Experimental reduction of a primary nest predator fails to decrease nest predation rates of sagebrush songbirds

Predator removal comprises one management strategy to increase the reproductive success of a prey species of concern, particularly within human-altered landscapes. The efficacy of such an approach, however, depends partly on the extent to which predation risk is additive or compensatory, which remains unknown for many systems. We experimentally reduced the local abundance of deer mice (Peromyscus maniculatus), a primary nest predator of three sagebrush-obligate songbirds (Brewer's Sparrow [Spizella breweri], Sagebrush Sparrow [Artemisiospiza nevadensis], and Sage Thrasher [Oreoscoptus montanus]) during May ̶ August 2019 in western Wyoming, USA to assess whether nest predation risk was additive or compensatory and whether nest predator removal could comprise a potentially effective management tool. Deer mouse removal did not affect the daily nest survival of songbirds between experimental and control plots, despite a reduction of 68 ̶ 85% in deer mouse abundance within treatment areas. Nest predation in this system therefore likely operated in a compensatory way, in which deer mice that escaped removal, new immigrants, or other species of nest predator maintained similar levels of nest predation risk regardless of the prevalence of a primary predator. We caution that predator removal may not be an effective management tool in systems that lack barriers to predator immigration or have several alternative species of predators, even when a single species typically is responsible for the majority of predation events.

捕食者移除是提升受关注猎物种群繁殖成功率的一类管理策略，在受人类活动干扰的景观中尤为如此。然而，该方法的有效性在一定程度上取决于捕食风险的累加性或补偿性程度，而这一问题在多数生态系统中仍未明确。为评估巢捕食风险属于累加性还是补偿性，以及移除巢捕食者是否可作为潜在有效的管理工具，本研究于2019年5月至8月在美国怀俄明州西部开展实验，降低了当地鹿鼠（Peromyscus maniculatus）的种群丰度——鹿鼠是三种依赖灌丛鸣禽的主要巢捕食者，这三种鸣禽分别为布氏麻雀（Spizella breweri）、艾草雀（Artemisiospiza nevadensis）以及艾草嘲鸫（Oreoscoptus montanus）。尽管处理样地内鹿鼠的种群丰度降低了68%至85%，但移除鹿鼠并未对实验样地与对照样地鸣禽的单日巢存活率产生影响。因此，本研究系统中的巢捕食过程大概率以补偿性模式进行：即便主要捕食者的种群占比下降，逃逸的鹿鼠、新迁入的个体或是其他巢捕食者物种仍能维持相近的巢捕食风险水平。本研究提醒，在捕食者迁入无阻碍或存在多种替代捕食者物种的生态系统中，即便某一物种通常承担了大部分捕食事件，移除捕食者也未必是有效的管理工具。