Rejection of parasitic eggs in relation to egg appearance in magpies

The coevolutionary process between avian brood parasites and their hosts predicts that low intraclutch variation in egg colour appearance favours egg discrimination of parasite eggs by hosts. Low intraclutch variation would also result in high interclutch variation, which would increase the difficulty of evolution of mimicry by the cuckoo, because many host colour patterns might coexist in the same host population. We explored this possibility using an experimental approach in the common magpie, Pica pica, and great spotted cuckoo, Clamator glandarius, system. We artificially parasitized magpie nests with great spotted cuckoo model eggs to assess host response in two populations in Spain (Guadix and Doñana) in relation to intraclutch variation in egg appearance, measured by ultraviolet-visible reflectance spectrophotometry. Individuals that rejected model cuckoo eggs had higher intraclutch variation than accepters, suggesting that an increase, rather than a decrease, in intraclutch variation in magpie egg appearance was advantageous for cuckoo egg discrimination.     

Avian vision and the evolution of egg color mimicry in the common cuckoo

Coevolutionary arms races are a potent force in evolution, and brood parasite-host dynamics provide classical examples. Different host-races of the common cuckoo, Cuculus canorus, lay eggs in the nests of other species, leaving all parental care to hosts. Cuckoo eggs often (but not always) appear to match remarkably the color and pattern of host eggs, thus reducing detection by hosts. However, most studies of egg mimicry focus on human assessments or reflectance spectra, which fail to account for avian vision. Here, we use discrimination and tetrachromatic color space modeling of bird vision to quantify egg background and spot color mimicry in the common cuckoo and 11 of its principal hosts, and we relate this to egg rejection by different hosts. Egg background color and luminance are strongly mimicked by most cuckoo host-races, and mimicry is better when hosts show strong rejection. We introduce a novel measure of color mimicry-"color overlap"-and show that cuckoo and host background colors increasingly overlap in avian color space as hosts exhibit stronger rejection. Finally, cuckoos with better background color mimicry also have better pattern mimicry. Our findings reveal new information about egg mimicry that would be impossible to derive by the human eye.     

Change in host rejection behavior mediated by the predatory behavior of its brood parasite

Passerine hosts of parasitic cuckoos usually vary in their abilityto discriminate and reject cuckoo eggs. Costs of discriminationand rejection errors have been invoked to explain the maintenanceof this within-population variability. Recently, enforcementof acceptance by parasites has been identified as a rejectioncost in the magpie (Pica pica) and its brood parasite, the greatspotted cuckoo (Clamator glandarius). Previous experimentalwork has shown that rejecter magpies suffer from increased nestpredation by the great spotted cuckoo. Cuckoo predatory behavioris supposed to confer a selective advantage to the parasitebecause magpies experiencing a reproductive failure may providea second opportunity for the cuckoo to parasitize a replacementclutch. This hypothesis implicitly assumes that magpies modulatetheir propensity to reject parasite eggs as a function of previousexperience. We tested this hypothesis in a magpie populationbreeding in study plots varying in parasitism rate. Magpie pairs thatwere experimentally parasitized and had their nests depredated,after their rejection behavior had been assessed, changed theirbehavior from rejection to acceptance. The change in host behaviorwas prominent in study plots with high levels of parasitism,but not in plots with rare or no cuckoo parasitism. We discussthree possible explanations for these differences, concludingthat in study plots with a high density of cuckoos, the probability fora rejecter magpie nest of being revisited and depredated bya cuckoo is high, particularly for replacement clutches, and,therefore, the cost for magpies of rejecting a cuckoo egg ina replacement clutch is increased. Moreover, in areas with highlevels of host defense (low parasitism rate), the probabilityof parasitism and predation of rejecter-magpie nests by thecuckoo is reduced in both first and replacement clutches. Therefore,rejecter magpies in such areas should not change their rejectionbehavior in replacement clutches.     

Imperfect mimicry of host begging calls by a brood parasitic cuckoo: a cue for nestling rejection by hosts?

