common species were the savannah sparrow (Pas- 

 serculus sandwichensis). Brewer's blackbird {Eu- 

 phagus cyanocephalus), yellow warbler (Dendroica 

 petechia), willow flycatcher {Empidonax traillii), 

 and red-winged blackbird (Agelaius phoeniceus). 

 Collectively, those five species accounted for over 

 80 percent of the breeding bird community. Other 

 common species included the western meadowlark 

 {Sturnella neglecta), vesper sparrow (Pooecetes 

 gramineus), and song sparrow {Melospiza melodia). 

 Wide-ranging raptorial birds, although commonly 

 seen, were not included in our analysis. Transient 

 species were also excluded. 



Breeding bird densities were markedly different 

 on the two study plots (table 2). Total bird density 

 in the beaver pond habitat (10.11 birds/ha) was 

 three times that of the adjacent riparian habitat 

 (3.38 birds/ha). Similarly, our estimate of total 

 breeding bird biomass was appreciably higher 

 (422 g/ha versus 121 g/ha) in the willow-dominated 

 beaver pond complex. Further, bird species rich- 

 ness and bird species diversity values were 3.25 and 

 1.67 times higher, respectively, in the beaver pond 

 habitat. 



Total breeding bird density recorded in the beaver 

 pond habitat at Summit Creek exceeds densities 

 found in most North American rangeland habitats 

 (Wiens and Dyer 1975) and compares favorably with 

 those of coniferous forests throughout North Amer- 

 ica (Wiens 1978). But Johnson and others (1980) 

 list breeding bird densities in riparian wetlands, 

 especially cottonwood-willow habitats in the south- 

 western United States, that are substantially higher 

 than those we found at Summit Creek. 



There were important organizational differences 

 between the two breeding bird communities of the 

 beaver pond complex and the adjacent riparian 

 habitat. Numerically, the dominant species on 

 the beaver pond area were Brewer's blackbirds. 



savannah sparrows, yellow warblers, and willow 

 flycatchers (table 2). Those four species made up 

 84 percent of the breeding bird community in the 

 beaver pond habitat. Shorebirds — killdeer {Charad- 

 rius vociferus), spotted sandpiper {Actitis macu- 

 laria), and common snipe {Gallinago galUnago) — 

 were present in low densities. They were found as 

 breeding birds only near the beaver pond; none bred 

 in the nonponded riparian habitat. The American 

 robin (Tardus migratorius) and common yellow- 

 throat (Geothlypis trichas) also bred only in the 

 beaver pond habitat. Of the four species breeding 

 in the nonwillow riparian habitat, all were included 

 among the much larger number of species that bred 

 in the beaver pond habitat. Only the savannah 

 sparrow showed a clear pattern of numerical domi- 

 nance within the nonwillow habitat. 



Birds may be placed in categories, or guilds, 

 based on similarities in their use of environmental 

 resources (Root 1967). The breeding bird species 

 listed in table 2 were organized into feeding and 

 nesting guilds based on their foraging behavior and 

 the substrates used for nesting (table 3). Birds that 

 forage or probe for food on the ground formed the 

 largest single category. That guild accounted for 

 66 percent of the breeding bird population in the 

 beaver pond habitat and 88 percent in the non- 

 willow riparian habitat. These, along with the 

 lower-canopy feeders, made up the largest fraction 

 of all feeding guilds in the beaver pond habitat. 

 Aerial-sally feeders were represented by a single 

 species — the willow flycatcher. Only ground feeders 

 were found in the nonwillow habitat. 



Ground and ground-bush nesters occurred in simi- 

 lar densities in the beaver pond habitat (table 3). 

 Numerically, those species accounted for 75 percent 

 of the breeding bird population in the beaver pond 

 habitat. Bush or small tree nesters were repre- 

 sented by the willow flycatcher, yellow warbler. 



Table 3 — Guild structure of breeding birds in a beaver pond complex (willow) and adjacent 

 (nonwillow) riparian habitat, Summit Creek, ID, 1989 



Beaver pond Adjacent 

 Guild (willow) (nonwillow) 





Number/ha 



Percent 



Number/ha 



Percent 



Foraging 











Ground-shoreline gleaning 



0.78 



8 



0.40 



12 



Ground foraging-probing 



6.65 



66 



2.98 



88 



Aerial-sally feeding 



1.04 



10 











Lower canopy gleaning-foraging 



1.64 



16 











Nesting 











Ground nesting 



3.07 



30 



2.78 



82 



Ground-bush nesting 



4.51 



45 











Bush-small tree nesting 



2.33 



23 











Cattail, rush, sedge nesting 



.20 



2 



.60 



18 



4 



