Effects of temperature and precipitation on grassland bird nesting success as mediated by patch size

Benjamin Zuckerberg, Christine A. Ribic, Lisa A. McCauley

Grassland birds are declining faster than any other guild of bird species across North America. Shrinking ranges and population declines have been attributed to widespread habitat loss and increasingly fragmented landscapes of agriculture and other land-use practices that are misaligned with grassland bird conservation. Concurrent with habitat loss and degradation, temperate grasslands have experienced disproportionally faster rates of climate change compared to other terrestrial biomes. Grassland bird distributions and abundances often correlate with gradients in climate, but few studies have explored the consequences of weather on the demography of multiple grassland birds inhabiting a range of grassland fragments. To do so, we modeled the effects of temperature and precipitation on nesting success rates for a dozen grassland bird species comprising 21,000 nests from 81 individual studies across North America. We found that higher amounts of precipitation in the preceding year (bioyear) were associated with higher nesting success, but wetter conditions during the active breeding season reduced nesting success. In terms of temperature, extreme cold and hot springs were associated with lower rates of nesting success. Notably, the direct and indirect influence of temperature and precipitation on nesting success was moderated by grassland patch size. The positive effects of bioyear precipitation on nesting success were strongest for birds occupying smaller grassland patches, with little effect in larger grasslands. Conversely, warmer spring temperatures reduced nesting success in small grassland patches, but increased nesting success in the larger grasslands. Mechanisms underlying these differences may be patch-size induced variation in microclimates and predator activity. While the exact cause is not clear, large grassland patches, the most common metric of grassland conservation, appears to moderate the consequences of weather on grassland bird demography and could be an effective component of climate change adaptation. This article is protected by copyright. All rights reserved.