Abstract

Mimicry of a harmless model (aggressive mimicry) is used by egg, chick and fledgling brood parasites that resemble the host's own eggs, chicks and fledglings. However, aggressive mimicry may also evolve in adult brood parasites, to avoid attack from hosts and/or manipulate their perception of parasitism risk. We tested the hypothesis that female cuckoo finches (Anomalospiza imberbis) are aggressive mimics of female Euplectes weavers, such as the harmless, abundant and sympatric southern red bishop (Euplectes orix). We show that female cuckoo finch plumage colour and pattern more closely resembled those of Euplectes weavers (putative models) than Vidua finches (closest relatives); that their tawny-flanked prinia (Prinia subflava) hosts were equally aggressive towards female cuckoo finches and southern red bishops, and more aggressive to both than to their male counterparts; and that prinias were equally likely to reject an egg after seeing a female cuckoo finch or bishop, and more likely to do so than after seeing a male bishop near their nest. This is, to our knowledge, the first quantitative evidence for aggressive mimicry in an adult bird, and suggests that host–parasite coevolution can select for aggressive mimicry by avian brood parasites, and counter-defences by hosts, at all stages of the reproductive cycle.

Highlights

  • Avian brood parasites lay their eggs in the nests of other birds, foisting the cost of parental care onto the host

  • Female cuckoo finches look more similar in colour to female Euplectes weavers than either to conspecific males or to females of their closest relatives; more similar in pattern to Euplectes weavers than to females of their closest relatives; and plumage luminance did not significantly differ across taxa. These data suggest that female cuckoo finch plumage colour and pattern are not an artefact of common ancestry or convergent evolution resulting from shared ecological pressures, but are consistent with a hypothesis of brood parasite–host coevolution

  • Our data suggest that female cuckoo finches are aggressive mimics of female Euplectes weavers and that their prinia rspb.royalsocietypublishing.org Proc

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Summary

Introduction

Avian brood parasites lay their eggs in the nests of other birds, foisting the cost of parental care onto the host. Using model presentation experiments at prinia nests, we investigated whether host parents distinguished female and male cuckoo finches (i.e. putative mimic and dissimilar-looking male) from female and male southern red bishops (Euplectes orix, a common Euplectes weaver at our study site, hereafter ‘bishop’; i.e. putative model and dissimilar-looking control). After finding that prinias were aggressive towards female cuckoo finches and female bishops, but not towards their male counterparts near their nests (see Results), we conducted coupled model presentation and egg rejection experiments to test whether prinias exhibited brood parasitespecific defences towards both female cuckoo finches and female bishops. We used linear mixed-effects models to test whether female cuckoo finch plumage (colour, luminance and pattern) was more similar to that of sympatric female Euplectes weaver or Vidua finch species. Full and final model outputs are presented in the electronic supplementary material, tables S2–S7

Results
Findings
Discussion

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