What Cues Do Ungulates Use to Assess Predation Risk in Dense Temperate Forests?

Anti-predator responses by ungulates can be based on habitat features or on the near-imminent threat of predators.
In dense forest, cues that ungulates use to assess predation risk likely differ from half-open landscapes, as scent
relative to sight is predicted to be more important. We studied, in the Białowieża Primeval Forest (Poland), whether
perceived predation risk in red deer (Cervus elaphus) and wild boar (Sus scrofa) is related to habitat visibility or
olfactory cues of a predator. We used camera traps in two different set-ups to record undisturbed ungulate behavior
and fresh wolf (Canis lupus) scats as olfactory cue. Habitat visibility at fixed locations in deciduous old growth forest
affected neither vigilance levels nor visitation rate and cumulative visitation time of both ungulate species. However,
red deer showed a more than two-fold increase of vigilance level from 22% of the time present on control plots to
46% on experimental plots containing one wolf scat. Higher vigilance came at the expense of time spent foraging,
which decreased from 32% to 12% while exposed to the wolf scat. These behavioral changes were most pronounced
during the first week of the experiment but continuous monitoring of the plots suggested that they might last for
several weeks. Wild boar did not show behavioral responses indicating higher perceived predation risk. Visitation rate
and cumulative visitation time were not affected by the presence of a wolf scat in both ungulate species. The current
study showed that perceived predation risk in red deer and wild boar is not related to habitat visibility in a dense
forest ecosystem. However, olfactory cues of wolves affected foraging behavior of their preferred prey species red
deer. We showed that odor of wolves in an ecologically equivalent dose is sufficient to create fine-scale risk factors
for red deer.