Camera trap data: Density dependence of daily activity in three ungulate species

Daily activity in herbivores reflects a balance between finding food and
safety. The safety-in-numbers theory predicts that living in higher
population densities increases safety, which should affect this balance.
High-density populations are thus expected to show a more even
distribution of activity – i.e. spread – and higher activity levels across
the day. We tested these predictions for three ungulate species; red deer
(Cervus elaphus), roe deer (Capreolus capreolus) and wild boar (Sus
scrofa). We used camera traps to measure the level and spread of activity
across ten forest sites at the Veluwe, the Netherlands, that widely range
in ungulate density. Food availability and hunting levels were included as
covariates. Daily activity was more evenly distributed when population
density was higher for all three species. Both deer species showed
relatively more feeding activity in broad daylight and wild boar during
dusk.  Activity level increased with population density
only for wild boar. Food availability and hunting showed no correlation
with activity patterns. These findings indicate that ungulate activity is
to some degree density dependent. However, while these patterns might
result from larger populations feeling safer as the safety-in-numbers
theory states, we cannot rule out that they are the outcome of greater
intraspecific competition for food, forcing animals to forage during
suboptimal times of the day. Overall, this study demonstrates
that wild ungulates adjust their activity spread and level based on their
population size.