Mangrove GerygonesGerygone laevigastereject Little Bronze‐cuckooChalcites minutillushatchlings from parasitized nests

Visual mimicry of host nestlings by cuckoos

“…However, it is unclear whether this similarity has evolved through coevolution in response to discrimination by hosts, or to exploit the preexisting parent-offspring communication systems in order to facilitate competition with host young for food [14,45 -47]. By contrast, coevolution between Chalcites cuckoos and their hosts almost certainly has selected for mimicry of host nestlings by cuckoos because experimental studies show that (i) hosts of Chalcites cuckoos can reject parasite nestlings [11,18,19]; (ii) chick rejection is a specific response to brood-parasitism, such that hosts show flexibility in their responses to nestlings depending on the risk of parasitism [29]; and (iii) non-mimetic nestlings suffer a survival cost [11]. Thus, our results provide novel evidence of a further escalation in the coevolutionary arms race between cuckoos and their hosts: the evolution of visual mimicry of host nestlings by cuckoos in response to rejection by hosts.…”

Grey Gerygone hosts are not egg rejecters, but Shining Bronze-Cuckoos lay cryptic eggs

“…This dilution effect would become even more valuable if hosts discriminate against cuckoo chicks after hatching (Sato et al 2010a), and chick rejection may be more likely to evolve if hosts show weak defenses at earlier stages (Langmore et al 2003, Grim 2006, Yang et al 2015. Other Gerygone species reject Chalcites cuckoo chicks but not eggs (Sato et al 2010b, 2015, Tokue and Ueda 2010, so perhaps Grey Gerygones might also show chick discrimination (Gill 1998, Grim 2011). This deserves further study.…”

Host–parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird

“…Furthermore, during the late nestling and fledgling periods, baywings often have helpers at the nest that contribute to young provisioning and may reduce the costs to host parents of raising parasitized broods to independence [47,48]. In theory, hosts may evolve defences against parasitic young either when parasites have broken down earlier lines of defence [15] or when they are constrained from evolving defences against parasite eggs [17]. In baywings, the evolution of fledgling discrimination in the absence of rejection behaviour against parasite eggs and nestlings suggests that they might be prevented from reliably discriminating against parasitic eggs or chicks [25].…”

“…and Chrysococcyx minutillus) and their hosts have shown that host parents were able to reject parasitic chicks either through the desertion of parasitized nests soon after hatching [15] or active eviction of parasitic young out of the nest [16,17], and later work suggests that host rejection behaviour, in turn, may have selected for reciprocal host chick mimicry in bronzecuckoos [15,18]. These findings have challenged prior theoretical arguments that learned chick discrimination would be maladaptive in hosts of evictor brood parasites such as cuckoos [19] (see also [20]) and suggest that a coevolutionary arms race similar to that observed at the egg stage may also occur at the nestling stage [15][16][17] (but see [21]). Visual mimicry of host chicks has also been reported in parasitic finches (Vidua sp.…”