Avian Community Structure Along a Mountain Big Sagebrush Successional Gradient

Abstract

We compared vegetative structure and bird communities among 4 successional states in central Oregon representing a continuum from 1) postburn grassland, 2) mountain big sagebrush—Idaho fescue (Artemisia tridentatA—Festuca idahoensis) shrub—steppe, 3) sagebrush—steppe—juniper (Juniperus occidentalis), to 4) old‐growth western juniper. Species richness, evenness, and diversity of bird communities were highest in old‐growth and mid‐successional juniper (22.9 species/transect and 23.6 species/transect, respectively) but lowest in the grasslands (17.6 species/transect). Bird species diversity was positively correlated with physiognomic cover diversity (r = 0.74, P = 0.001). Density of breeding birds was greatest in old‐growth juniper (6.6 birds/ha) and lowest in postburn grasslands (3.6 birds/ha) but similar in shrub—steppe and sagebrush—steppe—juniper (6.0 birds/ha and 5.5 birds/ha, respectively). Old‐growth juniper had the highest total densities of both tree and cavity nesters. Mountain chickadees (Parus gambeli), Cassin's finches (Carpodacus cassinii), chipping sparrows (Spizella passerina), brown‐headed cowbirds (Molothrus ater), mountain bluebirds (Sialia currucoides), dark‐eyed juncos (Junco hyemalis), Empidonax flycatchers, ash‐throated flycatchers (Myiarchus cinerascens), and northern flickers (Colaptes auratus) were more abundant in cover types dominated by junipers. Vesper sparrows (Pooecetes gramineus), western meadowlarks (Sturnella neglecta), green‐tailed towhees (Pipilo chlorurus), and horned larks (Eremophila alpestris) were associated with grassland communities. Brewer's sparrows (Spizella breweri), sage sparrows (Amphispiza belli), sage thrashers (Oreoscoptes montanus), and horned larks (Eremophila alpestris) were most abundant in sagebrush cover types. Management strategies should restore or maintain the desired proportions of the different successional states to maintain populations of grassland and sagebrush birds while providing habitat for tree and cavity nesting species.

Structural heterogeneity increases diversity of non‐breeding grassland birds

“…Our findings concur with breeding bird research from other rangeland systems that indicated bird community composition is dependent on variable patterns of fire and grazing (Knopf 1994, Skowno and Bond 2003, Krook et al 2007, Reinkensmeyer et al 2007, Gregory et al 2010). This makes intuitive sense when you consider the historical disturbance regime of grasslands and the affinity of grassland breeding birds to select areas with specific, varying levels of biomass (Knopf 1994).…”

Persistence of Western Juniper (Juniperus occidentalis) Resource Islands Following Canopy Removal

“…Greater distances represented bird assemblages that were increasingly dissimilar to sagebrush bird communities and more representative of juniper woodlands (Balda and Masters 1980;Sedgwick 1987;Rosenstock and van Riper 2001;Reinkensmeyer et al 2007). The underlying gradient separating treatment points from the sagebrush bird community was a function primarily of competing sagebrush and piñon-juniper cover; decreased sagebrush and increased piñon-juniper cover resulted in greater ecological distances to the sagebrush bird community.…”

Remote sensing of vegetation 3‐D structure for biodiversity and habitat: Review and implications for lidar and radar spaceborne missions

“…Biomass is one of the indirect indicators of age, density, successional stage, and productivity – important factors known to influence habitat selection and biodiversity [ Petranka et al , 1994; Sorensen and Fedigan , 2000; Reinkensmeyer et al , 2007; Martinuzzi et al , 2009b]. Recently, radar‐derived biomass has been used to improve species habitat models [ Bergen et al , 2007].…”