Common Cuckoo Cuculus Canorus Research Articles

The cost of virulence: an experimental study of egg eviction by brood parasitic chicks

Hatchlings of some virulent brood parasitic birds have evolved to eliminate host offspring. We experimentally studied the dynamics and potential costs of the egg eviction behavior of hatchlings of the common cuckoo Cuculus canorus in broods of common redstarts Phoenicurus phoenicurus, a cavity nesting host. Eliminating the labor of egg tossing per se improved the cuckoo chick’s growth during the eviction period by ;20–30%. Evictor cuckoo chicks recovered from the cost of egg tossing to fledge at similar masses compared with solitary chicks, although they did so at older ages. Foster parents fed evictor chicks less often compared with nonevictors. Feeding frequencies by hosts to evictors correlated negatively with eviction effort as evicting chicks often appeared to ignore fosterers offering food. Nest cup steepness was negatively related to eviction success and positively to age at first eviction. We propose that eviction behavior by cuckoo hatchlings is favored by selection because the costs of eviction are much lower than the costs of cohabitation with host chicks. Key words: arms race, coevolution, host–parasite interactions. [Behav Ecol] ‘‘It is wonderful to see the extraordinary exertions of the young Cuckoo, when it is two or three days old, if a bird be put into the nest with it that is too weighty for it to lift out. In this state it seems ever restless and uneasy’’ (Jenner 1788, p. 226)

Evidence for egg discrimination preceding failed rejection attempts in a small cuckoo host

Given the high costs of avian obligate brood parasitism, host individuals are selected to reject parasitic eggs they recognize as foreign. We show that rejection may not necessarily follow egg discrimination when selective removal of the parasitic egg is difficult. We studied egg rejection behaviour in a small host of the common cuckoo Cuculus canorus, the eastern olivaceous warbler Hippolais pallida, by experimental parasitism with model and real non-mimetic cuckoo eggs and video recordings of host behaviour. Hosts pecked 87 per cent (20 out of 23) of the model eggs but eventually accepted 43.5 per cent (10 out of 23) of them. A similar pattern was found for real cuckoo eggs, which were all pecked, but as many as 47 per cent (7 out of 15) of them were accepted. To our knowledge, this is the first demonstration of a cuckoo host discriminating against real parasitic eggs but often accepting them. Our results also show that in host species experiencing difficulties in performing puncture ejection, non-mimetic cuckoo eggs may avoid rejection by means of their unusually high structural strength.

Begging Behavior of Fledgling Rusty-breasted Cuckoo (Cacomantis sepulcralis)

Abstract I describe previously unknown begging calls and displays of a fledgling Rusty-breasted Cuckoo (Cacomantis sepulcralis) fed by a Pied Fantail (Rhipidura javanica) in Singapore. The cuckoo emitted two types of begging calls: (1) ‘host-absent begging call’ (loud ‘tsi’ repeated at 1-sec intervals) and (2) ‘standard’ begging call in the presence of the Pied Fantail (wheezy ‘seeee’ repeated 1–2 times/sec). The fledgling also performed the ‘wing-shake begging’ display, i.e., it raised one of its wings at a time towards the approaching Pied Fantail. This display was similar to that of the best studied brood parasite, the Common Cuckoo (Cuculus canorus). The structure of both types of begging calls of the Rusty-breasted Cuckoo was different in comparison to the Common Cuckoo and relatively more similar to some other closely related species of the genus Cacomantis.

Choosing suitable hosts: common cuckoos Cuculus canorus parasitize great reed warblers Acrocephalus arundinaceus of high quality

We investigated the hypothesis that the common cuckoo Cuculus canorus selects host pairs of good phenotypic quality. As there is some evidence that cuckoos may select hosts within a population non-randomly based on external cues reflecting their foster abilities, we predicted that great reed warbler Acrocephalus arundinaceus pairs parasitized by the cuckoo would exhibit higher quality than unparasitized ones. To test this assumption, we evaluated two different parameters indicating host quality: body condition and characteristics of host eggs. We found that parasitized females showed significantly better body condition than unparasitized ones, and the model showed that the probability of being parasitized by the cuckoos increased with increasing body condition. Moreover, the likelihood of being parasitized by a cuckoo within the great reed warbler population increased with decreasing colour variability within clutches: parasitized females allocated costly blue pigments to eggshells more equally compared with unparasitized ones. Our study revealed that cuckoos parasitize great reed warbler females of higher quality, as reflected in host body condition and egg colour characteristics. In highly mimetic systems, cuckoos may choose to parasitize hosts with eggs displaying low intraclutch variation, both because this leads to reduced rejection and because these hosts are of high quality.

