Social Dominance and Reproductive Success in a Goose Flock (Anser Indicus)

Abstract

To investigate how dominance affects annual reproductive success in a permanently monogamous species, social dominance of pairs in winter was compared with various components of subsequent fledging success in a semi-captive flock of bar-headed geese (Anser indicus). Other pair characteristics (ages of mates and pairbond duration) were also analysed as they correlated with dominance and fledging success. In the two study years 1982 and 1983 the geese were provided with ad lib. food but an apparently limiting number of nest sites. - Nest search period: As future non-breeders were more often driven off nest sites than future breeders, although their frequencies of nest building behaviour were not significantly lower, apparently dominance rather than breeding propensity determined whether a pair bred. The inverse relationship with the frequency of being displaced at nest sites was stronger for dominance than for age and pairbond duration. - Incubation period: In 1982 nests were in solid boxes with only a narrow entrance. Disturbance risk was probably low, and none of the pair characteristics correlated with the number of young hatched (HS). In 1983 boxes were low-walled and open-topped, and all pair characteristics were associated with HS, dominance and female age most closely. Correlations with other parameters suggested three independent influences on HS: (1) Older male - higher dominance - more success in nest defence - fewer eggs lost or broken- higher HS, (2) older male - more nest attendance - higher HS, (3) older female - higher HS. - Young-rearing period: HS was the major determinant of variation in the number of goslings fledged per pair, while gosling survival did not significantly 'correlate with fledging success. - In an experimental competitive feeding situation females of more dominant pairs showed higher peck rates. However, peck rates were unrelated to reproductive success in this study, as food was abundant at all other times. - The importance of male dominance for parental success may be the ultimate cause of sexual dimorphism (size and aggressiveness) in geese and swans.