Riparian zones provide habitat for breeding birds in the semiarid western United
States; however, there are few data available that address the effects of livestock grazing
strategies on riparian habitats and avian communities. Documenting avian community
composition in different riparian vegetation communities and relating vegetation
communities to livestock grazing strategies may identify management alternatives that
are sustainable from a wildlife habitat perspective, and may permit constructive coalitions
between agricultural industry and environmental groups. I compared diurnal breeding
bird abundance, individual species abundance, and species richness, and vegetation
composition and structure among 12 streamside riparian areas of Bear and Silvies valleys
in eastern Oregon during 1993 and 1994. Bird and vegetation data were collected along
four replicate transects within each of three riparian vegetation communities
characterized by vegetation structure: herbaceous, discontinuous willow (Salix spp.), and
continuous willow. These riparian vegetation communities were grazed under summer
season-long, summer short-duration, and fall short-duration livestock grazing strategies,
respectively, >5 years before the study.
Differences in riparian vegetation among communities were primarily related to
shrub structure by experimental design. The continuous willow community had more
shrub cover overall (P<0.001) and within each 1-m height interval from 0-4 m
(P<0.013) than the herbaceous and discontinuous willow communities. The herbaceous
community had no shrub cover >1 m in height. Willows extended farther (P=0.031)
from the steam edge in the continuous willow community than in the discontinuous
willow community. No willows were detected in the herbaceous community.
I detected 4,016 birds representing 56 species along the transects. Total bird
abundance was greater (P<0.001) in the continuous willow community than in the
herbaceous and discontinuous willow communities. Species richness was inconsistent
(P=0.034) between years within communities; it was greatest (P<0.037) in the
continuous and discontinuous willow communities in 1993, and greatest (P<0.003) in
the continuous willow community in 1994. Total bird abundance and species richness in
1994 increased with willow volume (r��>0.707, P<0.001). Of 23 bird species with >20
individual detections over both years, 13 species were most abundant in one or two
vegetation communities (P<0.088). Seven species (yellow warbler [Dendroica
petechia], song sparrow [Melospiza melodia], willow flycatcher [Empidonax traillii],
American robin [Turdus migratorius], common snipe [Gallinago gallinago], bobolink
[Dolichonyx oryzivorus], and Vaux's swift [Chaetura vauxi]) were most abundant in the
continuous willow community. Three species (savannah sparrow [Passerculus
sandwichensis], black tern [Chlidonias niger], and American wigeon [Anas americana])
were most abundant in the herbaceous community. Willets (Catoptrophorus
semipalmatus) were most abundant in the herbaceous and discontinuous willow
communities whereas cinnamon teal (A. cyanoptera) were most abundant in the
herbaceous and continuous willow communities. Red-winged blackbirds (Ageliaus
phoeniceus) were inconsistent (P=0.032) between years within communities: they were
most abundant in the continuous willow community in 1993, and most abundant in the
continuous willow and herbaceous communities in 1994.
Hydrophytic woody vegetation within semiarid rangeland environments increases
structural complexity and is associated with avian abundance and diversity. Yellow
warblers, willow flycatchers, and song sparrows, which depend on hydrophytic shrubs for
nesting almost exclusively in the semiarid West, are especially threatened by the
elimination or simplification of woody riparian vegetation. I suggest that riparian
vegetation structure and composition, which is associated with avian abundance, species
richness, riparian associate bird species, and landscape-level biological diversity, be
maintained where possible. Seasonal light (<30% use) fall short-duration grazing seemed
to be compatible with the maintenance of woody riparian vegetation whereas summer
season-long and summer short-duration grazing is likely incompatible. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35190 |
| Date | 12 May 1995 |
| Creators | Sanders, Todd Alan |
| Contributors | Edge, W. Daniel |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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