Eavesdropping in solitary large carnivores: Black bears advance and vocalize toward cougar playbacks
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Large carnivore behavioral responses to the cues of their competitors are rarely observed, but may mediate competition between these top predators. Playback experiments, currently limited to interactions involving group-living large carnivores, demonstrate that attending to cues indicative of the immediate presence of heterospecific competitors plays a substantial role in influencing competition among these species. Group-living species vocalize regularly to signal to one another, and competitors can readily “eavesdrop” on these acoustic cues. Solitary large carnivores also vocalize to conspecifics, but much less frequently, reducing the ease with which heterospecific competitors can eavesdrop. Eavesdropping could nonetheless play a substantive role in mediating competition among solitary large carnivores if the benefits of responding to the acoustic cues of heterospecific competitors (reducing risk or locating resources) are sufficiently large. Behavioral interactions between solitary large carnivore species are almost never observed, and there have been no experimental tests of their reactions to cues indicative of the immediate presence of other solitary large carnivores. We used an automated playback system to test the responses of a solitary large carnivore (black bear, Ursus americanus) to vocalizations of their similarly solitary competitor (cougar, Puma concolor), presenting both cougar and control vocalizations to free-living bears foraging along shorelines in British Columbia, Canada. Both mothers with cubs and solitary bears were significantly more likely to advance and vocalize toward cougar than control playbacks, mothers producing one or both of two distinct vocalizations and solitary bears producing just one. Cougars could either represent a potential risk to bears (particularly cubs), or a source of resources, as bears are known to regularly scavenge cougar kills. Our results are consistent with bears eavesdropping on cougars for both these reasons. As with group-living species, eavesdropping may be common among solitary large carnivores, and may be an important driver of competition between these species.