Living on the edge: Predicting songbird response to management and environmental changes across an ecotone

Abstract

Effective wildlife management requires robust information regarding population status, habitat requirements, and likely responses to changing resource conditions. Single‐species management may inadequately conserve communities and result in undesired effects to non‐target species. Thus, management can benefit from understanding habitat relationships for multiple species. Pinyon pine and juniper (Pinus spp. and Juniperus spp.) are expanding into sagebrush‐dominated (Artemisia spp.) ecosystems within North America and mechanical removal of these trees is frequently conducted to restore sagebrush ecosystems and recover Greater Sage‐grouse (Centrocercus urophasianus). However, pinyon‐juniper removal effects on non‐target species are poorly understood, and changing pinyon‐juniper woodland dynamics, climate, and anthropogenic development may obscure conservation priorities. To better predict responses to changing resource conditions, evaluate non‐target effects of pinyon‐juniper removal, prioritize species for conservation, and inform species recovery within pinyon‐juniper and sagebrush ecosystems, we modeled population trends and density‐habitat relationships for four sagebrush‐associated, four pinyon‐juniper‐associated, and three generalist songbird species with respect to these ecosystems. We fit hierarchical population models to point count data collected throughout the western United States from 2008 to 2020. We found regional population changes for 10 of 11 species investigated; 6 of which increased in the highest elevation region of our study. Our models indicate pinyon‐juniper removal will benefit Brewer's Sparrow (Spizella breweri), Green‐tailed Towhee (Pipilo chlorurus), and Sage Thrasher (Oreoscoptes montanus) densities. Conversely, we predict largest negative effects of pinyon‐juniper removal for species occupying early successional pinyon‐juniper woodlands: Bewick's Wren (Thryomanes bewickii), Black‐throated Gray Warblers (Setophaga nigrescens), Gray Flycatcher (Empidonax wrightii), and Juniper Titmouse (Baeolophus ridgwayi). Our results highlight the importance of considering effects to non‐target species before implementing large‐scale habitat manipulations. Our modeling framework can help prioritize species and regions for conservation action, infer effects of management interventions and a changing environment on wildlife, and help land managers balance habitat requirements across ecosystems.

Impacts of umbrella species management on non‐target species

“…Our results demonstrate lower abundance and fledgling production in removal areas, highlighting the importance of scattered trees for them (Figures 3 and 5). To complicate matters, towhees have mixed population trajectories across their range, with decreases in some areas and increases in others (Sauer et al., 2019; Van Lanen et al., 2023b). Recent large‐scale mapping shows that conifer encroachment has likely increased towhee habitat across broad swaths of their range while infill has dramatically decreased the suitability of historically open conifer forests (Dobbs et al., 2020; Filippelli et al., 2020).…”

“…Conifer removal is a restoration practice that has the potential to provide significant benefits for declining sagebrush‐associated species with limited harm to woodland‐associated species (Tack et al., 2023; Van Lanen et al., 2023b). Our demographic analysis provides confirmation of the assumed benefits for sagebrush songbirds and allows decision‐makers to quantify the impact of removal treatments on populations.…”