The frequency of vocal mimicry associated with danger varies due to proximity to nest and nesting stage in apasserine bird

摘要

Several species of birds vocally imitate sounds associated with danger. Two anecdotal studies suggest that such 'danger mimicry' increases during nesting, but such a relationship has not been quantitatively demonstrated. Sri Lanka drongos (Dicrurus paradiseus lophorhinus) are known to imitate predators and other species' mobbing and alarm calls in alarm contexts. Here we investigated whether drongos vary their production of danger mimicry in different nesting stages (building, incubation, nests withhatchlings, fledglings still outside of mixed-species flocks), and when foraging away from young in mixed-species flocks. We recorded drongos over two breeding seasons at 14 different nesting trees, used year-after-year. We found that of all the types ofdanger mimicry, imitation of predators was the most common and exclusive to drongos that had young offspring. Such predator mimicry was observed at a higher rate during the hatchling and fledgling stages compared to incubation or flocks. Danger mimicrydid not, however, increase during this stage in isolation: drongo species-specific alarm calls also increased, and the close connection between these two types of calls did not appear to change. Although it is possible that the association between dangermimicry and species-specific alarm calls could help young birds learn sounds associated with danger, the performance of this behaviour does not seem exclusive enough to interactions between adult drongos and their offspring to meet functional definitions of teaching.