Coevolutionary interactions between avian brood parasites and their hosts often lead to the evolution of discrimination and rejection of parasite eggs or chicks by hosts based on visual cues, and the evolution of visual mimicry of host eggs or chicks by brood parasites. Hosts may also base rejection of brood parasite nestlings on vocal cues, which would in turn select for mimicry of host begging calls in brood parasite chicks. In cuckoos that exploit multiple hosts with different begging calls, call structure may be plastic, allowing nestlings to modify their calls to match those of their various hosts, or fixed, in which case we would predict either imperfect mimicry or divergence of the species into host-specific lineages. In our study of the little bronze-cuckoo (LBC) Chalcites minutillus and its primary host, the large-billed gerygone Gerygone magnirostris, we tested whether: (1) hosts use nestling vocalizations as a cue to discriminate cuckoo chicks; (2) cuckoo nestlings mimic the host begging calls throughout the nestling period; and (3) the cuckoo begging calls are plastic, thereby facilitating mimicry of the calls of different hosts. We found that the begging calls of LBCs are most similar to their gerygone hosts shortly after hatching (when rejection by hosts typically occurs) but become less similar as cuckoo chicks get older. Begging call structure may be used as a cue for rejection by hosts, and these results are consistent with gerygone defenses selecting for age-specific vocal mimicry in cuckoo chicks. We found no evidence that LBC begging calls were plastic.     

How to evade a coevolving brood parasite: egg discrimination versus egg variability as host defences

Arms races between avian brood parasites and their hosts often result in parasitic mimicry of host eggs, to evade rejection. Once egg mimicry has evolved, host defences could escalate in two ways: (i) hosts could improve their level of egg discrimination; and (ii) negative frequency-dependent selection could generate increased variation in egg appearance (polymorphism) among individuals. Proficiency in one defence might reduce selection on the other, while a combination of the two should enable successful rejection of parasitic eggs. We compared three highly variable host species of the Afrotropical cuckoo finch Anomalospiza imberbis, using egg rejection experiments and modelling of avian colour and pattern vision. We show that each differed in their level of polymorphism, in the visual cues they used to reject foreign eggs, and in their degree of discrimination. The most polymorphic host had the crudest discrimination, whereas the least polymorphic was most discriminating. The third species, not currently parasitized, was intermediate for both defences. A model simulating parasitic laying and host rejection behaviour based on the field experiments showed that the two host strategies result in approximately the same fitness advantage to hosts. Thus, neither strategy is superior, but rather they reflect alternative potential evolutionary trajectories.     

Attractive blue‐green egg coloration and cuckoo−host coevolution

Recent evidence suggests that blue‐green coloration of bird eggshells may be related to female and/or egg phenotypic quality, and that such colour may affect parental effort and therefore the nutritional environment of developing nestlings. Here we suggest that these relationships and the signal function of eggshell coloration would affect the outcome of coevolution between avian brood parasites and their hosts in at least three different non‐exclusive evolutionary pathways. First, by laying blue‐green coloured eggs, cuckoo females may exploit possible sensory biases of their hosts, constraining the evolution of parasitic egg recognition, and thus avoid rejection. Second, because of the relatively high costs of laying blue eggs, cuckoo females may be limited in their ability to mimic costly blue‐green eggs of their hosts because cuckoo females lay many more eggs than their hosts. Furthermore, costs associated with foreign egg recognition errors would be relatively higher for hosts laying blue eggs. Third, cuckoos may use coloration of host eggs for selecting individuals or specific hosts of appropriate phenotypic quality (i.e. parental abilities). We here explored some predictions emerging from the above scenarios and found partial support for two of them by studying egg coloration of European cuckoos (Cuculus canorus) and that of their 25 main hosts, as well as parasitism and rejection rate of hosts. Cuckoo hosts parasitized with more blue, green, and ultraviolet cuckoo eggs, or those laying more blue‐green eggs, were more prone to accept experimental parasitism with artificial cuckoo eggs. In addition, coloration of cuckoo eggs is more variable when parasitizing hosts laying bluer‐greener eggs, even after controlling for the effect of host egg coloration (i.e. degree of egg matching). Globally, our results are consistent with the proposed hypothesis that host egg traits that are related to phenotypic quality of hosts, such as egg coloration, may have important implications for the coevolutionary interaction between hosts and brood parasites. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 154–168.     

