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.

Increasingly, human activities, including those aimed at conserving species and ecosystems (conservation activities) influence not only the survival and fitness but also the welfare of wild animals. Animal welfare relates to how an animal is experiencing its life and encompasses both its physical and mental states. While conservation biology and animal welfare science are both multi-disciplinary fields that use scientific methods to address concerns about animals, their focus and objectives sometimes appear to conflict. However, activities impacting detrimentally on the welfare of individual animals also hamper achievement of some conservation goals, and societal acceptance is imperative to the continuation of conservation activities. Thus, the best outcomes for both disciplines will be achieved through collaboration and knowledge-sharing. Despite this recognition, cross-disciplinary information-sharing and collaborative research and practice in conservation are still rare, with the exception of the zoo context. This paper summarizes key points developed by a group of conservation and animal welfare scientists discussing scientific assessment of wild animal welfare and barriers to progress. The dominant theme emerging was the need for a common language to facilitate cross-disciplinary progress in understanding and safeguarding the welfare of animals of wild species. Current conceptions of welfare implicit in conservation science, based mainly on “fitness” (physical states), need to be aligned with contemporary animal welfare science concepts which emphasize the dynamic integration of “fitness” and “feelings” (mental experiences) to holistically understand animals' welfare states. The way in which animal welfare is characterized influences the way it is evaluated and the emphasis put on different features of welfare, as well as, the importance placed on the outcomes of such evaluations and how that information is used, for example in policy development and decision-making. Salient examples from the New Zealand and Australian context are presented to illustrate. To genuinely progress our understanding and evaluation of wild animal welfare and optimize the aims of both scientific disciplines, conservation and animal welfare scientists should work together to evolve and apply a common understanding of welfare. To facilitate this, we propose the formal development of a new discipline, Conservation Welfare, integrating the expertise of scientists from both fields.

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.

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.

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.