Behaviour 2019
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Host egg signatures are an effective defence against near-perfect mimicry by cuckoos
Jess Lund1,2, Tanmay Dixit2, Silky Hamama3, Mairenn Attwood2, Gabriel Jamie1,2, Claire Spottiswoode1,2. 1FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Cape Town, Western Cape, South Africa; 2Department of Zoology, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom; 3Musumanene Farm, Choma, Southern Province, Zambia

Rejection of foreign eggs is a common defence against brood parasitism, but how can hosts maximise the likelihood of correctly identifying a cheat when mimicry is near-perfect at the population level? In brood parasite-host systems, as with most other mimicry systems, imperfect mimicry is the norm, and we lack studies of the rejection strategies of hosts in systems where mimicry is highly accurate. Here I show that mimicry of fork-tailed drongo Dicrurus adsimilis eggs by African cuckoos Cuculus gularis (a poorly studied Afrotropical brood parasite-host system) is near-perfect, but that a high degree of interclutch variation (egg ‘signatures’) means that drongos still have the upper hand in the arms race. I further explore the costs and benefits of drongos and cuckoos being in different clusters in phenotypic space, and discuss whether phenotypic clustering is an adaptive trait or a product of a mechanistic constraint.