Egg rejection behaviour in the great reed warbler (Acrocephalus arundinaceus): the effect of egg type

Egg discrimination in hosts of the common cuckoo Cuculus canorus is frequently studied by experimental parasitism, using model cuckoo eggs. We compared egg rejection behaviour of the great reed warbler Acrocephalus arundinaceus to either model cuckoo eggs made of plastic or painted real host eggs. We simultaneously parasitised host nests by two different egg types to simulate cuckoo parasitism. A previous study revealed very similar, ca. 70%, rejection rates against both of these egg types (beige or bluish background colour maculated with dark brown) when they were used for single parasitism. In the present study we showed 96% average rejection rates against these egg types when they were applied in multiple experimental parasitism, causing a more predictable output for rejection behaviour. Hard plastic eggs and painted real eggs were rejected at similar frequencies, and videotaping revealed that model egg rejection caused extra work for great reed warblers. We revealed a new type of rejection behaviour, when hosts tried to eject hard-shelled model cuckoo eggs: Hosts made little holes in the middle part of these plastic eggs by pecking them several times before ejection, as if seeking the possibility to pierce and hold these eggs in their bills. Painted real eggs were rejected by actually puncturing the eggshell and holding them in the bill during ejection. No instances of grasp ejection were recorded during filming. Most experimental eggs of either type were ejected within 1 day after the introduction of the eggs, indicating that hosts made their rejection decisions quickly. Our observations suggest the lack of plasticity in the mode and timing of ejection behaviour towards experimental cuckoo eggs of different types in great reed warblers.

Individual female common cuckoosCuculus canoruslay constant egg types but egg appearance cannot be used to assign eggs to females

Females of the obligate brood parasitic common cuckoo Cuculus canorus are assumed to lay eggs of consistent colour and pattern and egg characteristics have been used to separate between different individuals. We tested the “constant egg-type hypothesis” in blind tests using test persons who grouped cuckoo eggs into “potential clutches” based on similarity in appearance. A correct classification of eggs laid by known (radiotagged) females supported the hypothesis. However, comparisons between maternity based on visual assessments and DNA-based parentage analyses revealed rather poor concordance between the two methods. Our findings indicate that egg characteristics cannot be used to separate between cuckoo females, even if they lay eggs with constant appearance. The reason is probably that there are only small or negligible variations in egg appearance between some females like mothers and daughters or other closely related individuals.

Predictors of resistance to brood parasitism within and among reed warbler populations

In the coevolutionary arms race between avian brood parasites and their hosts, several adaptations have evolved on both sides, the most prominent and important host defense being rejection of the parasitic egg. In the present study, we investigated possible predictors of egg rejection in 14 populations of reed warblers Acrocephalus scirpaceus across Europe differing in risk of parasitism by the common cuckoo Cuculus canorus, providing a test of factors associated with geographic variation in host resistance to parasitism. In a binomial general linear mixed model procedure, we quantified the possible influence of host clutch size, cuckoo parasitism in population (yes/no), height of the nest above ground, height of vegetation in the vicinity of the nest and distance to nearest vantage point on rejection of an experimentally added nonmimetic cuckoo sized egg. In addition, we entered ‘‘population’’ into the models as a random factor. Rejection rate varied significantly among populations (range 4.8–68.9%). The most parsimonious model, based on selection by the Akaike information criterion, included cuckoo parasitism in the population (yes/ no) and host clutch size; rejection rate was the highest in parasitized populations, and individuals laying larger clutches were the best rejecters. Furthermore, rejecters tended to breed in higher vegetation than acceptors. These findings suggest that spatial variation in the level of host resistance to brood parasitism may depend on current and/or past selection pressure due to the parasite and individual differences linked to abilities for egg rejection. Key words: Acrocephalus scirpaceus, brood parasitism, clutch size, coevolution, common cuckoo, Cuculus canorus, egg rejection, metapopulation, reed warbler. [Behav Ecol]

