Papers by Benjamin Pitcher
Proceedings of the National Academy of Sciences of the United States of America, Jan 8, 2015
Journal of Zoology, 2014
We conducted a study of the male rut vocalizations (groans) of two closely related species, Persi... more We conducted a study of the male rut vocalizations (groans) of two closely related species, Persian and European fallow deer. Persian fallow deer are endangered, restricted to Iran and Israel, and their rut vocalizations have never been studied. By contrast, European fallow deer are one of the most common deer species in the world, and have been the subject of numerous detailed studies. Persian bucks are approximately 16% larger than European bucks, and this can have important implications for vocalizations. Persian bucks were recorded in Israel, and European bucks were recorded in the UK and Ireland. We measured temporal, fundamental frequency-related and formant-related parameters of groans and determined which acoustic parameters differed among species and populations. The comparisons revealed important structural similarities and differences, with the differences more strongly related to temporal than spectral vocal parameters. Persian buck groans were relatively long, pulsed calls of almost 1-s duration, with low fundamental frequencies, and relatively weak formant modulation. European buck groans were much shorter (0.38 s), but with similarly low fundamental frequencies and clearer formant modulation. We found some minor differences in the formant frequencies (F4 and F5) of calls of the two European fallow populations. Given the length of time since Persian and European fallow deer diverged, and that both their mitochondrial and nuclear genomes are very different, it is notable that the structure of their groans is still so similar. Our findings suggest that the factors influencing the evolution of these vocalizations (e.g. sensory system characteristics, environment and mate choice) have probably been similar for both species.
Vertebrates that eavesdrop on heterospecific alarm calls must distinguish alarms from sounds that... more Vertebrates that eavesdrop on heterospecific alarm calls must distinguish alarms from sounds that can safely be ignored, but the mechanisms for identifying heterospecific alarm calls are poorly understood. While vertebrates learn to identify heterospecific alarms through experience, some can also respond to unfamiliar alarm calls that are acoustically similar to conspecific alarm calls. We used synthetic calls to test the role of specific acoustic properties in alarm call identification by superb fairy-wrens, Malurus cyaneus. Individuals fled more often in response to synthetic calls with peak frequencies closer to those of conspecific calls, even if other acoustic features were dissimilar to that of fairy-wren calls. Further, they then spent more time in cover following calls that had both peak frequencies and frequency modulation rates closer to natural fairy-wren means. Thus, fairy-wrens use similarity in specific acoustic properties to identify alarms and adjust a two-stage antipredator response. Our study reveals how birds respond to heterospecific alarm calls without experience, and, together with previous work using playback of natural calls, shows that both acoustic similarity and learning are important for interspecific eavesdropping. More generally, this study reconciles contrasting views on the importance of alarm signal structure and learning in recognition of heterospecific alarms.
Animal Behaviour, Jan 1, 2012
Behavioral Ecology, Jan 1, 2007
Individuals are likely to benefit from responding to the alarm signals of other species with simi... more Individuals are likely to benefit from responding to the alarm signals of other species with similar predators, and mutual interspecific responses to aerial (hawk) alarms are thought to be common in birds, in part because similarity in alarm call structure among species might facilitate detection or interpretation. However, there has been no test of whether interspecific responses to aerial alarm calls can involve mutual responses between species and only incomplete tests of the response of any species to such heterospecific alarms. We describe the aerial alarm calls of white-browed scrubwrens (Sericornis frontalis) and superb fairy-wrens (Malurus cyaneus) and use a playback experiment to test for mutual responses to each other's aerial alarm calls. The 2 species occur in similar habitats and can co-occur in mixed-species flocks during the nonbreeding season. The aerial alarm calls of both species are high pitched (7 kHz) and rapidly frequency-modulated calls but are distinct in frequency measures and only the scrubwren's call had 2 parallel sounds. Both species fled to cover after playback of either their own or the other species' alarm calls but never to control sounds. The response to either species' alarm was almost invariant in both species in an experiment at high natural amplitude, but there was a slightly lower response to heterospecific compared with conspecific alarms when playbacks were at the mean natural amplitude. Our results demonstrate, after at least 50 years of interest in the subject, that there can be mutual responses to aerial alarm calls between species.
Animal Behaviour, Jan 1, 2007
… of the Royal …, Jan 1, 2009
Alarm calls given by other species potentially provide a network of information about danger, but... more Alarm calls given by other species potentially provide a network of information about danger, but little is known about the role of acoustic similarity compared with learning in recognition of heterospecific calls. In particular, the aerial 'hawk' alarm calls of passerines provide a textbook example of signal design because many species have converged on a design that thwarts eavesdropping by hawks, and call similarity might therefore allow recognition. We measured the response of fairy-wrens (Malurus cyaneus) to playback of acoustically similar scrubwren (Sericornis frontalis) aerial alarm calls. First, if call similarity prompts escape independent of learning, then fairy-wrens should flee to playback of scrubwren calls outside their geographical range. However, fairy-wrens fled only in sympatry. Second, if call similarity is necessary for learning heterospecific calls, then fairy-wrens should not respond to sympatric species with different calls. We found, on the contrary, that fairy-wrens fled to the very different aerial alarm calls of a honeyeater (Phylidonyris novaehollandiae). Furthermore, response to the honeyeater depended on the specific structure of the call, not acoustic similarity. Overall, call similarity was neither sufficient nor necessary for interspecific recognition, implying learning is essential in the complex task of sifting the acoustic world for cues about danger.
