Weather explains differences in sagebrush-obligate songbird nest success under various grazing regimes

Livestock grazing occurs worldwide, spanning over 25% of land globally, and effective conservation of biodiversity relies upon understanding the interactions of agricultural management practices and increasingly variable weather associated with climate change. We evaluated precipitation and temperature and the daily nest survival rates of two species of sagebrush-obligate songbirds, Brewer’s sparrow (Spizella breweri) and sagebrush sparrow (Artemisiospiza nevadensis) under dormant season grazing, rotational grazing and a non-grazed control. Precipitation and temperature were quantified as daily time-varying and averages across the breeding season. Both sparrow species in our study were influenced by within-year weather variation, and experienced declines in daily nest survival beyond precipitation thresholds. For sagebrush sparrows, an interaction of precipitation and temperature indicated nest survival was lowest during 5-day time frames with minimal precipitation and high temperatures. While we found moderate grazing lowered perennial grass cover, there was no support for vegetation differences associated with moderate grazing explaining daily nest survival. Our results indicate that variable weather presented a much greater threat to these birds than reductions in herbaceous cover caused by moderate grazing under the studied conditions. Management should focus on conserving extensive tracts of suitable habitat to increase songbird populations and resiliency to increasingly variable and extreme weather conditions.