Antagonistic antiparasite defenses: nest defense and egg rejection in the magpie host of the great spotted cuckoo

Brood parasites dramatically reduce the reproductive successof their hosts, which therefore have developed defenses againstbrood parasites. The first line of defense is protecting thenest against adult parasites. When the parasite has successfullyparasitized a host nest, some hosts are able to recognize andreject the eggs of the brood parasite, which constitutes the secondline of defense. Both defense tactics are costly and would be counteractedby brood parasites. While a failure in nest defense implies successfulparasitism and therefore great reduction of reproductive successof hosts, a host that recognizes parasitic eggs has the opportunityto reduce the effect of parasitism by removing the parasiticegg. We hypothesized that, when nest defense is counteractedby the brood parasite, hosts that recognize cuckoo eggs shoulddefend their nests at a lower level than nonrecognizers becausethe former also recognize adult cuckoos. Magpie (Pica pica) hoststhat rejected model eggs of the brood parasitic great spottedcuckoo (Clamator glandarius) showed lower levels of nest defensewhen exposed to a great spotted cuckoo than when exposed toa nest predator (a carrion crow Corvus corone). Moreover, magpiesrejecting cuckoo eggs showed lower levels of nest defense againstgreat spotted cuckoos than nonrecognizer magpies, whereas differencesin levels of defense disappeared when exposed to a carrion crow.These results suggest that hosts specialize in antiparasitedefense and that different kinds of defense are antagonistically expressed.We suggest that nest-defense mechanisms are ancestral, whereasegg recognition and rejection is a subsequent stage in the coevolutionaryprocess. However, host recognition ability will not be expressedwhen brood parasites break this second line of defense.     

MAGPIE HOST MANIPULATION BY GREAT SPOTTED CUCKOOS: EVIDENCE FOR AN AVIAN MAFIA?

Why should the hosts of brood parasites accept and raise parasitic offspring that differ dramatically in appearance from their own? There are two solutions to this evolutionary enigma. (1) Hosts may not yet have evolved the capability to discriminate against the parasite, or (2) parasite-host systems have reached an evolutionary equilibrium. Avian brood parasites may either gain renesting opportunities or force their hosts to raise parasitic offspring by destroying or preying upon host eggs or nestlings following host ejection of parasite offspring. These hypotheses may explain why hosts do not remove parasite offspring because only then will hosts avoid clutch destruction by the cuckoo. Here we show experimentally that if the egg of the parasitic great spotted cuckoo Clamator glandarius is removed from nests of its magpie Pica pica host, nests suffer significantly higher predation rates than control nests in which parasite eggs have not been removed. Using plasticine model eggs resembling those of magpies and observations of parasites, we also confirm that great spotted cuckoos that have laid an ejected egg are indeed responsible for destruction of magpie nests with experimentally ejected parasite eggs. Cuckoos benefit from destroying host offspring because they thereby induce some magpies to renest and subsequently accept a cuckoo egg.     

CUCKOO HOSTS SHIFT FROM ACCEPTING TO REJECTING PARASITIC EGGS ACROSS THEIR LIFETIME

One of the best‐known outcomes of coevolution between species is the rejection of mimetic parasite eggs by avian hosts, which has evolved to reduce costly cuckoo parasitism. How this behavioral adaptation varies along the life of individual hosts remains poorly understood. Here, we identify for the first time, lifetime patterns of egg rejection in a parasitized long‐lived bird, the magpie Pica pica and show that, during the years they were studied, some females accept, others reject, and some others modify their response to model eggs, in all cases switching from acceptance to rejection. Females tested in their first breeding attempt always accepted the model egg, even those individuals whose mothers were egg rejecters. A longitudinal analysis showed that the probability of egg rejection increased with the relative age of the female, but was not related to the risk of parasitism in the population. We conclude that ontogeny plays a fundamental role in the process leading to egg rejection in magpies.     

Host and brood parasite coevolutionary interactions covary with comparative patterns of the avian visual system

In coevolutionary arms-races, reciprocal ecological interactions and their fitness impacts shape the course of phenotypic evolution. The classic example of avian host–brood parasite interactions selects for host recognition and rejection of increasingly mimetic foreign eggs. An essential component of perceptual mimicry is that parasitic eggs escape detection by host sensory systems, yet there is no direct evidence that the avian visual system covaries with parasitic egg recognition or mimicry. Here, we used eye size measurements collected from preserved museum specimens as a metric of the avian visual system for species involved in host–brood parasite interactions. We discovered that (i) hosts had smaller eyes compared with non-hosts, (ii) parasites had larger eyes compared with hosts before but not after phylogenetic corrections, perhaps owing to the limited number of independent evolutionary origins of obligate brood parasitism, (iii) egg rejection in hosts with non-mimetic parasitic eggs positively correlated with eye size, and (iv) eye size was positively associated with increased avian-perceived host–parasite eggshell similarity. These results imply that both host-use by parasites and anti-parasitic responses by hosts covary with a metric of the visual system across relevant bird species, providing comparative evidence for coevolutionary patterns of host and brood parasite sensory systems.     

