Can the Hermit Warbler ( Setophaga occidentalis ) serve as an old-forest indicator species in the Sierra Nevada?

Efficient monitoring of the ecosystem response to climate change is crucial for conservation and restoration practices. Indicator species can serve as efficient tools for predicting the functional response of an ecosystem to climate change. Here I leverage the decades of citizen science data coupled with high-resolution spatiotemporal climate data to dissect the climate change response of hybridizing Setophaga warblers, indicator species of the temperate rainforest of North America. I found that breeding habitat temperature and precipitation significantly predicted the breeding occupancy of the northern species (S. townsendi) and especially strongly in the southern species (S. occidentalis). Both species showed positive climatic responses in the recent decade, when the recent breeding occupancy was greater than expected based on the historical contingency of occupancy-climate-coupling. This implies the potential climate adaptation or life history plasticity in the breeding warbler populations. However, the southern species (S. occidentalis) showed compromised climate response in 2000-10, when the predicted breeding occupancy was significantly lower than the expected contingency. I further evaluated the potential of breeding niche competition between the hybridizing warblers, reflected by their overlap of breeding occupancy. I found that the competition potential was the lowest in 2000-10 when both species were at the trough of breeding occupancy, which recovered in 2010-20. Future investigation of the physiological and behavioral mechanism underlying this climate change response could illuminate the effect of climate change on speciation and adaptation in the rainforest ecosystem.

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Trading places: opposite colonization and extinction responses of the hermit warbler and western bluebird to the 2021 Dixie Fire

Bielski,

Wood

2024

California Fish and Wildlife Journal

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Forty years of increasing fire size and severity in California’s Sierra Nevada were embodied by the 2021 Dixie Fire, which burned 389,837 ha between July and October, making it one of the largest, most destructive fires in California’s history. Historical fire regimes burned substantial areas annually, but primarily at low and moderate severities. Studies of the implications of fires like the Dixie Fire, which burn largely at higher severities, have focused on habitat change in the burned area; much less is known about potential edge effects. The hermit warbler (Setophaga occidentalis) and western bluebird (Sialia mexicana) have previously been characterized as species with dramatic, opposing post-wildfire responses: hermit warblers display a strongly negative response to fires while western bluebirds display a strong positive response. We conducted passive acoustic monitoring pre- and post-Dixie Fire inside and outside the burned area and analyzed the audio with the machine learning animal identification tool BirdNET. We then used a multi-season occupancy modeling framework to characterize both species’ site extinction and site colonization responses as a function of fire and habitat variables. We found no influence of edge effects, though this may have been a function of the low density of our recorders relative to the home range of these species. We did, however, observe contrasting relationships between the species. Hermit warbler site extinction was elevated in burned areas, particularly those burned at higher severities, while site colonization in unburned habitat was positively associated with canopy cover. Western bluebirds displayed the exact opposite pattern (elevated colonization in areas of high-severity fire, elevated extinction in unburned areas with high canopy cover). These results suggest contrasting trajectories for fire-influenced bird species under contemporary fire regimes and could guide hypothesis generation for broader studies of biodiversity responses to fire in this ecosystem.

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Can the Hermit Warbler ( Setophaga occidentalis ) serve as an old-forest indicator species in the Sierra Nevada?

Cited by 3 publications

References 39 publications

Assessing the potential of BirdNET to infer European bird communities from large-scale ecoacoustic data

Assessing the potential of BirdNET to infer European bird communities from large-scale ecoacoustic data

The dynamic climate adaptation of indicator warbler species complex in the Pacific Rainforest

Trading places: opposite colonization and extinction responses of the hermit warbler and western bluebird to the 2021 Dixie Fire

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