Color plumage polymorphism and predator mimicry in brood parasites

Abstract

BackgroundPlumage polymorphism may evolve during coevolution between brood parasites and their hosts if rare morph(s), by contravening host search image, evade host recognition systems better than common variant(s). Females of the parasitic common cuckoo (Cuculus canorus) are a classic example of discrete color polymorphism: gray females supposedly mimic the sparrowhawk (Accipiter nisus), while rufous females are believed to mimic the kestrel (Falco tinnunculus). Despite many studies on host responses to adult cuckoos comprehensive tests of the “hawk mimicry” and “kestrel mimicry” hypotheses are lacking so far.ResultsWe tested these hypotheses by examining host responses to stuffed dummies of the sparrowhawk, kestrel, cuckoo and the innocuous turtle dove (Streptopelia turtur) as a control at the nest. Our experimental data from an aggressive cuckoo host, the great reed warbler (Acrocephalus arundinaceus), showed low effectiveness of cuckoo-predator mimicry against more aggressive hosts regardless of the type of model and the degree of perfection of the mimic. Specifically, warblers discriminated gray cuckoos from sparrowhawks but did not discriminate rufous cuckoos from kestrels. However, both gray and rufous cuckoos were attacked vigorously and much more than control doves. The ratio of aggression to gray vs. rufous cuckoo was very similar to the ratio between frequencies of gray vs. rufous cuckoo morphs in our study population.ConclusionsOverall, our data combined with previous results from other localities suggest polymorphism dynamics are not strongly affected by local predator model frequencies. Instead, hosts responses and discrimination abilities are proportional, other things being equal, to the frequency with which hosts encounter various cuckoo morphs near their nests. This suggests that female cuckoo polymorphism is a counter-adaptation to thwart a specific host adaptation, namely an ability to not be fooled by predator mimicry. We hypothesize the dangerousness of a particular model predator (sparrowhawks are more dangerous to adult birds than kestrels) may be another important factor responsible for better discrimination between the gray cuckoo and its model rather than between the rufous cuckoo and its model. We also provide a review of relevant existing literature, detailed discussion of plumage polymorphism in cuckoos, methodological recommendations and new ideas for future work.

Repeatability of Host Female and Male Aggression Towards a Brood Parasite

“…Moreover, given that common cuckoo females are dimorphic in colour plumage and may imitate some raptors (sparrowhawks and kestrels, Voipio ; Honza et al. ; Davies & Welbergen ; Trnka & Grim ), consistently aggressive behaviour against common cuckoos may also be a strategy to minimize parasitism risk (see also Thorogood & Davies ; Trnka & Prokop ). Although it seems maladaptive for individuals to not respond strategically with respect to the local parasitism pressure (Welbergen & Davies ), consistent host behaviour may be preferred when the local risk of parasitism is high and does not fluctuate over longer periods of time.…”

Alarm call‐based discrimination between common cuckoo and Eurasian sparrowhawk in a Chinese population of great tits

“…The ability of hosts to distinguish parasites was often tested by comparing observed behavioral reactions when they faced alive cuckoos and hawks or specimens (Trnka & Grim, ; Trnka & Prokop, ; Trnka et al., ; Welbergen & Davies, , ). However, birds usually produce alarm calls in addition to showing behavioral responses when in danger (Caro, ).…”

Do rufous common cuckoo females indeed mimic a predator? An experimental test

“…Classic examples include brood parasitic cuckoos. The disproportionally high frequency of plumage polymorphism in parasitic cuckoos was noted a half‐century ago (Voipio, ; Payne, ), but experimental study of colour variation in this group is still in its infancy (for reviews see Thorogood & Davies, ; Trnka & Grim, ).…”