Stimulus features of chicks and other factors evoking parental protective behaviour in ring-billed gulls

We examined the role of certain stimuli in parental approach and protection of ‘straying’ chicks by noting the response of ring-billed gulls, Larus delawarensis, to different stimuli placed within their territories. Playback of chick calls and presentation of surgically devocallzed chickes each elicited and oriented parental approach and protective behaviour, although a combination of the two was more effective. Other factors affecting a parent's reaction included the parent's reproductive state whether other offspring were present, the chick's location, and the chick'ssize relative to the parent's own chicks. These response tendencies should increase a gull's probability of responding selectively toward its own chicks before it can individually recognize them, while rejecting foreign chicks.