HABITAT ASSOCIATIONS, RELATIVE ABUNDANCE, AND SPECIES RICHNESS OF AUTUMN LANDBIRD MIGRANTS IN SOUTHWESTERN IDAHO

We used count surveys and mist-net captures to compare habitat associations, relative abundance, species richness, and community similarity of migrant landbirds among four major habitats in the Boise Foothills of southwestern Idaho. Count surveys were con- ducted from August through October 1997-2000 in conifer forest, mountain shrubland, shrubsteppe, and riparian shrubland. We compared bird detections among habitats for all birds pooled, individual species, and three migration strategies: Neotropical, temperate, and resident (including irruptive migrants). Mountain shrubland supported the highest numbers of temperate migrants; both mountain shrubland and riparian shrubland had the highest numbers of Neotropical migrants; and conifer forest had the highest numbers of residents. Species richness was highest in riparian shrubland and lowest in shrubsteppe, whereas di- versity and evenness were highest in conifer forest and mountain shrubland. Mist netting was conducted from mid-July to mid-October in two habitats: mountain shrubland (1997- 2002) and riparian shrubland (1998-1999). Captures (adjusted for effort) were compared among habitats in 1998-1999 and were similar for temperate migrants, whereas mountain shrubland had higher abundance of Neotropical migrants and riparian shrubland had higher abundance of irruptive migrants. Richness, diversity, and evenness were similar and there was high community similarity between mountain shrub and riparian shrubland habitats. These results emphasize the importance of montane habitats, especially deciduous shrub communities, to migrants in the Intermountain West.