Scheiber I.B.R, Slettenhaar A.J., Loonen M.J.J.E & de Jong M.E. (2025) Dads on duty: First account of nest sitting in Barnacle ganders. ARDEA 113 (1): 21-21

In most Anseriformes (ducks, geese and swans) only females are known to incubate. Here we describe incidents of male nest sitting in Barnacle Geese Branta leucopsis as a form of paternal care. Based on pictures from wildlife cameras, we identified males sitting on their nests when their mates took incubation recesses. Wildlife cameras were placed at nests of which either the male or female was fitted with a GPS neck collar in the year prior, which aided with identifying individual birds on the nest. To attach transmitters, some geese were caught while defending their nests, thus we may have unintentionally selected bolder males as they defended their nests more aggressively and were easier to catch. Nest sitting occurred relatively frequently, i.e. in 6 out of 15 individuals. Our results show that males with collars were more likely to nest sit than males without a collar. We discuss several possible functions of this behaviour: protection against aerial predators, thermal control of nest temperature and protection against intraspecific brood parasitism. At this time, we cannot confirm the function of this behaviour, as the chances of successful hatching were not increased in broods with nest-sitting males, and we lack the necessary sample size for more in depth analyses. Lastly, we argue that ‘male incubation’ is misleading in the waterfowl literature, as it is truly justified for only two species, the Black Swan Cygnus atratus and Black-Bellied Whistling Duck Dendrocygna autumnalis.