Ghosts of habitats past: Contribution of landscape change to current habitats used by shrubland birds

Models of habitat associations for species often are developed with an impl icit assumption that habitats are static, even though recent disturbance ma y have altered the landscape. We tested our hypothesis that trajectory and magnitude of habitat change influenced observed distribution and abundance of passerine birds breeding in shrubsteppe habitats of southwestern Idaho. Birds in this region live in dynamic landscapes undergoing predominantly la rge-scale, radical, and unidirectional habitat change because wildfires are converting shrublands into expanses of exotic annual grasslands. We used d ata from field surveys and satellite image analyses in a series of redundan cy analyses to partition variances and to determine the relative contributi on of habitat change and current landscapes. Although current habitats expl ained a greater proportion of total variation, changes in habitat and measu res of habitat richness and texture also contributed to variation in abunda nce of Horned Larks (Eremophila alpestris), Brewer's Sparrows (Spizella bre weri), and Sage Sparrows (Amphispiza belli). Abundance of birds was insensi tive to scale for nonspatial habitat variables. In contrast, spatial measur es of habitat richness and texture in the landscape were significant only a t large spatial scales. Abundance of Horned Larks, Western Meadowlarks (Stu rnella neglecta), and Brewer's Sparrows, but not Sage Thrashers (Oreoscopte s montanus) or Sage Sparrows, was positively correlated with changes toward stable habitats. Because dominant habitat changes were toward less stable conditions, regional declines of those birds in shrubsteppe habitats reflec t current landscapes as well as the history, magnitude, and trajectory of h abitat change.