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Department of Psychology

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https://hdl.handle.net/20.500.14078/12

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Browsing Department of Psychology by Subject "alarm calls"

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    Are the alarm calls of North American red squirrels (Tamiasciurus hudsonicus) functionally referential?
    (2009) Digweed, Shannon; Rendall, Drew
    North American red squirrels are a small-bodied and solitary-living species that faces a diversity of predators and produces two different variants of alarm calls in response to them. Recent studies have yielded conflicting interpretations of the predator-specific and functionally referential nature of these alarm call variants. We undertook a systematic set of playback experiments to quantify the responses of red squirrels to alarm calls produced by other squirrels during encounters with different predators. The experiment was designed to test a core requirement of functionally referential alarm calls, namely that different alarm call types induce distinct and functionally appropriate escape responses in listeners. Results indicated that squirrels registered and responded to alarm calls produced by others; however, their responses were not differentiated according to the type of alarm call they heard and thus did not provide evidence that the different alarm call variants hold any predator-specific, referential value. These outcomes are discussed in light of complementary work on alarm call production in red squirrels and broader aspects of this species’ life history in an effort to better understand the necessary and sufficient pressures promoting the evolution of referential call systems in animals.
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    Predator-associated vocalizations in North American red squirrels (Tamiasciurus hudsonicus): are alarm calls predator-specific?
    (2009) Digweed, Shannon; Rendall, Drew
    North American red squirrels are a small-bodied, solitary, territorial species that faces a diversity of predators. One report suggested that red squirrels produce two distinct vocalizations to aerial and ground predators: a tonal ‘seet’ and a broadband ‘bark’, respectively. This categorical mapping between alarm call variants and predator classes suggested that red squirrels might manifest a system of predator- specific, referential alarm calls. To test this hypothesis, we undertook a multi-year study of red squirrels in southern Alberta, Canada. We report details of alarm call production by red squirrels during natural predator encounters, in response to a series of predator simulation experiments, and during encounters with non-predatory species, including conspecific territorial intruders. The pattern of alarm call production was consistent across these conditions and involved two main call types, the tonal seet call and a more broadband ‘seet-bark’ call, that corresponded closely to the bark call identified previously. However, there was little evidence that call production was specific to particular predator classes. Instead, the two call types were produced together in mixed bouts to predators of all types as well as to non-predatory species and conspecific intruders. These outcomes contradict the hypothesis that alarm calls in red squirrels are referentially-specific. We suggest instead that calls might be directed primarily at the intruders themselves and function to announce their detection and possibly aid in deterring or repelling them. This possibility is consistent with a variety of other important features of the behavior and life history of red squirrels.