Evidence for aggressive mimicry in an adult brood parasitic bird, and generalized defences in its host

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.

Hawk mimicry does not reduce attacks of cuckoos by highly aggressive hosts

“…Paired experiments with great reed warblers (Acrocephalus arundinaceus) by revealed that, when presented simultaneously with paired dummies (of common cuckoo, sparrowhawk Accipiter nisus, and turtle dove Streptopelia turtur), great reed warblers exhibit aggressive attack behaviors to both dummies, with higher attack intensities towards cuckoos and sparrowhawks. However, a study by Feeney et al (2015) suggested that tawny-flanked prinia (Prinia subflava) hosts were equally aggressive towards female cuckoo finches (Anomalospiza imberbis) and southern red bishops (Euplectes orix), suggesting successful mimicry of female bishops by female cuckoo finches.…”

When is resemblance mimicry?

“…At the broadest level, mimics may exhibit a divergent phenotype to their closest non‐mimetic relatives due to receiver‐mediated divergent selection (Figure a). This can be expected when the model is distantly related to the mimic, resulting in a relatively distinct mimetic phenotype (Feeney et al, ; de Jager et al, ; Johnson et al, ; Llaurens et al, ).…”

Fast and furious: host aggression modulates behaviour of brood parasites

“…During the evolutionary arms race between brood parasites and their hosts a lot of intriguing adaptations and counteradaptations have evolved. The most notable examples are egg mimicry of the common cuckoo ( Cuculus canorus , Brooke and Davies 1988) or the cuckoo finch ( Anamalospiza imberbis , Spottiswoode and Stevens 2011), egg rejection behaviour of their hosts (Wyllie 1981, Feeney et al 2015), destroying of host eggs by cowbirds ( Molothrus spp., Hoy and Ottow 1964) or killing of nestmates by nestlings of honeyguides (Indicatoridae, Spottiswoode and Koorevaar 2012).…”

“…It has been suggested that rapid egg-laying has evolved to avoid being spotted by hosts that could use this information when defending against parasitism. Indeed, it was found that several host species react to the presence of stuffed or model brood parasite by increasing the rejection rate of model parasitic eggs (Davies and Brooke 1988, Moksnes et al 1993, Bártol et al 2012, Feeney et al 2015, Samaš et al 2016). Brood parasites could also minimize the time they spent at host nests to simply avoid or at least minimize the impact of host aggression as the less time they spend at the host nest the fewer attacks they suffer.…”

“…We predicted that cuckoos should shorten the time they spent at host nests when they are spotted or under host attack. We also expected that cuckoos should always leave the host nest immediately after laying to minimize the chance that hosts spot them because hosts may use this information as a cue for subsequent egg rejection (Davies and Brooke 1988, Moksnes et al 1993, Bártol et al 2012, Feeney et al 2015, Samaš et al 2016). Moreover, despite the direct benefits of fast brood parasitism, many parasite species hinder themselves with additional activities that apparently prolong the whole event; cowbirds peck and break host eggs to reduce the clutch size in host nest (Astié and Reboreda 2006) and cuckoos, including the common cuckoo, frequently remove one or more hosts eggs which they subsequently eat (Wyllie 1981).…”