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Many species mob predators to drive them away. Mobbing carries personal risk, but the risk of injury or death declines and the likelihood of repelling the predator increases in larger groups. The capacity to evaluate the number of mobbers before joining a mobbing group may be highly beneficial for individuals when deciding to join. Although recent studies have found that birds can use individual vocal discrimination to assess the number of conspecifics involved in initiating mobbing events, it is little known whether birds are able to evaluate the number of heterospecific mobbers. In this study, we investigated whether the number of heterospecifics responding to mobbing calls of Great Tits Parus major was influenced by the number of callers (a mix of Great Tit callers simulated by playbacks and live Great Tits attracted to playbacks, range one to seven callers). The total number of responding heterospecific individuals and species was positively influenced by the total number of callers, with heterospecifics responding more to larger than smaller Great Tit groups. However, these results may be driven by the total number of calls, call overlap and increased noise generated by the additional mobbers, and not the number per se. These findings therefore allow us to assess whether birds are more inclined to join a mobbing group when it consists of more heterospecific callers, but we cannot tell whether birds use individual vocal discrimination to assess the number of heterospecific callers. [ABSTRACT FROM AUTHOR]

Many bird species defend their territories against conspecifics during the breeding season. Although some temperate species have been observed to defend territories outside of the breeding season, such cases are rarely noted in the literature, and it remains largely unknown which environmental factors influence such behaviour. In this study, we investigated non-breeding territorial behaviour in the Eurasian nuthatch (Sitta europaea). Territorial responses were elicited with a simulated territory intrusion (playbacks of calls combined with a wooden model of nuthatch) in autumn, winter and spring. Territorial responses did not differ between autumn and winter but differed between the autumn/winter and spring; they declined until about mid-December (winter) and increased after that into the spring. We found an increase in territorial responses with increasing photoperiod (day length) in autumn and with decreasing ambient temperature during spring. Our study provides novel evidence about non-breeding territorial behaviour in temperate birds and indicates that this behaviour is influenced by environmental factors. [ABSTRACT FROM AUTHOR]

The ability to discriminate between individuals or classes of individuals based on distinctive cues is considered a vital skill in cooperative and territorial species. Here, we used playback experiments to determine whether Western Australian Magpies Gymnorhina tibicen dorsalis discriminate between the territorial carolling calls of intra‐group and extra‐group conspecifics. Magpies responded more strongly to the playback of carolling calls from extra‐group individuals than to the playback of carolling calls from intra‐group individuals, spending more time vigilant and carolling in response to extra‐group carols. Our results suggest Western Australian Magpies are able to distinguish between individuals within and outside of their social group using only vocal signals and expands on growing research reporting vocal discrimination and individual recognition abilities across species. [ABSTRACT FROM AUTHOR]

Many animals produce antipredator calls in response to the presence of a predator, which, in some species, can provide information about the distance to predator. Although previous research has shown that several bird species are able to encode information about predator distance in their calls, such information is still lacking for a range of species. Moreover, most previous research has categorised the distance between the caller and the predator in two classes (close and far), but subtle acoustic variation can occur within each distance class. We investigate whether calls given by the Western Australian magpie varied according to predator distance. By presenting a taxidermied predator to a population of magpies at different distances, we found that calls varied according to predator distance from the caller, with more calls being produced when the predator was closer. In addition, we found that calls given in response to a predator nearby are acoustically different from those given in response to the same predator further away. This way of encoding information may allow prey to more efficiently moderate antipredator behaviours according to the level of threat. [ABSTRACT FROM AUTHOR]

Batesian mimicry refers to a harmless species protecting itself from predators by mimicking a harmful species. A case of acoustic Batesian mimicry has been proposed in the naturalist literature: it is suspected that birds called like a snake when disturbed in their cavities to deter mammalian predators or repel competitors. To evaluate this hypothesis, we first test the assumption that the hissing sound produced by adult females of a wild cavity-nesting species – the blue tit (Cyanistes caeruleus) – is acoustically similar to the hisses of three wild sympatric snake species. Then, we tested one prediction of this hypothesis which is that the receiver of the signal should react similarly to the snake and bird hisses. To do so, we used, hiss-naïve individuals, without any past experience with predators: the house mouse (Mus musculus domesticus), representing a model of a possible nest competitor. We quantified mouse responses to blue tit and snake hisses and two non-hiss sounds (other blue tit vocalizations and human voices). Our results show that snake hisses and blue tit hisses are structurally more similar to each other than to other blue tit vocalizations and that both hisses provoke comparable levels of anxiety behavior in mice. Taken together, these results are compatible with the hypothesis that blue tits have evolved to mimic the sound of snakes, i.e., the Batesian mimicry hypothesis. We also note however that our results also agree with another hypothesis, suggesting that mechanisms underlying the production and perception of hisses are conserved across vertebrates. Further research is needed to disentangle these two hypotheses. Significance statement: Mimicry is a fascinating illustration of the principles of evolution in communication. In the case of Batesian mimicry, species evolve to resemble other species as a mean of deterring harmful receivers. While visual mimicry has been thoroughly investigated across a wide range of species, vocal mimicry remains less studied. In the present study, we compared the acoustic similarity of the hissing sound produced by female blue tits, a cavity-nesting species, to the hisses of three snake species. Then, we exposed mice, a model of a possible cavity competitor, to bird and snake hisses. We showed that snake and blue tit hisses are acoustically similar and provoke comparable anxiety behaviors in mice. These results are compatible with the hypothesis that blue tits utilize an innate fear response to hisses in mammals, a result that may explain why blue tit hisses have been linked to increased survival by other authors. Furthermore, the results also suggest a conserved function of, and response to, hiss vocalizations across vertebrates. [ABSTRACT FROM AUTHOR]