Urban noise and its predictability moderate perceived risk associated with roads in grey squirrels

Human activity and disturbance are thought to be perceived as a source of
risk analogous to predation risk in wildlife. As such, can alter behaviour
and habitat use of foraging animals. Through increased exposure
to human disturbance, urban wildlife may face an increase in perceived
risk during food acquisition. Urban habitats also include novel resources
that could result in urban wildlife having to face distinct trade-offs
associated with foraging and patch use. To examine how a successful
invasive mammal, the eastern grey squirrel, balances risk and safety under
human disturbance, we measured giving-up densities (GUD) at artificial
food patches placed at sites subject to varying levels of urbanisation to
investigate how features associated with human disturbance might influence
feeding decisions. We found differences in GUDs between ‘safe’ and risky’
patches were reduced closer to roads under noisy conditions, suggesting
that the risk of predation is perceived by squirrels as reduced when
disturbance from human activities is highest. There was also a significant
effect of the variability in noise levels on patterns of patch
exploitation associated with roads, with the larger GUD differences
between safe and risky patches found further from roads exacerbated under
more variable noise levels, suggesting the consistency of human
disturbances also moderated squirrel risk perception while foraging close
to roads. Our results suggest that human activities can have doubled-edged
impacts on the urban landscape of fear through offering reduced risk from
predators whilst increasing foraging costs via noise disturbance.