Fine-scale forest structure, not management regime, drives occupancy of a declining songbird, the Olive-sided Flycatcher, in the core of its range

Climate change, management legacies, pest outbreaks, and fire regimes are combining to pose a growing risk of broad-scale loss of forest cover throughout western North America. Already, habitat changes have been linked with declines in numerous bird species; understanding the relative importance of management regimes and habitat structure may be critical to conserving at-risk species. The Olive-sided Flycatcher (Contopus cooperi) is a declining songbird associated with tall, open forests in California's Sierra Nevada, the core of its breeding range, where the management regimes of the National Park Service (NPS) and U.S. Forest Service (USFS) have led to divergent forest conditions over the past century. We combined a landscape-scale passive acoustic monitoring program, the BirdNET animal sound identification algorithm, and single-season occupancy models to explore the relationships between Olive-sided Flycatchers in the Sierra Nevada and both management regimes and fine-scale forest structure. Olive-sided Flycatcher site occupancy increased as canopy cover decreased relative to mean tree diameter, which is consistent with their preference for mature, open forests. These "open forest" conditions were most prevalent on NPS-managed lands, which is consistent with the assumption that the NPS management regime is more faithful to the historical conditions that had supported a larger Olive-sided Flycatcher population than at present. Thus, the support we found for a positive association with USFS-managed lands after controlling for "open forest" suggests that other habitat features are also important. Our results suggest that conservation strategies for Olive-sided Flycatcher breeding habitat should prioritize the protection and generation of open canopies in areas with large trees, as well as the identification of other important habitat features. Prescribed fire, mechanical thinning, and a return of Indigenous forest management practices could help to restore historical forest and fire conditions beneficial to this and other species with similar habitat requirements. Fine-scale alterations to forest structure can be implemented much more rapidly and at much broader scales than the imposition of strict protected status, suggesting that there may be multiple pathways to conservation when species respond to habitat at fine spatial scales. center dot Fires are burning larger and hotter in forests across western North America, which poses a threat to forests and the wildlife that rely on them. One such species is the Olive-sided Flycatcher, which has declined by over 78% in the last 50 yr and is on pace to lose another 50% in coming decades.center dot The Sierra Nevada in California is the core of the flycatcher's range, and differing management regimes implemented by the National Park Service and the U.S. Forest Service have led to different forest conditions, which may systematically benefit this species.center dot We used passive acoustic surveys to collect thousands of hours of audio in both jurisdictions and identified Olive-sided Flycatcher songs with an artificial intelligence tool.center dot We found that differences in forest structure at the scale of several hundred meters were more important in determining where the flycatcher was found than the management regime (Park Service or Forest Service).center dot Olive-sided Flycatchers prefer forests that are relatively open yet contain relatively large-diameter (older) trees. Protecting and creating this type of habitat could help stop or even reverse declines in this species. El cambio climatico, las herencias de manejo, los brotes de plagas y los regimenes de incendios se estan combinando para plantear un creciente riesgo de perdida a gran escala de la cobertura forestal en el oeste de America del Norte. Los cambios en el habitat ya han sido vinculados con el declive de numerosas especies de aves; comprender la importancia relativa de los regimenes de manejo y de la estructura del habitat puede ser crucial para la conservacion de especies en riesgo. Contopus cooperi es un ave canora en declive asociada con bosques altos y abiertos en la Sierra Nevada de California, el nucleo de su area de reproduccion, donde los regimenes de manejo del Servicio de Parques Nacionales (NPS por sus siglas en ingles) y del Servicio Forestal de los EEUU (USFS por sus siglas en ingles) han llevado a condiciones forestales divergentes en el ultimo siglo. Combinamos un programa de monitoreo acustico pasivo a escala de paisaje, el algoritmo de identificacion de sonidos de animales de BirdNET y modelos de ocupacion de una sola temporada para explorar las relaciones entre C. cooperi en la Sierra Nevada y el regimen de manejo por un lado y la estructura fina del bosque por el otro. La ocupacion del sitio por parte de C. cooperi aumento a medida que la cobertura del dosel disminuyo en relacion con el diametro medio del arbol, lo cual es consistente con su preferencia por bosques maduros y abiertos. Estas condiciones de "bosque abierto" fueron mas prevalentes en tierras manejadas por el NPS, lo cual es consistente con la suposicion de que el regimen de manejo del NPS es mas fiel a las condiciones historicas que habian mantenido una poblacion mas grande de C. cooperi en el pasado que en la actualidad. Asi, el respaldo que encontramos para una asociacion positiva con las tierras manejadas por el USFS despues de controlar por el "bosque abierto" sugiere que otras caracteristicas del habitat tambien son importantes. Nuestros resultados sugieren que las estrategias de conservacion del habitat reproductivo de C. cooperi deben priorizar la proteccion y generacion de dosel abierto en areas con arboles grandes, asi como la identificacion de otras caracteristicas importantes del habitat. El fuego prescrito, la reduccion mecanica de la densidad y el retorno de practicas de manejo forestal Indigenas podrian ayudar a restaurar las condiciones historicas del bosque y del fuego beneficiosas para esta y otras especies con requisitos de habitat similares. Las alteraciones a pequena escala en la estructura del bosque se pueden implementar mucho mas rapidamente y a escalas mucho mas amplias que la imposicion de un estricto estatus de proteccion, lo que sugiere que pueden haber multiples vias para la conservacion cuando las especies responden al habitat a escalas espaciales pequenas.