and American robin. Most of the birds in the non- 

 willow habitat nested on the ground. The only ex- 

 ception was the red-winged blackbird, which we 

 found nesting in tall, thick sedge communities near 

 the stream. 



Of the 13 species breeding in the willow- 

 dominated beaver pond habitat, six (willow fly- 

 catcher, American robin, yellow warbler, song spar- 

 row, red-winged blackbird, and Brewer's blackbird) 

 nest in shrubs and feed on the ground, in bushes, or 

 in the air. Each of those species is oriented to de- 

 ciduous riparian plant communities for reproductive 

 and feeding activities (Thomas 1979). The killdeer, 

 spotted sandpiper, and common snipe nest on the 

 ground, usually but not necessarily near water 

 (Harrison 1979). At Summit Creek, we observed 

 them most often near the beaver pond in mesic her- 

 baceous communities dominated by grasses, sedges, 

 and rushes. Of the four species breeding in the 

 adjacent nonwillow habitat, three (vesper sparrow, 

 savannah sparrow, and western meadowlark) 

 nested and fed on the ground. Each is oriented 

 to dry meadow plant communities for reproduction 

 and feeding (Thomas 1979). In general, our obser- 

 vations of the habitats used by the birds breeding 

 on the Summit Creek site generally support those 

 reported by Douglas and Ratti (1984) for the 

 Centennial Mountains of eastern Idaho. 



Among the species found on the two study plots, 

 only the American robin and Brewer's blackbird 

 were assigned medium or high versatility ratings 

 with respect to the number of plant communities 

 used for reproductive or feeding activities; all others 

 were g^ven low versatility ratings by Thomas (1979). 

 Five of the species found in the beaver pond complex 

 at Summit Creek — the common snipe, willow fly- 

 catcher, yellow warbler, common yellowthroat, and 

 song sparrow — appear ecologically dependent upon 

 riparian vegetation for breeding habitat (Knopf and 

 Samson 1988). 



CONCLUSIONS 



We found sharply defined structural (physiog- 

 nomic) differences in vegetation between a willow- 

 dominated beaver pond complex and an adjacent 

 nonwillow riparian habitat. Differences were most 

 pronounced in the overstory layer where average 

 values of shrub biomass, shrub height, and shrub 

 canopy cover were significantly higher on the beaver 

 pond site. Those differences, plus the availability of 

 impounded water, were reflected in the composition 

 and density of associated breeding bird populations. 

 Our estimates of total breeding bird density, bird 

 species richness and diversity, and total breeding 

 bird biomass were markedly higher in the beaver 

 pond habitat. Further, more foraging and nesting 



guilds were represented in the beaver pond complex 

 than in the adjacent riparian habitat. Our findings 

 suggest that beaver pond ecosystems can provide 

 important habitats for nongame breeding birds in 

 the Western United States. 



ACKNOWLEDGMENTS 



We gratefully acknowledge the field and office 

 assistance of John W. Kinney, Sherri A. Brown, 

 Justine L. Wirch, Kevin Tom, and Patrick V. 

 Turner. Lyle A. Lewis, Caryl Elzinga, Loren D. 

 Anderson, and Gloria Romero provided unpublished 

 information about the study area and grazing 

 history. 



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American Ornithologists' Union. 1983. Check -list 

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Anderson, Loren D. 1989. [Personal communica- 

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Brown, James K 1976. Estimating shrub biomass 

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Daubenmire, R. 1959. A canopy-coverage method 

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DeGraaf, Richard M.; Tilghman, Nancy G.; 

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Douglas, David C; Ratti, John T. 1984. Avian habi- 

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Dunning, John B., Jr. 1984. Body weights of 686 

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 38 p. 



Harrison, Hal H. 1979. A field guide to western 

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Hill, Edward P. 1982. Beaver. In: Chapman, 

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Hill, M. 0. 1973. Diversity and evenness: a unifying 

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Hitchcock, C. Leo; Cronquist, Arthur. 1973. Flora 

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