Rejection of cuckoo (Cuculus canorus) eggs by meadow pipits (Anthus pratensis)

Meadow pipits (Anthus pratensis) normally accept mimetic cuckoo(Cuculus canorus) eggs laid in their nests. In field experimentsin which a mimetic or a nonmimetic model cuckoo egg was placedin meadow pipit nests, those hosts that were simultaneouslypresented with a cuckoo dummy mounted beside the nest showeda significantly higher ability to recognize and reject (normallyby desertion) the parasite's egg than those that were not presentedwith the dummy. In the present study we sought to answer thequestion of why meadow pipits do not always (i.e., even whenno cuckoo was visible) reject cuckoo eggs. The results fromthe field experiments provide support for a theory that two"brood parasite" stimuli (a cuckoo egg in the nest and a cuckoonear the nest) are necessary to induce the meadow pipits toreject cuckoo eggs. When the threshold for rejection had beenreached, the hosts reacted in a relatively short time afterthey were faced with the parasite stimuli. The results of theseexperiments also showed that a significantly higher rate ofrejection occurred earlier rather than later in the incubationperiod. A possible explanation for the higher rate of acceptanceof model cuckoo eggs among meadow pipits in Norway comparedto those in Britain is discussed.     

Egg rejection by Iberian azure-winged magpies Cyanopica cyanus in the absence of brood parasitism

The Iberian azure-winged magpie Cyanopica cyanus shows a remarkable ability to discriminate against great spotted cuckoo Clamator glandarius eggs. Here, I studied whether egg recognition in this species could be a derived feature resulting from intra-specific brood parasitism. Azure-winged magpies showed a very high level of discrimination and rejection of great spotted cuckoo models (73.7%), and of conspecific eggs (42.8%), even when no evidence of great spotted cuckoo or conspecific brood parasitism has been found in the population. Azure-winged magpie discriminated more readily than magpies, the current favourite host of the great spotted cuckoo. The high rejection rate of conspecific eggs by the azure-winged magpie suggests that it is quite possible that egg discrimination in this species evolved in response to conspecific brood parasitism rather than to cuckoo parasitism.     

Evolution of host egg mimicry in a brood parasite, the great spotted cuckoo

Brood parasitism in birds is one of the best examples of coevolutionary interactions in vertebrates. Coevolution between hosts and parasites is assumed to occur because the parasite imposes strong selection pressures on its hosts, reducing their fitness and thereby favouring counter-adaptations (e.g. egg rejection) which, in turn, select for parasite resistance (e.g. egg mimicry). Great spotted cuckoos ( Clamator glandarius ) are usually considered a brood parasite with eggs almost perfectly mimicking those of their host, the magpie ( Pica pica ). However, Cl. glandarius also exploits South African hosts with very different eggs, both in colour and size, while the Cl. glandarius eggs are similar to those laid in nests of European hosts. Here, we used spectrophotometric techniques for the first time to quantify mimicry of parasitic eggs for eight different host species. We found: (1) non-significant differences in appearance of Cl. glandarius eggs laid in nests of different host species, although eggs laid in South Africa and Europe differed significantly; (2) contrary to the general assumption that Cl. glandarius eggs better mimic those of the main host in Europe ( P. pica ), Cl. glandarius eggs more closely resembled those of the azure-winged magpie ( Cyanopica cyana ), a potential host in which there is no evidence of recent parasitism; (3) the appearance of Cl. glandarius eggs was not significantly related to the appearance of host eggs. We discuss three possible reasons why Cl. glandarius eggs resemble eggs of some of their hosts. We suggest that colouration of Cl. glandarius eggs is an apomorphic trait, and that variation between eggs laid in South African and European host nests is due to genetic isolation among these populations and not due to variation in colouration of host eggs.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 551–563.     

