PS 45-196 - Enhancing Avian Habitat Quality with Heterogeneity-based Grazing Strategies

Abstract: Rangelands comprise a large portion of global land cover and as a result management in these landscapes has significant consequences for the conservation of biodiversity. Current utilitarian management regimes of many rangelands reduce variation in vegetation structure and composition that can benefit biodiversity. More specifically, the homogenization of rangeland ecosystems has reduced avian niche diversity and contributed to rapid and widespread grassland bird declines. Recoupling historic fire regimes with grazing can restore variation in vegetation structure and composition leading to more diverse avian communities. However, regions with a cultural aversion to fire require innovative grazing strategies that utilize existing infrastructure to restore heterogeneity. We examined the impacts of one conventional and two heterogeneity-based grazing strategies on territory size, a proxy of territory quality, of the Western Meadowlark (Sturnella neglecta). Smaller territories should indicate higher quality habitat because adults spend less time away from the nest either defending territory boundaries or foraging, resulting in higher nest survival. We delineated territories from mid-May to early June within 12 pastures managed with either a conventional, season-long continuous or a heterogeneity-based patch-burn grazing or modified twice-over rest-rotation grazing strategy. We characterized the vegetation composition and structure along three 100-meter transects within 17 territories. Territory sizes tended to be larger with conventional grazing, but not significantly different between grazing strategies (p > 0.05). However, the conventional grazing strategy showed more variation in territory size than heterogeneity-based grazing strategies. While vegetation composition did not directly impact territory size, more variability in territory size may indicate a patchy distribution of high-quality habitat with conventional grazing strategies. Furthermore, structural equation modeling revealed that vegetation structural components were the most important predictors of territory size. Vegetation density and bare ground both indirectly impacted territory size by altering litter abundance and litter depth, respectively. Litter abundance and litter depth were the only vegetation characteristics to directly impact territory size and were approximately 3% stronger than second-order characteristics. More abundant litter increased territory size whereas deeper litter reduced territory size. These findings demonstrate that litter alters avian habitat quality in complex ways and may be more important than other structural components when promoting high-quality avian habitat. Deep but patchy litter within territories may allow ground-nesting grassland birds opportunities to conceal their nests without sacrificing foraging efficiency. Understanding the complex interaction between grazing strategies, vegetation structure, and habitat quality will promote more informed decisions when incorporating avian conservation into rangeland management.