Search

Background: Avian brood parasites and their hosts are involved in complex offence-defense coevolutionary arms races. The most common pair of reciprocal adaptations in these systems is egg discrimination by hosts and egg mimicry by parasites. As mimicry improves, more advanced host adaptations evolve such as decreased intra- and increased interclutch variation in egg appearance to facilitate detection of parasitic eggs. As interclutch variation increases, parasites able to choose hosts matching best their own egg phenotype should be selected, but this requires that parasites know their own egg phenotype and select host nests correspondingly. Methodology/Principal Findings: We compared egg mimicry of common cuckoo Cuculus canorus eggs in naturally parasitized marsh warbler Acrocephalus palustris nests and their nearest unparasitized conspecific neighbors having similar laying dates and nest-site characteristics. Modeling of avian vision and image analyses revealed no evidence that cuckoos parasitize nests where their eggs better match the host eggs. Cuckoo eggs were as good mimics, in terms of background and spot color, background luminance, spotting pattern and egg size, of host eggs in the nests actually exploited as those in the neighboring unparasitized nests. Conclusions/Significance: We reviewed the evidence for brood parasites selecting better-matching host egg phenotypes from several relevant studies and argue that such selection probably cannot exist in host-parasite systems where host interclutch variation is continuous and overall low or moderate. To date there is also no evidence that parasites prefer certain egg phenotypes in systems where it should be most advantageous, i.e., when both hosts and parasites lay polymorphic eggs. Hence, the existence of an ability to select host nests to maximize mimicry by brood parasites appears unlikely, but this possibility should be further explored in cuckoo-host systems where the host has evolved discrete egg phenotypes. [ABSTRACT FROM AUTHOR]

We documented brood parasitism by the poorly studied Large Hawk-Cuckoo on a previously unknown host species, the Chinese Babax. Furthermore, we describe a new egg colour for the Large Hawk-Cuckoo. The parasitism rate of Chinese Babax nests over 4 years was 6.9% (11 of 159 nests), with significant temporal variation. The Large Hawk-Cuckoo laid immaculate white eggs that appeared non-mimetic to the blue Babax eggs, an impression that was confirmed by avian visual modelling. Nevertheless, most Cuckoo eggs were accepted by the host, suggesting that this host-parasite system may be evolutionarily recent. [ABSTRACT FROM AUTHOR]

Brood-parasitic birds such as cuckoos and cowbirds lay eggs with unusual by strong shells. Three main hypotheses have been proposed to explain the adaptive significance of this trait. The present study focused on the puncture resistance hypothesis and tested its critical prediction that increased eggshell strength enhances the probability that the parasitic egg is accepted by the host. To address the problem, we experimentally parasitized marsh warbler, Acrocephalus palustris, nests with three types of real eggs having similar size but differing in eggshell strength and/or mimicry: (1) great reed warbler, Acrocephalus arundinaceus, eggs painted to be nonmimetic; (2) common cuckoo, Cuculus canorus, eggs painted in the same way; and (3) unmanipulated cuckoo eggs. When we controlled for mimicry, ejection of strong-shelled (cuckoo) eggs was considerably more costly than ejection of weak-shelled (great reed warbler) eggs. However, nonmimetic cuckoo eggs were not more likely to be accepted than nonmimetic great reed warbler eggs, suggesting no effect of eggshell strength alone on rejection decisions. Mimetic cuckoo eggs were accepted more often than the eggs painted to be nonmimetic suggesting that mimicry primarily determines the probability of rejection. Thus, we found no support for the puncture resistance hypothesis in marsh warblers, which is a host with well-developed defence mechanisms against cuckoo parasitism. [Copyright &y& Elsevier]

Using multiple logistic regression analysis, we investigated the influence of nest site characteristics, laying date and nest size in marsh warblers Acrocephalus palustris on the risk of parasitism by common cuckoos Cuculus canorus. Marsh warblers breed in more diverse and dense herbaceous vegetation than other cuckoo hosts investigated in comparable studies. The “perch proximity” hypothesis was supported as parasitized nests were situated closer to trees than non-parasitized ones. Furthermore, demonstrated for the first time in a cuckoo host, tree height was an important predictor of parasitism, with higher trees increasing the parasitism odds ratio. The “nest exposure” hypothesis was also supported since parasitized nests had a shorter stand of vegetation in the close vicinity than non-parasitized nests. However, visibility of the nest from the nearest potential cuckoo perch (cuckoo view) was not selected by the model, probably because most nests were well concealed. Laying date, height of nest above ground and the distance from the nest to the nearest edge of the vegetation were not important predictors of parasitism. Though smaller nests tended to be parasitized more frequently than larger ones, nest size only approached significance, making its importance unclear. [ABSTRACT FROM AUTHOR]

Although Old World buntings (Emberizinae) may be considered suitable Common Cuckoo (Cuculus canorus) hosts, there is at present no evidence that any of the European species are regularly parasitized. Most historical parasitism records refer to the Yellowhammer (Emberiza citrinella) and Reed Bunting (E. schoeniclus). Both of these species reject almost 100% of experimentally added nonmimetic eggs, and also a considerable proportion of experimentally added conspecific eggs, showing exquisite egg discrimination abilities. In this paper, we report Common Cuckoo parasitism and egg rejection behavior in a Bulgarian population of another Old World Emberizinae, the Corn Bunting (Miliaria calandra). We found this species was regularly parasitized (9%, 8 of 90 nests) and that the parasitism rate was consistent among the three years of our study. Naturally laid Common Cuckoo eggs were fairly good mimics of host eggs and most were accepted (5 of 7). The Corn Bunting proved to be a suitable Common Cuckoo host as we recorded a successfully fledged cuckoo chick. Unlike Yellowhammers and Reed Buntings, Corn Buntings rejected only 42% (16 of 38) of experimentally introduced nonmimetic model Common Cuckoo eggs and none of the experimentally introduced conspecific eggs (n = 13). Parasitized nests had more and higher trees in the vicinity than unparasitized nests and breeding habitat characteristics may explain the difference in egg discrimination abilities between Corn Buntings and other Old World Emberizinae. [ABSTRACT FROM AUTHOR]

The article presents a study which examines egg discrimination following failed rejection attempts in a small cuckoo host. Conducted in northwestern Bulgaria, the study examined egg rejection behaviour in a host of common cuckoo Cuculus canorus and the eastern olivaceous warbler Hippolais pallida. Key findings indicate that olivaceous warblers failed to hold cuckoo eggs and can only remove them selectively by puncture ejection. Since the real cuckoo eggs were rejected at a very same rate suggests no appreciable discrimination in inferences from artificial eggs.