Discrimination and ejection of eggs and nestlings by the fan-tailed gerygone from New Caledonia

Nestling rejection is a rare type of host defense against brood parasitism compared with egg rejection. Theoretically, host defenses at both egg and nestling stages could be based on similar underlying discrimination mechanisms but, due to the rarity of nestling rejector hosts, few studies have actually tested this hypothesis. We investigated egg and nestling discrimination by the fan-tailed gerygone Gerygone flavolateralis, a host that seemingly accepts nonmimetic eggs of its parasite, the shining bronze-cuckoo Chalcites lucidus, but ejects mimetic parasite nestlings. We introduced artificial eggs or nestlings and foreign gerygone nestlings in gerygone nests and compared begging calls of parasite and host nestlings. We found that the gerygone ejected artificial eggs only if their size was smaller than the parasite or host eggs. Ejection of artificial nestlings did not depend on whether their color matched that of the brood. The frequency of ejection increased during the course of the breeding season mirroring the increase in ejection frequency of parasite nestlings by the host. Cross-fostered gerygone nestlings were frequently ejected when lacking natal down and when introduced in the nest before hatching of the foster brood, but only occasionally when they did not match the color of the foster brood. Begging calls differed significantly between parasite and host nestlings throughout the nestling period. Our results suggest that the fan-tailed gerygone accepts eggs within the size range of gerygone and cuckoo eggs and that nestling discrimination is based on auditory and visual cues other than skin color. This highlights the importance of using a combined approach to study discrimination mechanisms of hosts.     

Brood parasitism is associated with increased bacterial contamination of host eggs: bacterial loads of host and parasitic eggs

Factors related to bacterial environment of nests are of primary interest for understanding the causes of embryo infection and the evolution of antimicrobial defensive traits in birds. Nest visitors such as parasites could act as vectors for bacteria and/or affect the hygienic conditions of nests and hence influence the nest bacterial environment. In the present study, we explored some predictions of this hypothetical scenario in the great spotted cuckoo (Clamator glandarius)–magpie (Pica pica) system of brood parasitism. Great spotted cuckoos visit the nests of their magpie hosts and frequently damage some of the host eggs when laying eggs or on subsequent visits. Therefore, it represents a good system for testing the effect of nest visitors on the bacterial environment of nests. In accordance with this hypothesis, we found that the bacterial load of magpie eggshells was greater in parasitized nests, which may suggest that brood parasitism increases the probability of bacterial infection of magpie eggs. Moreover, comparisons of bacterial loads of cuckoo and magpie eggs revealed that: (1) cuckoo eggshells harboured lower bacterial densities than those of their magpie hosts in the same nests and (2) the prevalence of bacteria inside unhatched eggs was higher for magpies than for great spotted cuckoos. These interspecific differences were predicted because brood parasitic eggs (but not host eggs) always experience the bacterial environments of parasitized nests. Therefore, the results obtained in the present study suggest that parasitic eggs are better adapted to environments with a high risk of bacterial contamination than those of their magpie hosts. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 836–848.     

Egg colour mimicry in the common cuckoo Cuculus canorus as revealed by modelling host retinal function

Some parasite cuckoo species lay eggs that, to the human eye, appear to mimic the appearance of the eggs of their favourite hosts, which hinders discrimination and removal of their eggs by host species. Hitherto, perception of cuckoo-host egg mimicry has been estimated based on human vision or spectrophotometry, which does not account for what the receivers' eye (i.e. hosts) actually discriminates. Using a discrimination model approach that reproduces host retinal functioning, and museum egg collections collected in the south of Finland, where at least six different races of the European cuckoo (Cuculus canorus) coexist, I first assess whether the colour design of cuckoo eggs of different races maximizes matching for two favourite avian hosts, viz. the redstart (Phoenicurus phoenicurus) and the pied wagtail (Motacilla alba). Second, I assess the role of nest luminosity on host perception of mimicry by the same two hosts. Phoenicurus-cuckoo eggs showed a better chromatic matching with the redstart-host eggs than other cuckoo races, and in most cases can not be discriminated. Sylvia-cuckoo eggs, however, showed better achromatic matching with redstart-host eggs than Phoenicurus-cuckoo eggs. Also, Motacilla-cuckoo eggs showed poorer chromatic and achromatic matching with pied wagtail-host eggs than Sylvia-cuckoo eggs. Nest luminosity affected chromatic and achromatic differences between cuckoo and host eggs, although only minimally affected the proportion of cuckoo eggs discriminated by chromatic signals. These results reveal that cuckoo races as assessed by humans do not entirely match with host perception of matching and that achromatic mechanisms could play a main role in the discrimination of cuckoo eggs at low-light levels.     