Gjøkparasittisme hos heipiplerke: Noen erfaringer fra Øyerfjellet sesongen 2005

In a mountainous area of Øyerfjellet 17 nests of the Meadow Pipit Anthus pratensis were found during the season of 2005. Five or possibly six of these nests were parasitized by the Common Cuckoo Cuculus canorus, giving a parasitizing rate of 29.4% and 35.3%, respectively. The nests were regularly controlled, and two nests were found deserted by the Meadow Pipit probably during the start of the nesting period, whereas three Cuckoo chicks were hatched. Nearly hatched eggs or newly hatched chicks were found ejected from these three Meadow Pipit nests. When comparing the egg clutches from parasitized nests with unparasitized nests, it was roughly estimated that a mean of 1 ½ Meadow Pipit eggs were missing in the parasitized nests. All the five Cuckoo eggs had a pale brownish colour. When considering this brownish colour, it was suggested that mimicry of the Meadow Pipit eggs and the Cuckoo egg were slightly better in the three nests of completed hatching than in the two nests being deserted. The pattern and markings of the eggs showed good mimicry between eggs of Meadow Pipit and Cuckoo except for the pigment concentration at the broad end of many Meadow Pipit eggs.

Getting rid of the cuckoo Cuculus canorus egg: why do hosts delay rejection?

Egg discrimination is well documented in many hosts of avian brood parasites, but the proximate mechanisms of egg recognition and rejection decisions are poorly understood. Relevant in this respect is the observation that rejectors of parasite eggs often delay their response. This delay has implications for understanding mechanisms important for egg recognition and is the main focus of the present study. We investigated experimentally the relative effects of egg mimicry and eggshell strength of common cuckoo Cuculus canorus eggs on the delay in rejection in marsh warblers Acrocephalus palustris. In addition, by video recording host responses, we elucidate the proximate mechanisms behind the delayed rejections. Host nests were experimentally parasitized with 3 types of real eggs differing in mimicry and/or eggshell strength. Both egg mimicry and eggshell strength significantly affected the time to rejection, but the effect of mimicry was dominant. The delayed rejection of mimetic eggs was explained by the existence of latency to the release of rejection behavior because of recognition problems. Second, when rejection response towards mimetic eggs was initiated, it was less intense compared with hosts experiencing nonmimetic eggs. Our results are consistent with the hypothesis that host motivation when confronted with mimetic eggs needs to increase above a certain threshold before rejection behavior is released, which likely minimizes the risk of recognition errors. An additional component of the delay in rejection as shown by hosts facing nonmimetic eggs was the seemingly inefficient host rejection behavior, probably reflecting lack of previous experience. Key words: brood parasitism, cuckoo, egg recognition, eggshell strength, marsh warbler, mimicry. [Behav Ecol]

Aspects of breeding ecology of the eastern olivaceous warbler (Hippolais pallida)

The breeding ecology of eastern olivaceous warblers Hippolais pallida is poorly known. In this study, we provide data on nest site selection and breeding parameters of the species in a population in northwestern Bulgaria, the only one known to be regularly and heavily parasitized by the common cuckoo Cuculus canorus (hereafter cuckoo). Eastern olivaceous warblers only bred within human settlements of the study area, avoiding seemingly suitable habitat outside them. Nests were built in a wide range of plant taxa but ailanthuses Ailanthus altissima and mulberries Morus spp. were most frequently used (21%). After taking into account the availability of vegetation, there was an apparent preference for several plant taxa but not for mulberries. Mean nest height was 1.65 ± 0.98 (0.53-7.60) m, n = 217, and it varied signifi- cantly among different types of nesting substrate. Laying date and clutch size of first breeding attempts averaged 10 June ± 0.98 days, n = 101 and 3.9 ± 0.07 (2-5) eggs, n = 72, respectively. Hatching success, fledging success, and breeding success were 42.5, 86.4, and 36.7%, respec- tively. The main sources of nest mortality were predation and cuckoo parasitism, with no significant difference in the proportion of nests lost to each. Cuckoo parasitism seemed responsible for the relatively low hatching success in this population.

Eviction behaviour of the common cuckoo Cuculus canorus chicks

We studied the eviction behaviour of common cuckoo Cuculus canorus chicks by video recording at nests of great reed warblers Acrocephalus arundinaceus and reed warblers Acrocephalus scirpaceus. There were no significant differences in hatching mass and age at first eviction between cuckoos reared by either host. However, mass at eviction had a significant effect on the timing of first eviction event. No significant difference in time required to evict was found between serial intranest eviction events for cuckoos raised by either host. However, “great reed warbler” cuckoos evicted significantly quicker than “reed warbler” cuckoos during particular eviction events. A majority (70%) of “reed warbler” cuckoos evicted during the day, while most “great reed warbler” cuckoos evicted nocturnally (63%). We did not find any effect of the temperature inside or outside the nest on eviction behaviour. Both “great reed warbler” and “reed warbler” cuckoos evicted regardless the fact whether a parent was absent or present at the nest. Interestingly, individual cuckoos were consistent in their eviction behaviour relative to host presence or absence; particular cuckoo chick evicted only when the parents were present or absent from the nest.

