Responses of birds to large-scale wildfires in southern California

Abstract

In 2002 and 2003, ~4000 km 2 of southern California burned in the region's largest fires in over a century. Within 1-2 years post-fire, we established 81 bird-survey routes (total-ing over 200 km) within the perimeters of the Pines, Cedar, and Coyote fires, and in nearby unburned habitat to serve as controls. We surveyed these routes repeatedly during both spring/ summer and winter for 5 years, with the objective of comparing species by pattern of response and identifying the species most strongly affected. Sampled habitat was primarily chaparral with isolated stands of oak woodland and coniferous forest. To quantify species' responses, we used data from the San Diego County Bird Atlas (1997-2002) as a pre-fire baseline, and used mixed-effects regression models to assess overall response to fire and post-fire trends. Responses and trends were diverse: in spring/summer, 24 species responded positively, 14 were neutral, and 43 responded negatively. In winter, 8 were positive, 18 neutral, and 34 negative. Some positive species (e.g., Lazuli Bunting, Passerina amoena) were strong "fire-followers," exploiting recently burned habitat, while others (e.g., Black-chinned Sparrow, Spizella atrogularis) increased mostly at higher elevations where forest was converted to chaparral. Neutral or "fire-resilient" species were either indifferent to fire (e.g., Ash-throated Flycatcher, Myiarchus cinerascens) or increased sharply after an initially negative response (e.g., Spotted Towhee, Pipilo maculatus). Among the negative or "fire-sensitive" species, recovery was often slow (e.g., California Thrasher, Toxostoma redivivum), and some continued to decline over time (e.g., Pygmy Nuthatch, Sitta pygmaea). By comparison with the pre-fire distribution as recorded in the atlas, the Rock Wren (Salpinctes obsoletus) was the strongest post-fire colonizer, while the Hutton's Vireo (Vireo huttoni) was the species most reduced. Small isolated breeding populations of the Red-breasted Sapsucker (Sphyrapicus ruber), Red-breasted Nuthatch (Sitta canadensis), Hermit Thrush (Catharus guttatus), Fox Sparrow (Passerella iliaca), and Golden-crowned Kinglet (Regulus satrapa) were eliminated from the Cuyamaca Mountains for at least the first 5 years after the fire. Annual rainfall during the study varied widely, slowing recovery in dry years. Variation in numbers of many species, especially granivorous winter visitors, paralleled variation in annual rainfall. If the area of southern California that burns annually increases as predicted, fire-followers should benefit, while species that are rare, patchily distributed, and dependent on later stages of succession will be most at risk. If the fires are a symptom of a shift toward a drier climate, they may cause a long-term or permanent reduction in numbers and ranges of fire-sensitive species.