University of Cape Town
Department of Zoology
Percy FitzPatrick Institute
University of Cape Town, Rondebosch
Cape Town, 7701
Abstracts (first author)
Flexible deceptive tactics of the fork-tailed drongo
Animals commonly deceive each other, but just as in Aesop’s fable ‘The boy who cried wolf’, deceptive signals cease to work when they are made too often. However, deceptive species might evade this frequency constraint by tactically varying their deceptive signal, thus maintaining their deception racket. My research investigates the behaviour of a South African bird, the Fork-tailed Drongo (Dicrurus adsimilis), which uses deceptive false alarm calls, including the mimicked alarms of other species, to scare host species and steal their food. Using a combination of observations and experiments undertaken on a wild population of individually recognisable drongos habituated to close observation, I show the benefits drongos gain from employing vocal mimicry to vary their false alarm calls. Drongos most frequently mimicked the alarm calls of a host species when using false alarms to steal food from that specific host. Furthermore, an experiment demonstrated that these mimetic alarm calls were more likely to deceive a host than the drongos own alarm calls. A second experiment showed that hosts reduced their response when the same false alarm call type was repeated, but increased their response again when the call type was changed. In natural conditions, drongos were more likely to change the type of alarm call they made when a previous false alarm call was unsuccessful and evidence indicates that this increased the likelihood drongos stole food. By tactically varying a deceptive signal, drongos exploit signals in the environment more likely to deceive a host, and potentially evade the frequency dependent constraints which typically restrict the pay-offs from deception. Results highlight that in communication systems, feedback from a receiver’s previous response provides valuable information to signallers. Furthermore, they raise questions regarding the mechanisms that enable animals to produce apparently sophisticated communication behaviour.