Sex-specific foraging of an apex predator puts females at risk of human-wildlife conflict

Urbanisation and anthropogenic alteration of ecosystems has led to
conflict between humans and wildlife. Such conflict is often observed in
apex predators. Although human-wildlife conflict has been extensively
studied, male/female differences in behaviour are rarely considered. We
investigated male/female differences in foraging behaviour of the
predatory/scavenging brown skua Catharacta antarctica lonnbergi breeding
on a New Zealand island nature reserve in proximity to farmland. These
skuas are subject to culling, when perceived as a threat to livestock. As
part of a long-term ecological study, we used high-resolution Global
Positioning System (GPS) devices to characterise the space-use of foraging
brown skuas. We also analysed stable isotopes of carbon (δ13C) and
nitrogen (δ15N) from modern and archived blood samples to investigate
possible changes in diet over the past ~30 years. Analysis of 100 GPS
tracks collected from 2014-16 demonstrated that males and females
consistently visited different habitats. Males spent most of their time
close to their breeding territory on the island nature reserve and females
frequently visited a farmed island approximately two kilometres away.
Consistent with this finding, we show that male and female skuas also
differed markedly in their diets: males specialised on burrow-nesting
white-faced storm petrels Pelagodroma marina (80%) with only a small
proportion of sheep remains Ovis aries (<6%) contributing to their
diet. In contrast, female diet comprised 27% white-faced storm petrels,
other seabirds (18%), and a relatively large proportion of sheep remains
(47%). Further, our data (186 blood samples from 122 individuals) show
that this male / female difference in diet has persisted at least since
1987. Because females fed disproportionally on sheep remains, they may be
more vulnerable to being culled by farmers. Importantly, our case study
suggests that intersexual differences in diet and foraging patterns can
have major implications for the reproduction and survival of apex
predators that interact with farming. We strongly suggest that intersexual
differences in behaviour should be considered when investigating
human-wildlife conflicts.