Host species determines egg size in Oriental cuckoo

© 2018 The Zoological Society of London.The Oriental cuckoo Cuculus optatus is an obligate brood parasite associated with species of the genus Phylloscopus. Four distinct phenotypes of Oriental cuckoo eggs, matching eggshell colour patterns of Arctic warbler Phylloscopus borealis, common chiffchaff (Siberian) P. collybita tristis, yellow-browed warbler P. inornatus and Pallas's leaf warbler P. proregulus, have been identified in the Russian part of its breeding area. We compared egg length, breadth and volume of Oriental cuckoo egg phenotypes with eggs of the corresponding hosts from three geographical regions in Russia: the Urals, Siberia and the Far East. We found significant oometric differences between Oriental cuckoo egg phenotypes. Egg breadth of each cuckoo group matched the egg breadth of the host species, while the length of cuckoo eggs did not match egg length in host species. Our results can be explained in terms of clutch geometry. An egg sticking out above the clutch is likely to be rejected by the host and so breadth should match the host's egg. This constrains cuckoos in maintaining large egg volumes, which are essential for providing a cuckoo chick with the energy required to eject the host eggs and chicks. An increased egg length might compensate for breadth constraints. We suggest that the size of cuckoo eggs might also be affected by parental care - when only one parent is involved in feeding, eggs need to be larger. This might explain why the longest cuckoo eggs belonged to the phenotype parasitizing the smallest host, Pallas's leaf warbler, where only one parent feeds the chicks. In our view, differences in egg sizes of Oriental cuckoo phenotypes provide evidence of their adaptations to brood parasitism on small leaf warbler species.Peer reviewe

The function of three main call types in common cuckoo

Acoustic signals play a key role in shaping the relationships in birds. Common cuckoos Cuculus canorus are known to produce various call types, but the function of these calls has only been studied recently. Here, we used a combination of field recordings (conducted in 2017) and playback experiments (conducted in 2018) to investigate the functional significance of common cuckoo calls. We found significant differences in the characteristics between male two-element ‘cu-coo’ and three-element ‘cu-cu-coo’ calls, with these two call types being used in different contexts. The three-element male ‘cu-cu-coo’ calls were associated with females emitting their ‘bubbling’ call. Playback experiments revealed that both males and females exhibit stronger responses to playing female “bubbling” calls than with the calls of Eurasian sparrowhawk (Accipter nisus) serving as a control suggesting a significant intraspecific communication function for this call type. However, we did not find any evidence to support mate attraction in male calls, as females were not stimulated by playback of male calls compared to sparrowhawk calls in the control group

Multiple Species of Cuckoos Are Superior Predictors of Bird Species Richness in Asia

The abundance and the presence of common cuckoos Cuculus canorus have been shown to predict species richness of birds across Europe, while there are no such analyses available for other continents where species richness of parasitic cuckoos is larger. Here, we tested whether species richness of birds increased with the number of cuckoo species in two study areas in China and one in Japan. We also tested whether species richness of birds can be predicted by the number of cuckoo individuals. Furthermore, we compared the strength of association between overall bird species richness and species richness of cuckoos, Paridae, Corvidae, and birds of prey. This is the first study demonstrating that cuckoo species richness is more strongly associated with overall bird species richness than richness of species belonging to other families, and rather than occurrence of a single cuckoo species, as already demonstrated for the common cuckoo in Europe. The number of cuckoo species was positively associated with both non‐host and host species richness. We found evidence of the number of cuckoo species being associated with species richness of birds independently of country and year, while abundance of individual cuckoos was not a statistically significant predictor. Furthermore, we showed that richness of host species is strongly positively correlated with overall bird species richness in both countries. This implies that the high species richness of cuckoos in South‐East Asia is a reliable predictor of overall bird species richness

Identification of vocal individuality in male cuckoos using different analytical techniques

© 2017 The Author(s). Background: Individuality in vocalizations may provide an effective tool for surveying populations of the Common Cuckoo (Cuculus canorus) but there remains few data on which technique to use to identify individuality. In this research, we compared the within- and between-individual variation in cuckoo calls using two different analytical methods, and discuss the feasibility of using call individuality to count male cuckoos within a population. Methods: We recorded vocalization from 13 males, and measured 15 spectro-temporal variables for each call. The majority of these call variables (n=12) have greater variation between individuals than within individual. We first calculated the similarity (Pearson's R) for each paired calls in order to find a threshold that could distinguish calls emitted from the same or different males, and then counted the number of males based on this distinction. Second, we used the more widely accepted technique of discriminant function analysis (DFA) to identify individual male cuckoos, and compared the correct rate of classifying individuals between the two analytical methods. Results: Similarity of paired calls from the same male was significantly higher than from different males. Under a relatively broad threshold interval, we achieved a high ( > 90%) correct rate to distinguish calls and an accurate estimate of male numbers. Based on banded males (n=3), we found the similarity of paired calls from different days was lower when compared with paired calls from the same day, but this change did not obscure individual identification, as similarity values of paired calls from different days were still larger than the threshold used to distinguish calls from the same or different males. DFA also yielded a high rate (91.9%) of correct classification of individuals. Conclusions: Our study suggests that identifying individual vocalizations can form the basis of an appropriate survey method for counting male cuckoos within a population, provided the performance of different analytical techniques are compared

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Data from: Brain size in birds is related to traffic accidents

Estimates suggest that perhaps a quarter of a billion birds are killed by traffic annually across the world. This is surprising because birds have been shown to learn speed limits. Birds have also been shown to adapt to the direction of traffic and lane use, and this apparently results in reduced risks of fatal traffic accidents. Such behavioural differences suggest that individual birds that are not killed in traffic should have larger brains for their body size. We analysed the link between being killed by traffic and relative brain mass in 3521 birds belonging to 251 species brought to a taxidermist. Birds that were killed in traffic indeed had relatively smaller brains, while there was no similar difference for liver mass, heart mass or lung mass. These findings suggest that birds learn the behaviour of car drivers, and that they use their brains to adjust behaviour in an attempt to avoid mortality caused by rapidly and predictably moving objects