Supernormal stimulus begging calls of brood-parasitic nestlings depress
the parental care of uncommon hosts
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 Barn Swallow parents. The results showed that
the feeding frequency in the two experimental groups (the begging calls
of cuckoo nestlings reared by common/uncommon hosts) was significantly
lower than the control group. Male Barn Swallow parents, but not female
parents, reduced their feeding frequency in response to cuckoo nestling
calls. Additionally, the number of nestlings, time of day, and weather
were all significantly correlated with the feeding frequency. This study
supports the idea that the supernormal stimulus of brood-parasitic
nestling begging calls is not a universal signal; the behavioural
adaptations formed by parasitic birds in response to common hosts may
lead to reduced fitness when utilising uncommon hosts.