Large-scale fence modifications increase nest survival in sage-grouse

Abstract

Livestock grazing is the most common land-use practice in aridland ecosystems of the American West. Widespread and long-term declines of greater sage-grouse (Centrocercus urophasianus), an umbrella species for other sagebrush-associated vertebrates, has challenged land managers to find solutions to help bolster populations. Livestock grazing infrastructure (e.g., fences) among western rangelands are one potential factor impacting sage-grouse populations as nest survival – a key demographic rate that influences population size – can be 4x higher when placed >100 m away from the nearest fence. We implemented the first-ever long-term (8 years) and large-scale (70 km in length) management action designed to evaluate changes in nest survival related to fence modifications in the Centennial Valley of Montana, USA. Fence modifications included perch deterrents placed atop fence posts to reduce perching by avian nest predators. Additionally, the bottom fence wire was raised to 45 cm from the ground to reduce the funneling of mammalian predators along fences who are in search of carcasses from collisions and/or nests placed near fences. Using a Bayesian statistical framework, we found that fence modifications increased 28-day nest survival within 100 m of mitigated fences by an average of 10.6 % (85 % CRI: 3.7–24.9 %). The difference in survival between fence types was most pronounced for modified fences in low elevations, while modified fences resulted in higher survival rates throughout the nesting season. Our findings suggest that modifying fences designed to reduce the search efficiency of sage-grouse nest predators appear to benefit nest survival in sage-grouse. The highlighted fence modification technique offers practitioners a tool to advance grazing systems that reduce the impacts of grazing infrastructure on greater sage-grouse.