Dads on Duty: First account of nest sitting in Barnacle ganders

In most Anseriformes (ducks, geese and swans) only females are known to incu-
bate. 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 iden-
tifying 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: protec-
tion against aerial predators, thermal control of nest temperature and protection
against intraspecific brood parasitism. At this time, we cannot confirm the func-
tion 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 autum-
nalis.