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Birds are capable of seeing the ultraviolet light ( UV) spectrum and as a consequence have evolved UV-reflective structures with signalling functions. Avian eggs also reflect in the UV spectrum but the importance of UV egg matching in egg rejection decisions has been equivocal. Here we conducted egg rejection experiments in the congeneric and sympatrically breeding Yellow-bellied Prinia Prinia flaviventris and Plain Prinia Prinia inornata in Taiwan to assess the role of UV as a cue in egg discrimination. Yellow-bellied Prinia is a host of Oriental Cuckoo Cuculus optatus, whereas Plain Prinia is not. We coated one prinia egg in the experimental clutches with a cream containing a UV-blocking agent, while the rest of the eggs were coated with cream only. We also experimentally parasitized prinias with non-mimetic model eggs with reduced UV reflectance. Yellow-bellied Prinia and Plain Prinia rejected their own UV-blocked eggs in 18.2 and 8.3% of the experiments, respectively, and the difference was not significant. However, Yellow-bellied Prinia rejected 100% of the non-mimetic eggs, whereas the Plain Prinia rejected only 5%. Hence, UV reflectance alone is a cue in egg discrimination, but the importance of reflectance outside the UV spectrum in these two prinia species is much more responsive to selection as a consequence of brood parasitism. [ABSTRACT FROM AUTHOR]

Conspecific brood parasitism (CBP) is common in a variety of animal taxa, including birds. In coots (Fúlica spp.), and the closely related moorhens (Gallínula spp.), such parasitism is especially common, and hosts experience considerable costs through increased chick competition soon after hatching. Hence, these birds have evolved egg recognition and rejection abilities, e.g., egg counting, burying the foreign eggs, assigning them suboptimal positions within the mixed clutch, or deserting parasitized clutches. For common moorhens (Gallínula chloropus) it has been shown that desertion of parasitized nests pays most at the early egg laying stage. Later on, the costs of desertion exceed the costs of brood parasitism and acceptance is favoured. Here we tested moorhen egg discrimination behaviour during the incubation stage when acceptance of foreign eggs is expected. Four treatments were applied: (1) single added non-mimetic pale blue egg, (2) single added non-mimetic white chicken egg, (3) four foreign conspecific eggs added to the clutch and (4) four foreign conspecific eggs exchanged for four host eggs. Moorhens responded by egg destruction (47%) only to the increased clutch size but not to foreign egg colour and size match. In three nests where egg destruction occurred, all the eggs in the mixed clutch were destroyed by pecking, in two other nests one of the foreign eggs were pecked, while two other nests were deserted. These results are puzzling since moorhens have been shown to possess refined egg recognition abilities. To our knowledge, such destruction of parasitized clutches by moorhens during incubation has not previously been reported. We suggest that after clutch completion, moorhens use increase in clutch size as a cue to determine if they have been parasitized, and some individuals choose to reject parasitic eggs by deserting or destroying the whole clutch. [ABSTRACT FROM AUTHOR]

Avian brood parasites impose strong selection on their hosts leading to the evolution of antiparasite defenses like egg recognition and rejection. Discordance and template-based cognitive mechanisms may form the base for egg recognition by hosts. For discordance, hosts recognize eggs that constitute the minority in a clutch as alien, whereas in template-based recognition, hosts recognize eggs as alien when they do not match a template that can be innate or learnt. Template-based recognition by learning can be compromised in host species with polymorphic egg color like Paradoxornis parrotbills, hosts of the common cuckoo Cuculus canorus, because a male that learns an egg color in his first breeding attempt can subsequently mate with females having different colors and therefore reject his own eggs. We present a simple conceptual model to understand how an asymmetry in sex roles of care for eggs and egg polymorphism influence the evolution of egg recognition by hosts. We derive host reproductive success in the presence of variation in egg phenotype for both host and parasite. Our model shows that male recognition by learning is disadvantageous unless the host has monomorphic eggs. We suggest that interclutch variation in egg phenotype is the key to understanding the evolution of egg recognition and the sex involved. [ABSTRACT FROM PUBLISHER]

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]

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]

In the coevolutionary "arms race" between Common Cuckoos (Cuculus canorus) and their hosts, several adaptations and counter-adaptations have evolved. Here, we investigated natural parasitism and host sensitivity to egg rejection in Marsh Warblers (Acrocephalus palustris) in Bulgaria. The level of Common Cuckoo parasitism was high (28%), and average mimicry of Common Cuckoo eggs was good. Experimental parasitism with four egg-types that showed various degrees of mimicry of the host eggs revealed a generally high rejection rate of foreign eggs (37.5-100%). In addition, naturally laid Common Cuckoo eggs were rejected at a moderate rate (50%). The Marsh Warbler's ability to reject foreign eggs was strongly dependent on the degree of mimicry of the parasite egg but apparently not on differences in size between host and foreign eggs. Furthermore, intraclutch variation in host egg appearance was not related to the probability of egg rejection. The Marsh Warbler's highly developed egg-recognition ability and the good mimicry of Common Cuckoo eggs suggests that this poorly known host-parasite arms race has reached an advanced stage. The present study provides new insight into variables that are important for egg rejection in a heavily parasitized host population. [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.