S3 Data -

Sagebrush steppe is one of the most threatened ecosystems in North America. Adult density of songbirds within sagebrush steppe is a metric used to evaluate conservation actions. However, relying on only adult density to guide conservation may be misleading. Information on how conservation actions influence the nest density and nest survival of songbird species, in addition to adult density, are needed. We evaluated the relationships between nest density, nest survival, and adult density of Brewer’s sparrow (Spizella breweri) and vesper sparrow (Pooecetes gramineus) over 3 breeding seasons in central Montana. Our findings suggest that adult pairs of both species were often present in higher numbers than nests, and this relationship was most prominent for Brewer’s sparrows. However, our results do not support density dependence when considering nest survival. This discrepancy suggests that songbirds may not breed every year and that density dependence may be operating on nest densities within these populations differently than we examined. This study provides information on relationships between population demographics for 2 songbird species in grazed sagebrush steppe that will improve monitoring and management activities of conservation efforts.

蒿灌丛干草原（Sagebrush steppe）是北美受威胁最为严重的生态系统之一。鸣禽成鸟密度是评估保护行动的常用指标，但仅依赖成鸟密度指导保护工作可能产生误导。除成鸟密度外，还需明确保护行动如何影响鸣禽的巢密度与巢存活率。研究团队在蒙大拿州中部的3个繁殖季内，针对布氏麻雀（Brewer’s sparrow，学名Spizella breweri）与黄昏麻雀（vesper sparrow，学名Pooecetes gramineus）的巢密度、巢存活率及成鸟密度之间的关联展开了评估。研究结果显示，两种鸣禽的繁殖对个体数通常多于巢的数量，且该差异在布氏麻雀中最为显著。然而在分析巢存活率时，本研究结果并不支持密度依赖效应。这一差异表明，鸣禽可能并非每年都会繁殖，且这些种群的巢密度所受的密度依赖调控机制与本研究的观测模式存在差异。本研究针对放牧干扰下的蒿灌丛干草原中的两种鸣禽种群的统计特征关联提供了相关数据，相关成果可优化保护工作中的监测与管理活动。