Dual-use habitats of <i>Contopus cooperi</i> (Olive-sided Flycatcher): Important spring stopovers for Alaskan populations coincide with shrinking areas of breeding habitat in Northern California

Abstract Despite potential conservation significance, little research to date has evaluated how different conspecific populations (migratory vs. breeding) may use the same habitat throughout the year. We evaluated such “dual-use” habitats for a long-distance, migratory passerine of conservation concern with sharp population declines range wide. We found evidence that Contopus cooperi (Olive-sided Flycatcher) migrating to Alaska in May uses the same high-elevation, open-forest habitats for stopovers in northern California that spatially correspond to high-occupancy breeding areas of local populations in June and July. We also found that availability of high-occupancy breeding habitat has shrunk and shifted to higher elevations in response to climate change. This trend has been apparently mitigated in part by the larger elevational range of the Sierra Nevada, which offers more available habitat compared to lower elevation sites in the Klamath Mountains. We recommend tests of habitat management treatments at dual-use sites for this species and others, because such efforts can potentially improve conditions and inform targeting of effective conservation actions for multiple conspecific populations during both the migratory and breeding phases of the annual cycle.