Impact of embryonic vocalizations on the incubation behaviour of eared grebes

Two experiment; were performed during the summers of 1991 and 1992 to determine whether embryonic vocalizations cause changes in the behaviour of adult eared grebes (Podiceps migricollis) during late incubation. In Experiment 1, a vocalizing egg was substituted in 14 nests, two days before the first egg in that nest was to begin vocalizing. Parents reduced the amount of rising and resettling and the time spent off the nest while incubating and increased the frequency of egg turning, nest building, and percent of time the 'off-duty' parent spent near the nest. Only nest builds per h in the pre-peep period differed between the sexes in Experiment 1. For Experiment 2, the incubation period was extended by two days. At that time a vocalizing egg was substituted in 15 nests. Males reduced the amount of rising and resettling, whereas there was no difference between periods for females. Males and females reduced the amount of time spent off the nest while incubating. Egg turns per h, nest builds per h, and the percent rime the off-duty parent spent near the nest increased for both sexes. No differences between males and females were detected except for egg turns per h during the peeping egg stage of Experiment 2. Parents also brought food to the nest in response to embryonic vocalizations. The behavioural changes by eared grebes during late incubation appear to be due to embryonic vocalizations. Several changes in behaviour are consistent with the care-soliciting hypothesis, such as reduction in exposure time of the embryo and possibly shortening of the incubation time of the embryo by an increased egg turning rate. Presenting food at the nest and possible acceptance of the young are further adaptive features of embryonic vocalizations.