the scientific literature much later – about 220 years ago [3]
The temporary growth cost of egg eviction by common cuckoo hatchlings is the result of constraints imposed by rejecter host adults and competitive nestmates on the timing and mechanism of parasite virulence
We studied cuckoos that hatched in the deep nests of a relatively large host [18,19], the great reed warbler Acrocephalus arundinaceus, and measured differences in growth rates between hatchlings that evicted natural nest contents and those whose nests were experimentally emptied

Summary

Introduction

The remarkable ability of the common cuckoo hatchlings Cuculus canorus (hereafter: cuckoo) to evict host eggs and nestmates from the nest (Fig. 1) has fascinated naturalists since the time of Aristotle [1,2] but was first documented in the scientific literature much later – about 220 years ago [3]. Eviction represents a virulent behavioral strategy to eliminate costly competition with nestmates [4,5,6] Both the mother parasites, that remove one or more host eggs when laying her own egg [7], and older cuckoo nestlings, that are larger and beg more intensely than host chicks [8], appear to be better equipped to eliminate eggs or cohabiting nestmates. Cuckoo nestlings in nests of clutch size adjuster hosts will not receive increased parental provisioning with increased begging intensity, and might even be less likely to survive to fledge. Efforts to evict nest contents by the blind and naked common cuckoo Cuculus canorus hatchling are counterintuitive as both adult parasites and large older cuckoo chicks appear to be better suited to tossing the eggs and young of the foster parents

Methods

Results

Conclusion