A seasonal pulse of ungulate neonates influences space use by carnivores
in a multi-predator, multi-prey system
Abstract
Understanding the extent to which predators engage in active search for
prey versus incidentally encountering them is important because active
search can exert a stabilizing force on prey populations by alleviating
predation pressure on low-density prey and increasing it for
high-density prey. Parturition of many large herbivores occurs during a
short and predictable temporal window in which young are highly
vulnerable to predation. Our study aims to determine how a suite of
carnivores responds to the seasonal pulse of newborn ungulates using
contemporaneous GPS locations of four species of predators and two
species of prey. We used step-selection functions to assess whether
coyotes, cougars, black bears, and bobcats actively searched for
parturient females in a low-density population of mule deer and a
high-density population of elk. We then assessed whether searching
carnivores shifted their habitat use toward areas exhibiting a high
probability of encountering neonates. None of the four carnivore species
encountered parturient mule deer more often than expected by chance
suggesting that predation of young resulted from incidental encounters.
By contrast, we determined that cougar and male bear movements
positioned them in proximity of parturient elk more often than expected
by chance which is evidence of searching behavior. Although both male
bears and cougars searched for neonates, only male bears used elk
parturition habitat in a way that dynamically tracked the phenology of
the elk birth pulse suggesting that maximizing encounters with juvenile
elk was a motivation when selecting resources. Our results support the
existence of a stabilizing mechanism to prey populations through active
search behavior by predators because carnivores in our study searched
for the high-density prey species (elk) but ignored the low-density
species (mule deer). We conclude that prey density must be high enough
to warrant active search, and that there is high interspecific and
intersexual variability in foraging strategies among large mammalian
predators and their prey.