Cattle Grazing Intensity and Duration Have Varied Effects on Songbird Nest Survival in Mixed-Grass Prairies

Abstract

Grassland bird species are declining more quickly than birds of any other biome in North America, but effects of the most widespread use of native mixed-grass prairies, livestock grazing, on nest survival of songbirds are not well understood. We used an adaptive management grazing experiment in southwestern Saskatchewan to evaluate effects of cattle grazing intensity and number of years grazed on nest survival of five songbird species in 2009 and 2010. Two 300-m² plots were located in each of 12 pastures. Three pastures were ungrazed controls, while the remaining pastures had grazing intensities ranging from 0.23 to 0.83 animal unit months (AUM) · ha−1 (very low to very high for this region) and were grazed for 2−3 or > 15 yr. Analyses were conducted using logistic exposure regression. We found few effects of grazing on nest survival. Exceptions to this pattern were that the lowest nest survival rates occurred at low-moderate grazing intensities for Sprague’s pipits (Anthus spragueii) in 2009, at low grazing intensities for chestnut-collared longspurs (Calcarius ornatus) in 2009, and at moderate grazing intensities for vesper sparrows (Pooecetes gramineus) in 2010. Increasing grazing duration lowered nest survival for Sprague’s pipits and increased nest survival for chestnut-collared longspurs in 2009. Although low or moderate grazing intensities are generally recommended to promote wildlife conservation, this may not promote productivity of all species. Nonetheless, our results suggest that in the short term, a wide range of grazing intensities is consistent with conservation of grassland songbirds.