PARENT-YOUNG VOCAL COMMUNICATION IN EARED GREBES

In a series of experiments, we played eared grebe (Podiceps nigricollis) and western grebe (Aechmophorus occidentalis) food calls in random order to eared grebe chicks brooded under the back-feathers of their parents. We examined the responses of chicks that were 12-23 h, 1 day, and 2-3 days old. Over the first 3 days, there was a significant increase in responsiveness (poking out the head and begging) to the parental food call. In similar experiments using the alarm call, eared grebe chicks with their heads out responded strongly to their own species' calls by ducking their heads beneath the back-feathers. Cross-fostered eared and western grebe chicks rarely responded to food calls of their own species, but responded vigorously to their foster species' calls. On the other hand, a cross-fostered eared grebe chick showed strong responses to the alarm calls of its own species, even though its foster parents were not using that type of call. This chick had not learned to respond to its foster species' alarms. Cross-fostered western grebe chicks responded to the alarms of both species, even though they were unlikely to have heard their own species' calls. Whether their alarm responses to both species was a manifestation of incomplete learning or of an absence of species specificity unaffected by early experiences remains to be determined. If learning was involved, it appeared to occur at a slower rate than did responses to the food calls of foster parents. The importance of learning appeared to vary considerably between the two types of calls, and the advantages of this are discussed. Although young chicks respond to the food and alarm calls from any adult of their species, playback experiments using the advertising calls of adults suggest that older grebe chicks can learn to individually identify their parents by the time they begin swimming on their own.