Factors influencing the risk of common cuckoo Cuculus canorus parasitism on marsh warblers Acrocephalus palustris

Factors influencing the risk of common cuckoo Cuculus canorus parasitism on marsh warblers Acrocephalus palustris

Eviction behaviour of the common cuckoo Cuculus canorus chicks

Eviction behaviour of the common cuckoo Cuculus canorus chicks

NEST LIGHT ENVIRONMENT AND THE POTENTIAL RISK OF COMMON CUCKOO (CUCULUS CANORUS) PARASITISM

Abstract Brood parasitism represents a significant cost in reproduction; thus, natural selection should favor the evolution of host defenses, which in turn may favor evolution of more sophisticated techniques by the parasite to overcome host defenses. These host defenses include egg rejection, attacking parasites near the nest, and avoiding parasitism by concealing nest sites. In all these antiparasitism strategies, nest light environment may play an important role. In the present study, the risk of Common Cuckoo (Cuculus canorus) parasitism for the Great Reed Warbler (Acrocephalus arundinaceus) was modeled in relation to the in situ nest light environment, from far ultraviolet (UV) to infrared (IR) radiation (280–1,100 nm), and nest situation and structure. The percentage of photosynthetically active radiation (PAR) plus IR radiation (400–1,100 nm) falling on the nest, maximum nest width, and distance between the nest and the nearest active conspecific neighbor were significantly related to the risk of p...

Evolution of Defence Portfolios in Exploiter–Victim Systems

Some organisms maintain a battery of defensive strategies against their exploiters (predators, parasites or parasitoids), while others fail to employ a defence that seems obvious. In this paper, we shall investigate the circumstances under which defence strategies might be expected to evolve. Brood parasites and their hosts provide our main motivation, and we shall discuss why the reed warbler Acrocephalus scirpaceus has evolved an egg-rejection but not a chick-rejection strategy as a defence against the common (Eurasian) cuckoo Cuculus canorus, while the superb fairy-wren Malurus cyaneus has evolved a chick-rejection but not an egg-rejection strategy as a defence against Horsfield's bronze-cuckoo Chrysococcyx basalis. We suggest that the answers lie in strategy-blocking, where one strategy (the blocking strategy) prevents the appearance of another (the blocked strategy) that would be adaptive in its absence. This may be common in exploiter-victim systems.

Environmental conditions influence egg color of reed warblers Acrocephalus scirpaceus and their parasite, the common cuckoo Cuculus canorus

The outer layer of the eggshell in birds is in many cases covered by pigments that are assumed to be genetically determined traits with a negligible environmental component. To test the hypothesis that spring environmental conditions (i.e., temperature and rainfall) may affect bird egg pigmentation, we measured by spectrophotometry and photography egg coloration and spottiness on reed warbler (Acrocephalus scirpaceus L.) clutches parasitized by the common cuckoo (Cuculus canorus L.) collected over a period of 24 years and preserved in the Zoological Museum, Copenhagen, Denmark. In addition, we investigated whether spring environmental conditions may influence the coevolutionary relationship between the cuckoo and its host via changes in cuckoo–host egg matching. Generalized mixed models revealed that reed warbler eggs were more brilliant in those springs with a higher rainfall and tended to be bluer and greener in springs with a lower relative temperature. On the other hand, cuckoo eggs were bluer and greener in springs with a higher rainfall. Cuckoo–host egg matching in blue-greenness and spottiness was better in springs with a higher rainfall. These results provide support for the existence of an environmental component on bird egg coloration and suggest that environmental factors may potentially affect the outcome of important features of the arms race between cuckoos and reed warblers.

Hopeless solicitation? Host-absent vocalization in the common cuckoo has no effect on feeding rate of reed warblers

Begging behavior of nestlings can signal both hunger and competitive ability. Studies of begging in evicting avian brood parasites exclude the influence of nestling competition and may provide new insights into the host–parasite conflict and the evolution of signaling. Apart from the begging call, common cuckoo Cuculus canorus nestlings use special vocal displays in the absence of their hosts, termed here host-absent vocalization (HAV). Since these conspicuous calls can increase the risk of predation and require energy, their costs should be balanced by some benefits, such as increased food provisioning. However, there has been no evidence that chicks convey information about their hunger by HAV. We therefore tested experimentally whether cuckoo chicks use HAV as an additional signal to enhance food-delivery rate by their hosts. We used playback of HAV recorded from cuckoo nestlings to determine whether their hosts, reed warblers Acrocephalus scirpaceus, increase their provisioning in response to an apparent increase in HAV. Older chicks spent more time in HAV than younger chicks, suggesting that HAV is not caused by inaccurate discrimination of host arrival stimuli. Negative correlation of HAV with feeding rate and mass gain between the two experiments suggested that hunger was the motivation of HAV. The playback experiment, however, did not prove that HAV affects host provisioning rate. We discuss possible reasons for this result and provide alternative explanations for HAV, such as creating a bond between the hosts and the parasitic young used later in the postfledging care.

