Print PageMule deer (Odocoileus hemionus) populations have increased over the last few decades within the human-inhabited area of the Rocky Mountain Biological Laboratory (“RMBL town site”) in Colorado. Our student-led team hypothesized that deer have become more common during summer months because they avoid coyotes (Canis latrans), which prey on fawns, and coyotes avoid humans. According to scientific literature, even though coyotes do not eat plants, they can incidentally affect them by killing, frightening or altering the behavior of deer. This could represent a trophic cascade which ultimately influences browsing of local plants. To explore whether deer are more common in the RMBL town site we repeatedly scanned for deer at known observation points inside and outside the town site between June and July 2010. To explore whether coyotes avoided the town site during summer, we collected coyote scat along transects both within and outside the town site. Initial sampling during the early summer indicated that coyotes used the town site during winter, when only few people are present. However, cattle activity significantly destroyed coyote sign before we could repeat the sample later on in the summer. To assess whether greater deer activity translates into greater herbivory we established permanent plant transects at sites used to sample deer activity. To see whether deer responded to presence of coyotes, we added coyote urine to some meadows within the RMBL town site, with other paired meadows as controls.
Results/Conclusions
Our results indicated that deer (especially does and fawns) are seen significantly more often in the town site. As of this point we cannot determine whether coyotes avoided the town site during summer, although sightings there are very uncommon. Plant transects demonstrated that browsing rate (adjusted for overall species preferences) increased with deer activity, although not significantly so. Coyote urine addition caused no clear shift in deer vigilance or foraging behavior, perhaps because deer habituated to scent when other cues of predation risk were absent. However, deer spent more time feeding at sites that were near the cover of willows or aspen forest. Higher density of deer in the RMBL town site might be due to absence of coyotes, but at this point we cannot exclude other possibilities, such as availability of good fawning habitat within the town site, or absence of cattle grazing there. This project is ongoing, and future students who join it have great challenges to look forward to.
