Supernormal stimulus begging calls of brood-parasitic nestlings depress
the parental care of an uncommon host
Abstract
During the nestling period, brood-parasitic birds stimulate host parents
to provide food through complex visual and auditory signals, including
emitting supernormal stimuli in the form of begging calls to increase
the feeding frequency. However, whether the begging calls of
brood-parasitic nestlings act as a universal type of supernormal
stimulus signal and their effects on less common host species still
require further research. In this study, we used playback recordings to
verify the impact of the begging calls of Common Cuckoo nestlings on the
parental care behaviour of host Barn Swallow parents. The results showed
that male Barn Swallow parents, but not female parents, reduced their
feeding frequency in response to both type of cuckoo nestling calls (the
begging calls of cuckoo nestlings reared by common/uncommon hosts).
Thus, the total feeding frequency in the two experimental groups was
significantly lower than the control group. Additionally, brood size,
temperature, and weather all affected the feeding frequency in the Barn
Swallow. This study supports the idea that the supernormal stimulus of
brood-parasitic nestling begging calls does not always work as a
universal signal; the behavioural adaptations formed by parasitic birds
in response to common hosts may lead to reduced fitness when utilising
uncommon hosts, e.g., the Barn Swallow.