Great Spotted Cuckoos Frequently Lay Their Eggs While Their Magpie Host is Incubating

Species that suffer from brood parasitism face a considerable reduction in their fitness which selects for the evolution of host defences. To prevent parasitism, hosts can mob or attack brood parasites when they approach the host nest and block the access to the nest by sitting on the clutch. In turn, as a counter‐adaptation, brood parasites evolved secretive behaviours near their host nests. Here, we have studied great spotted cuckoo (Clamator glandarius) egg‐laying behaviour and defence by their magpie (Pica pica) hosts inside the nest using continuous video recordings. We have found several surprising results that contradict some general assumptions. The most important is that most (71%) of the parasitic events by cuckoo females are completed while the magpie females are incubating. By staying in the nest, magpies force cuckoo females to lay their egg facing the high risk of being attacked by the incubating magpie (attack occurred in all but one of the events, n = 15). During these attacks, magpies pecked the cuckoo violently, but could never effectively avoid parasitism. These novel observations expand the sequence of adaptations and counter‐adaptations in the arms race between brood parasites and their hosts during the pre‐laying and laying periods.     

The evolution of egg size in the brood parasitic cuckoos

We compared genera of nonparasitic cuckoos and two groups ofparasitic cuckoos: those raised together with host young ("nonejectors")and those in which the newly hatched cuckoo either ejects thehost eggs or chicks, or kills the host young ("ejectors"). Nonejectorsare similar to their hosts in body size and parasitize largerhosts than do ejectors, which parasitize hosts much smallerthan themselves. In both types of parasite, the cuckoo's eggtends to match the host eggs in size. To achieve this, nonejectorshave evolved a smaller egg for their body size than have nonparasiticcuckoos, and ejectors have evolved an even smaller egg. Amongejector cuckoo genera, larger cuckoos have larger eggs relativeto the eggs of their hosts, and the relationship between cuckooegg volume (mass of the newly-hatched cuckoo) and host egg volume(mass to be ejected) did not differ from that predicted by weight-liftingallometry. However, comparing among Cuculus cuckoo species,the allometric slope differed from the predicted, so it is notclear that egg size is related to the need to give the cuckoochick sufficient strength for ejection. Comparing the two mostspeciose ejector genera, Chrysococcyx cuckoos (smaller and parasitizedome-nesting hosts) lay eggs more similar in size to their host'seggs than do Cuculus cuckoos (larger and parasitize open cup–nestinghosts). Closer size-matching of host eggs in Chrysococcyx mayreflect the following: (1) selection to reduce adult body massto facilitate entry through small domed nest holes to lay, and(2) less need for a large egg, because longer incubation periodsin dome-nesting hosts allow the young cuckoo more time to growbefore it need eject host eggs.     

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

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.     

Climatic effects and phenological mismatch in cuckoo–host interactions: a role for host phenotypic plasticity in laying date?

Climatic effects on breeding phenology vary across organisms and therefore might promote a phenological mismatch in ecologically interacting species, including those engaged in coevolutionary interactions such as brood parasites and their hosts. Recent studies suggest that climatic induced changes in migration phenology may have mismatched cuckoos and their hosts in Europe. However, it is currently unknown whether cuckoo–host phenological mismatch results from different degrees of phenotypic plasticity or to different speeds of microevolutionary processes affecting hosts and parasites. Here we performed 1) cross‐sectional correlations between climate conditions and population level of phenological mismatch between the migratory brood parasite great spotted cuckoo Clamator glandarius and its main resident host in Europe, the magpie Pica pica; and 2) a longitudinal analysis to study within‐individual variation in breeding phenology for individual hosts experiencing different climate conditions over a period of nine years (2005–2013). Cross‐sectional analyses revealed independent and contrary effects of winter and spring temperature on magpie phenology: magpie hosts tend to breed earlier those years with lower February temperatures, however, high temperature in the first half of April spur individuals to lay eggs. Breeding phenology of cuckoos was tuned to that of their magpie host in time and duration. However, annual phenological mismatch between cuckoos and magpie hosts increased with NAO index and January temperature. Longitudinal analyses revealed high individual consistency in magpie host phenology, but a low influence of climate, suggesting that the climatic‐driven phenological mismatch between cuckoos and magpies at the population‐level cannot be explained by a host plastic response to climatic conditions.