Behavioral Ecology, Jan 1, 2009
Alarm calls potentially provide information about predators to heterospecifics, but little is kno... more Alarm calls potentially provide information about predators to heterospecifics, but little is known about patterns of eavesdropping among species. Many cases of eavesdropping in birds and mammals involve social species in mixed-species groups, but this is not always true and the reliability of information may also be critical. We used a playback experiment and observations of natural alarm calling to test for understanding of aerial ''hawk'' alarms among 3 species of passerine and assess call reliability. Superb fairy-wrens and white-browed scrubwrens are ecologically similar and can share mixed-species flocks, whereas New Holland honeyeaters are ecologically distinct and do not flock with the other species. Fairy-wrens and scrubwrens fled to cover to each other's alarm calls, but they also both fled to honeyeater alarms. Honeyeaters fled to scrubwren but usually not fairy-wren alarms. The pattern of heterospecific responses appears related to call reliability from each species' perspective. Honeyeaters called only to predators of all 3 species and so provided reliable information to all. From a honeyeater's perspective, fairy-wrens were least reliable, as they gave 52% of their calls to nonpredators, whereas scrubwrens gave only 18% to nonpredators. However, from a scrubwren's perspective, fairy-wrens were largely reliable because most calls to nonpredators were to red wattlebirds, which pose a physical threat to fairy-wrens and scrubwrens but not honeyeaters. We conclude that there can be mutual responses to alarm calls between ecologically distinct species, that responses can be symmetrical or asymmetrical between species, and that call reliability appears to affect response.
Animal Behaviour, Jan 1, 2009
Australian sea lion environmental constraint individual recognition maternal behaviour Neophoca c... more Australian sea lion environmental constraint individual recognition maternal behaviour Neophoca cinerea pinniped As in all otariids, Australian sea lion, Neophoca cinerea, females alternate foraging trips at sea with suckling periods ashore, and each time they return, mothers and pups have to find each other among individuals at the colony. The need for a finely tuned mechanism of individual recognition is exacerbated by their habit of changing the suckling location. Using playback experiments with modified calls, we investigated the acoustic parameters involved in the discrimination of the mother by pups. The signature efficiency was also tested in the three environments in which reunions at the study site occur by performing propagation tests. Pups paid great attention to both amplitude and frequency modulations, and to the exact frequency values of the call to identify their mother. When severe modifications of AM and FM patterns were made to mothers' calls pups no longer responded to them. This may have arisen because the calls fell outside the natural species range. The energy spectrum, even though highly individualized, was not important for individual recognition. Propagation tests revealed that one particular environment was extremely harsh and did not allow accurate transfer of the individual signature components whatever the distance. In two other environments, AM was only reliable to a distance of 16 m, but both FM and frequency spectrum could be transmitted with limited degradation over 32 m. The different environments greatly influenced the efficiency of the individual identification process. Accordingly, the area in which mother-pup reunions occur is an important factor in the success of individual recognition. Ó
Naturwissenschaften, Jan 1, 2009
In pinnipeds, maternal care strategies and colony density may influence a species' individual rec... more In pinnipeds, maternal care strategies and colony density may influence a species' individual recognition system. We examined the onset of vocal recognition of mothers by Australian sea lion pups (Neophoca cinerea). At 2 months of age, pups responded significantly more to the calls of their own mothers than alien female calls demonstrating a finely tuned recognition system. However, newborn pups did not respond differentially to the calls of their mother from alien female calls suggesting that vocal recognition had not yet developed or is not yet expressed. These findings are in stark contrast to other otariid species where pups learn their mother's voice before their first separation. Variance in colony density, pup movements, and natal site fidelity may have reduced selective pressures on call recognition in young sea lions, or alternatively, another sensory system may be used for recognition in the early stage of life.
PloS one, Jan 1, 2010
Background: In many gregarious mammals, mothers and offspring have developed the abilities to rec... more Background: In many gregarious mammals, mothers and offspring have developed the abilities to recognise each other using acoustic signals. Such capacity may develop at different rates after birth/parturition, varying between species and between the participants, i.e., mothers and young. Differences in selective pressures between species, and between mothers and offspring, are likely to drive the timing of the onset of mother-young recognition. We tested the ability of Australian sea lion mothers to identify their offspring by vocalisation, and examined the onset of this behaviour in these females. We hypothesise that a rapid onset of recognition may reflect an adaptation to a colonial lifestyle.
Ethology 116 (2010) 704-712 ª
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Papers by Benjamin Pitcher