Differences in morphology and colour pattern of shiny cowbird (Molothrus bonariensis) eggs found in nests of two hosts

M Alicia De La Colina,Bettina Mahler,Juan Carlos Reboreda

doi:10.1111/j.1095-8312.2011.01605.x

M Alicia De La Colina, Bettina Mahler + Show 1 more

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https://doi.org/10.1111/j.1095-8312.2011.01605.x

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Abstract

Genetic differentiation among shiny cowbird (Molothrus bonariensis) females that use different hosts indicates that in this brood parasite, host use is not random at an individual level. We tested whether there exist differences in morphology and coloration between eggs of shiny cowbirds laid in the nests of two different hosts, the chalk-browed mockingbird (Mimus saturninus) and the house wren (Troglodytes aedon). We took morphometric measures of shiny cowbird eggs found in nests of mockingbirds and wrens and analysed their coloration using digital photography and reflectance spectrometry. We found that shiny cowbird eggs found in mockingbird nests were wider and more asymmetric than those found in wren nests. In addition, cowbird eggs coming from mockingbird nests were brighter and had higher relative red reflectance than those coming from wren nests. Our results show that shiny cowbird eggs laid in nests of two different hosts vary in shape and background colour, but not in spotting pattern.

Highlights

Avian obligate brood parasites are completely dependent on other species, the hosts, to raise their offspring
In the common cuckoo Cuculus canorus, a host-generalist brood parasite, this co-evolutionary process has led to female lineages becoming host specialists and evolving mimetic eggs that resemble those of particular hosts (Brooke & Davies, 1988; Moksnes & Røskaft, 1995; Gibbs et al, 2000; Avilés, 2008; Stoddard & Stevens, 2010)
The shiny cowbird (Molothrus bonariensis), a highly generalist brood parasite that uses more than 240 species as hosts (Friedmann & Kiff, 1985; Ortega, 1998; Lowther & Post, 1999), shows eggs with extreme variation in their colour pattern, in background colour, and in spotting density (Fig. 1)

Summary

Introduction

Avian obligate brood parasites are completely dependent on other species, the hosts, to raise their offspring. In the common cuckoo Cuculus canorus, a host-generalist brood parasite, this co-evolutionary process has led to female lineages becoming host specialists and evolving mimetic eggs that resemble those of particular hosts (Brooke & Davies, 1988; Moksnes & Røskaft, 1995; Gibbs et al, 2000; Avilés, 2008; Stoddard & Stevens, 2010). Most brood parasitic cowbirds (Molothrus spp.) have eggs of polymorphic coloration (Ortega, 1998). The shiny cowbird (Molothrus bonariensis), a highly generalist brood parasite that uses more than 240 species as hosts (Friedmann & Kiff, 1985; Ortega, 1998; Lowther & Post, 1999), shows eggs with extreme variation in their colour pattern, in background colour, and in spotting density (Fig. 1).

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