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November 16, 2023

FORT scientists Nicholas Van Lanen, Adrian Monroe, and Cameron Aldridge recently published population trends and density-habitat associations for 11 songbird species using summertime point count data collected throughout the Intermountain West. These maps can help managers identify areas for protection or where management activities may have undesired effects on species.

Adult Sage Thrasher waiting to deliver food to its nestlings.
The sage thrasher is considered a sagebrush obligate and is generally dependent on large patches and expanses of sagebrush steppe for successful breeding. Sagebrush habitat is currently in decline due to factors including climate change, anthropogenic development, and expansion of conifer forests.

Many wildlife populations are declining globally due to environmental changes including habitat loss and fragmentation, a changing climate, and changes in land use and management. As a result, managers tasked with maintaining healthy wildlife populations can benefit from information regarding current population trajectories and likely wildlife response to environmental change.

To address this need, we modeled population trends and density-habitat associations for 11 songbird species (Bewick’s wren, black-throated gray warbler, Brewer’s sparrow, gray flycatcher, gray vireo, green-tailed towhee, juniper titmouse, loggerhead shrike, sagebrush sparrow, sage thrasher, and Townsend’s solitaire) using summertime point count data collected throughout the Intermountain West.

We found regional population changes for 10 species. Cooler and wetter weather was associated with increases in density for five of the study species, while no species increased with warmer and drier conditions. Anthropogenic development is expected to negatively affect six of the 11 species investigated, but may benefit two species. Model results indicate pinyon-juniper removal may increase Brewer’s sparrow, green-tailed towhee, and sage thrasher densities. Conversely, pinyon-juniper removal is expected to reduce Bewick’s wren, black-throated gray warblers, gray flycatcher, and juniper titmouse densities the most.


Our study results highlight the importance of considering effects to non-target species before implementing large-scale habitat manipulations. The predicted density distribution maps (available via the associated data release) can be used by managers to assess the potential for species of interest to be affected by place-based management practices throughout the Intermountain West. 

Full citation: Van Lanen, N.J., A.P. Monroe, C.L. Aldridge. 2023. Living on the edge: Predicting songbird response to management and environmental changes at an ecological boundary. Ecology and Evolution.

Pinyon-juniper and sagebrush on Juniper Mountain, NV
A pinyon-juniper forest expanding into sagebrush habitat in Nevada. Conifer removal has become a popular management tool for restoring sagebrush habitat, but studies like this one demonstrate that its effects are species-specific. The data published here can aid managers in deciding when and where activities like conifer removal can be most beneficial (or less detrimental) to multiple species. Photo by Steve Hanser (USGS)          

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