We analysed genetic relatedness through DNA-fingerprinting in 38 two-chick
families of Chinstrap Penguins Pygoscelis antarctica in the Vapour Col colo
ny on Deception Island, Antarctica. Band-sharing coefficients between males
and chicks in their nests, females and chicks in their nests and brood mat
es were very close to 0.50 and were not significantly different. Presumably
unrelated pair mates showed much lower band-sharing coefficients (0.12), w
hich differed significantly from those between putative parents and their c
hicks and between presumed siblings. No case of extra-pair paternity was de
tected according to the presence of novel bands or to band-sharing coeffici
ents. Monogamy in the study population is not only social but also genetic.