Competition for resources and space can drive forage selection of large herbivores from the bite through the landscape scale. Animal behavior and foraging patterns are also influenced by abiotic and biotic factors. Fine-scale mechanisms of density-dependent foraging at the bite scale are likely consistent with density-dependent behavioral patterns observed at broader scales, but few studies have directly tested this assertion. Here, we tested if space use intensity, a proxy of spatiotemporal density, affects foraging mechanisms at fine spatial scales similarly to density-dependent effects observed at broader scales in caribou. We specifically assessed how behavioral choices are affected by space use intensity and environmental processes using behavioral state and forage selection data from caribou (<i>Rangifer tarandus granti</i>) observed from GPS video-camera collars using a multivariate discrete-choice modeling framework. We found that the probability of eating shrubs increased with increasing caribou space use intensity and cover of <i>Salix</i> spp. shrubs, whereas the probability of eating lichen decreased. Insects also affected fine-scale foraging behavior by reducing the overall probability of eating. Strong eastward winds mitigated the negative effects of insects and resulted in higher probabilities of eating lichen. Lastly, caribou exhibited foraging functional responses wherein their probability of selecting each food type increased as the availability (% cover) of that food increased. Space use intensity signals of fine-scale foraging were consistent with density-dependent responses observed at larger scales and with recent evidence suggesting declining reproductive rates in the same caribou population. Our results highlight the potential risks of overgrazing on sensitive forage species such as lichen. Remote investigation of the functional responses of foraging behaviors provides exciting future applications where spatial models can identify high-quality habitats for conservation.

In the springs of 2018 and 2019, 30 adult female caribou were captured and fitted with a GPS-Iridium collar integrated with a camera (VERTEX Plus Iridium V 3.0, Vectronic Aerospace GmbH, Germany; see Ehlers et al., 2021). All animal captures were conducted by the Alaska Department of Fish and Game (ADFG) and approved in accordance with ADFG animal welfare standards (IACUC Permit numbers through ADFG: 0002-2018 and 0002-2019). Video collars recorded a 9-second video every 20 minutes during daylight hours (14 – 18 hours/day) from 10 May – 10 September 2018 and 2019. The internal GPS recorded spatial locations immediately following each 9-second video recording (see Ehlers et al. 2021). We used video collars to analyze the behavior and food choices of caribou during summer. We processed data from video collars using a two-phased approach that included both community science volunteers and botanists (see Ehlers et al. 2021 for details). In 18,134 processed videos, caribou behavior was classified into six categories for our spatial analysis of behavior: eating, ruminating, traveling, stationary awake, napping, or other (e.g., drinking, licking soil for minerals, and wading; Ehlers et al., 2021). We removed 44 classified videos that were missing spatial locations due to GPS error, leaving a final sample size of 18,090 behavior-classified videos for our spatial behavior and diet analyses.