High synchrony of egg laying in common cuckoos (Cuculus canorus) and their great reed warbler (Acrocephalus arundinaceus) hosts

Female common cuckoos Cuculus canorus lay eggs every other day and typically parasitise nests before the hosts complete their clutches. When laying strategy of the cuckoo is well-synchronised with that of the host, the reproductive success of the parasite may increase. In contrast, when parasitism frequencies are high, cuckoo females might be less able to find suitable nests of the desired stage and without any prior cuckoo eggs. Contrary to this prediction, we found high synchrony of laying patterns between cuckoos and their local primary host, the great reed warbler Acrocephalus arundinaceus, under unusually heavy brood parasitism (ca 64% parasitism frequency) on the Hungarian Great Plane. Although the laying activities of the hosts showed different temporal patterns in the 2 consecutive years studied, the cuckoos closely followed the patterns in each year. This occurred despite the arrival of the cuckoos at the study site 2–3 weeks earlier than the great reed warblers. The matching of laying patterns with those of the hosts suggests an adaptive response to both ensure optimal hatchability of the cuckoo eggs and to avoid multiple parasitism of the same nest even under heavy pressures of brood parasitism.

An exceptionally high diversity of hoverflies (Syrphidae) in the food of the reed warbler (Acrocephalus scirpaceus)

Despite being considered a classical example of protective Batesian mimicry hoverflies (Syrphidae) are known to be preyed upon by various passerines. The aim of the present study was to examine in detail food brought by reed warblers Acrocephalus scirpaceus to their nests to better understand the importance of hoverflies in the diet of small passerines. Using neck collars, 273 food samples containing 8,545 food items delivered to reed warbler and parasitic common cuckoo Cuculus canorus nestlings in warbler nests were recorded. The study was conducted during three breeding seasons in South Moravia, Czech Republic. An unusually high diversity of hoverflies was found — 27 species, including Mesembrius peregrinus (critically endangered species in the Czech Republic) and Mallota cimbiciformis (endangered species) — a new taxon to the Czech Republic. This indicates that nestling diet analyses may provide not only information on avian foraging behaviour but also important faunistic data. Thus, without the detailed identification to species level of material from foraging behaviour studies valuable scientific information may be lost. Overall dominance of Syrphidae was 3.7%, the most common species being Episyrphus balteatus (55.7%, n = 318). However, this number seriously underestimates the importance of hoverflies in the diet of reed warblers as hoverflies are one of the largest prey taken by warblers. Both larvae and pupae were rare, imagines strongly dominating (92.7%). Both specific wasp mimics (e.g., Chrysotoxum verrali) and bee mimics (e.g., Eristalis spp.) were not avoided by foraging reed warblers. The presence of a parasitic cuckoo chick did not affect host foraging behaviour with respect to overall dominance of hoverflies in the diet (warbler 3.3%, cuckoo 3.8%).

Responses of Parasitized And Unparasitized Common Redstart (Phoenicurus Phoenicurus) Populations Against Artificial Cuckoo Parasitism

AbstractBrood parasitism selects for defensive mechanisms that enhance host fitness. Therefore, host populations under different parasitism pressures may express different levels of defense against brood parasites. We tested the rejection responses of currently parasitized and unparasitized Common Redstart (Phoenicurus phoenicurus) populations in Finland to artificial Common Cuckoo (Cuculus canorus) eggs. We predicted a higher level of defense in the parasitized population, but in fact the rejection rate was higher in the nonparasitized population. Nonmimetic artificial eggs were rejected more often than mimetic ones. Desertion probability was higher in the nonparasitized population and was independent of artificial egg type. Common Redstarts in the parasitized population rejected the artificial eggs mostly through ejection, whereas desertion was a more frequent rejection method in the nonparasitized population. Our results suggest that current selection pressures from brood parasites do not always explain the current levels of defense.Respuestas de Poblaciones Parasitadas y No Parasitadas de Phoenicurus phoenicurus Contra el Parasitismo Artificial de Cuculus canorus