Incubation Behavior of Emperor Geese Compared with Other Geese: Interactions of Predation, Body Size, and Energetics

Abstract

Abstract The incubation constancy of 11 female Emperor Geese (Chen canagica) was monitored electronically and behavior of both sexes was observed during incubation recesses in 1983 and 1984 at Kokechik Bay, Alaska. Average nest attentiveness of female Emperor Geese was 99.5% during 4,800 h of monitored incubation time. Recesses averaged (±SE) 13.3 ± 0.8 min, and modal recess length was 8 min (n = 107). Recess frequency was 0.54/day. This high degree of nest attentiveness exceeded that reported for any goose species. Nest attentiveness did not vary significantly through the incubation period, but increased in the last 3 days, probably in response to embryo noises and pipping. Most recesses (45%) occurred between 1200 and 1800, the warmest portion of the day. There were no significant differences in recess length at different times of day, however, and recess duration and frequency were not related to differences in daily temperature or wind speed. Females fed for only 14% of the time during their infrequent and brief recesses. Most time (43%) during recesses was spent preening and bathing. Males were alert for 49% of the time females were on recess but were present during only 56% of recesses, reflecting their relative lack of attendance during incubation. Behavior of females during recesses when males were absent did not differ significantly from when males were present. The high incubation constancy, loss of body mass during incubation (20.7%), and relatively large average clutch size (5.2) indicate that Emperor Geese arrive on nesting grounds with an extremely high level of endogenous reserves relative to other geese. Clutch size and incubation behavior also represent trade-offs in energy investment related to body size, egg size, food availability, and feeding needs during incubation. Generally, larger species or subspecies of geese depend more on endogenous reserves than do smaller forms. We believe, however, that this relationship is not satisfactorily explained just by energetic constraints related to body size because Emperor Geese were more attentive to incubation than even larger goose species. Emperor Geese usually can defend their nests from arctic foxes (Alopex lagopus) but, when on incubation recesses, are apparently less efficient in defense against avian predators than sympatric-nesting smaller geese. These smaller species are more vulnerable to foxes but more agile and effective against avian predators. The incubation constancy of geese results from an interaction of predation pressures related to body size and defense capabilities.