Elk winter foraging at fine scale in Yellowstone National Park

DANIEL, F.; MORALES, J. M.; BOYCE, M. S.

Oecologia

Springer

Año: 2005 vol. 145 p. 334 - 342

0029-8549

The link between landscape properties and foraging decisions by herbivores remains unclear, but such knowledge is central to the understanding of plant? herbivore dynamics. Our goal was to determine whether fine-scale foraging paths of free-ranging elk (Cervus canadensis) respond to spatial structure of habitats in Yellowstone National Park. During winter 2002 we gathered elk-foraging information by following snow tracks in open habitats located on hillsides and flat ter- rain. The 21 snow paths surveyed were comprised on average of 15 discrete snow craters connected to each other by relatively straight-line movements. Our analy- ses revealed two levels of selection: elk chose where to dig, and how much search effort to allocate at digging sites based on habitat characteristics. On hillsides, elk preferentially dug in areas of greater biomass of grasses and forbs, and simply walked through poorer sites without digging. Individuals also searched more inten- sively, creating larger craters, where food biomass was higher. On flat terrain, crater size decreased with snow depth and increased with snow density. Correlated random walk models usually were adequate to charac- terize elk movement on flat terrain, but not on hillsides. First, as the number of movements between local for- aging areas increased, elk displacements on hillsides became shorter than expected from random patternsThis trend on hillsides was strongly influenced by in- terindividual variation in movement behavior. Second, elk tended to forage perpendicularly to aspect, resulting in horizontal displacements. Our study demonstrates that free-ranging elk adjust their foraging to fine-scale habitat structure.