Foraging Patch Selection by Shrubsteppe Sparrows

We used bird-centered vegetation measurements to assess selection of shrub-defined patches by foraging Sage Sparrows (Amphispiza belli) and Brewer’s Sparrows (Spizella breweri) over a period of 3 yr. Principal components of habitat variation based on a random sample of 900 patches were patch size, species composition (big sagebrush [Artemisia tridentata] vs. green rabbitbrush [Chrysothamnus viscidiflora] vs. gray rabbitbrush [C. nauseosus]), and plant vigor. Both bird species differed from random (P < 0.001) in their selection of patches in each year, but did not differ from each other. Patch structure varied significantly among years (P < 0.001), as did each species’ use of patches. Between-year changes in the two bird species’ selection patterns were highly correlated with changes in the habitat, and with each other. These correlations suggest that shrubsteppe sparrows “track” interannual variation in patch composition and structure (which is presumably induced by precipitation variation) but maintain nonrandom use patterns within years.