Emperor penguin mates: keeping together in the crowd

Abstract

As emperor penguins have no breeding territories, a key issue for both members of a pair is not to be separated until the egg is laid and transferred to the male. Both birds remain silent after mating and thereby reduce the risk of having the pair bond broken by unpaired birds. However, silence prevents finding each other if the pair is separated. Huddles-the key to saving energy in the cold and the long breeding fast-continuously form and break up, but not all birds are involved simultaneously. We studied the behaviour of four pairs before laying. Temperature and light intensity measurements allowed us to precisely detect the occurrence of huddling episodes and to determine the surrounding temperature. The four pairs huddled simultaneously for only 6 per cent of the time when weather conditions were harshest. Despite this asynchrony, the huddling behaviour and the resulting benefits were similar between pairs. By contrast, the huddling behaviour of mates was synchronized for 84 per cent of events. By coordinating their huddling behaviour during courtship despite the apparent confusion within a huddle and its ever-changing structure, both individuals save energy while securing their partnership.

Figure 1

Representative example of temperature and light recordings on an emperor penguin's back (female 1 on 27 April) for two consecutive huddling bouts (between dotted lines). The first episode occurs during the night and the second at the onset of the day (see text for explanations).

Figure 2

(a) Huddling bout durations from 2 to 15 May, representing the asynchrony between pairs; (b) detail showing huddling bouts recorded for the four pairs, held in common by both partners, revealed by external temperature during 6 May. Grey areas stand for civil night (black, pair 1; red, pair 2; green, pair 3; blue, pair 4).

Figure 3

Percentages of events (black bars) and time (grey bars) as a function of the number of pairs simultaneously engaged in huddling bouts and according to wind chill (top). Different letters indicate significant differences. Means±s.e.m.

Figure 4

(a) Huddling bout durations from 21 April to 14 May; (b) detail showing huddling bouts revealed by external temperature recorded for pair 1 (black, male; grey, female) during 5 May. Grey areas stand for civil night.