The effects of cattle grazing on bird diversity at Craters of the Moon National Monument and Preserve

Background/Question/Methods

Cattle grazing has the potential to negatively influence avian habitat, and our main research focus was to determine if cattle grazing in aspen stands affected avian species richness, diversity, and evenness. Additionally, we assessed the impact of bird diversity before and after cattle grazing. In the summer of 2015, we assessed bird diversity in the ungrazed aspen stands at Craters of the Moon National Monument and in grazed stands at Lava Lake Land & Livestock Ranch in southeastern Idaho. We conducted point count bird surveys in three different sites: two were ungrazed sites and one was a grazed study site.  Of the ungrazed sites, Little Cottonwood had 6 plots and Leech Creek had 10 plots. The grazed site, Big Cottonwood, had 9 plots. Each plot was surveyed three different times throughout the summer between sunrise and 10:00 a.m. and we followed the BBird Protocol for our survey methods. Species richness, diversity (using the Shannon-Wiener Diversity Index (H)) and evenness (E_H) were measured for all sites.

Results/Conclusions

The first research question assessed species richness between ungrazed and grazed sites. Ungrazed sites species richness averaged 9 (range of 6-12), the species diversity measure (H) was 2.06 (SD = 0.16), and the average E_H was 0.94 (SD = 0.03). Grazed site species richness averaged 7.8 (range of 4 -12), the species diversity index (H) was 1.86 (SD = 0.29), and the average E_H was 0.94 (SD = 0.02). There were fewer species in the grazed site compared to the ungrazed site. The ungrazed site was more diverse in terms of bird species and a higher evenness was higher. The second question was to determine bird diversity before and after cattle arrival in Big Cottonwood. Species richness before cattle arrival averaged at 8.8 (range of 5 -12), H= 2.00 (SD = 0.29), and had an E_H of 0.94 (SD = 0.02). After cattle arrival species richness averaged at 7.3 (range of 4 -12), H = 1.86 (SD = 0.063), average E_H of 0.95 (SD = 0.014). Species richness decreased by ~17% with the arrival of cattle. Our results suggest that grazing negatively influenced bird diversity but we studied a small number of study sites surveyed in a single year. If our results are replicated at multiple sites in the future, ranch managers in southeastern Idaho could use these types of studies for future management plans of cattle grazing if they are managing for bird diversity.