Importance of Montane Riparian Forest and Influence of Wildfire on Nest‐Site Selection of Ground‐Nesting Birds

Abstract

Abstract: We studied breeding populations of 2 coexisting ground‐nesting birds, the red‐faced warbler (Cardellina rubrifrons) and yellow‐eyed junco (Junco phaeonotus), in high‐elevation (>2,000 m) forested drainages of the Santa Catalina Mountains, Arizona, USA. From 2004 to 2005, we 1) estimated density and nesting success of breeding populations of red‐faced warblers and yellow‐eyed juncos, 2) identified nest‐site characteristics for each species (i.e., used sites vs. random plots), 3) compared nest‐site characteristics between the 2 species, and 4) examined effects of a recent (2003) wildfire on distribution of nests of both species. In addition, we estimated the areal extent of montane riparian forest (the preferred breeding habitat of both species) within high‐elevation forests of the Santa Catalina Mountains. We found that red‐faced warblers and yellow‐eyed juncos were the 2 most common ground‐nesting birds within our study area with an average density of 2.4 and 1.4 singing males/ha, respectively, along drainage bottoms. Compared to random plots, most red‐faced warbler and yellow‐eyed junco nests were located close (≤30 m) to drainage bottoms within a strip of montane riparian forest characterized by abundant brush, small woody debris, ferns, and forbs (both species), high number and diversity of saplings and small trees (red‐faced warblers), and abundant shrubs and downed logs and less canopy cover (yellow‐eyed juncos). Although both species nested in close proximity within montane riparian forest, nest‐site characteristics differed between the 2 species, especially at finer spatial scales. For example, most yellow‐eyed juncos nested adjacent to grass (principally Muhlenbergia spp.), whereas red‐faced warblers nested adjacent to a variety of plant species, including grass, bigtooth maple (Acer grandidentatum), white fir (Abies concolor), and Douglas‐fir (Pseudotsuga menziesii). Both red‐faced warblers and yellow‐eyed juncos avoided nesting in areas burned during a recent wildfire. In addition, nesting success was low for red‐faced warblers (13%) and yellow‐eyed juncos (19%) following the wildfire, suggesting an indirect negative effect of fire on breeding populations in the short‐term. Montane riparian forest appears to provide important breeding habitat for red‐faced warblers and yellow‐eyed juncos. However, little research or conservation planning has been directed toward montane riparian forest in the region, even though this forest type is limited in its areal extent (<11% of high‐elevation forest in the Santa Catalina Mountains) and increasingly threatened by disturbance. Results from our study can be used to facilitate the management and conservation of breeding populations of red‐faced warblers and yellow‐eyed juncos in high‐elevation forests of the southwestern United States.