Abstract
Habitat selection by animals is influenced by and mitigates the effects of predation and environmental extremes. For birds, nest site selection is crucial to offspring production because nests are exposed to extreme weather and predation pressure. Predators that forage using olfaction often dominate nest predator communities; therefore, factors that influence olfactory detection (e.g., airflow and weather variables, including turbulence and moisture) should influence nest site selection and survival. However, few studies have assessed the importance of olfactory cover for habitat selection and survival. We assessed whether ground‐nesting birds select nest sites based on visual and/or olfactory cover. Additionally, we assessed the importance of visual cover and airflow and weather variables associated with olfactory cover in influencing nest survival. In managed grasslands in Oklahoma, USA, we monitored nests of Northern Bobwhite (Colinus virginianus), Eastern Meadowlark (Sturnella magna), and Grasshopper Sparrow (Ammodramus savannarum) during 2015 and 2016. To assess nest site selection, we compared cover variables between nests and random points. To assess factors influencing nest survival, we used visual cover and olfactory‐related measurements (i.e., airflow and weather variables) to model daily nest survival. For nest site selection, nest sites had greater overhead visual cover than random points, but no other significant differences were found. Weather variables hypothesized to influence olfactory detection, specifically precipitation and relative humidity, were the best predictors of and were positively related to daily nest survival. Selection for overhead cover likely contributed to mitigation of thermal extremes and possibly reduced detectability of nests. For daily nest survival, we hypothesize that major nest predators focused on prey other than the monitored species’ nests during high moisture conditions, thus increasing nest survival on these days. Our study highlights how mechanistic approaches to studying cover informs which dimensions are perceived and selected by animals and which dimensions confer fitness‐related benefits.
Highlights
Animal habitat selection has major implications for survival, reproductive success, fitness, and population-level processes, and habitat selection is strongly influenced by both environmental constraints and predation (Caro, 2005; Lima & Dill, 1990; Martin, 1993)
To assess the relative importance of visual cover, as well as airflow and weather variables associated with olfactory cover, in influencing daily nest survival probability, we evaluated 18 candidate models
We found that ground-nesting birds selected nest sites for overhead visual cover, but there was no clear evidence of selection for turbulence intensity or airflow slope, variables associated with olfactory cover
Summary
Animal habitat selection has major implications for survival, reproductive success, fitness, and population-level processes, and habitat selection is strongly influenced by both environmental constraints and predation (Caro, 2005; Lima & Dill, 1990; Martin, 1993). Because nest predator communities are often dominated by species that forage primarily using olfaction (hereafter, olfactory predators; Burghardt, 1966; Hughes, Price, & Banks, 2010; Nams, 1997; Slotnick, 2001; Threlfall, Law, & Banks, 2013), selection of nest sites that increase olfactory cover or decrease odor conspicuousness should increase nest survival and potentially reproductive success and fitness. We hypothesize that nest survival is best predicted by factors influencing olfactory cover (e.g., high turbulence, updrafts, moisture, and/or wind speed) because olfactory predators are generally the predominant nest predators in grasslands (see below; Lusk, Smith, Fuhlendorf, & Guthery, 2006; Pietz & Granfors, 2000; Renfrew & Ribic, 2003; Staller, Palmer, Carroll, Thornton, & Sisson, 2005). This study provides novel perspective on the mechanisms behind habitat selection patterns—as well as on the concealment and survival benefits provided by cover—and, useful insight for effectively managing habitat for prey species of conservation concern
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