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C <br />abundance in one or more habitat type or those with a wide distribution <br />(i.e., found in most habitat types sampled) . <br />Passerine Breeding Habitats <br />Juniper. More avian species were observed in the juniper vegetation type <br />than in any other type surveyed during the breeding passerine surveys <br />(12 species) . Accordingly, this type had the highest species diversity <br />index of any type surveyed in the study area (1.91) . The structural heter- <br />ogeneity of the juniper type with its tree stratum provide more opportun- <br />ities for nesting and feeding "niches" than other vegetation types in the <br />area; as a result, the type can support a greater variety of bird species <br />and a high population of. birds. This habitat supported the second highest <br />avian population (40.0 individeel s/km) . The most abundant species observed <br />in this habitat in decreasing order of relative abundance were; red-winged <br />blackbird, violet -green swallow, western meadowlark, and American robin. <br />Three passerine species that were encountered in the juniper vegetation. <br />type but not observed elsewhere during the June, 1979 census were ash - <br />throated flycatcher, blue eLosbeac and Cassin's finch. The western meadow- <br />lark and American robin exhibiteri an affinity for the juniper vegetation. <br />Alfalfa field. A total of'nine passerine species was encountered in the <br />alfalfa field. The most abundant species observed in decreasing order <br />of relative abundance were: red winged blackbird, violet -green swallow, <br />and cliff swallow. This habitat supported the highest total avian popu- <br />lation (45.3 individuals/km),and the third highest species diversity index <br />(1.25). The western flycatcher and black- billed magpie were observed <br />only in the alfalfa field during the breeding bird census. However, only <br />the violet green swallow exhibited a definite affinity for the alfalfa field. <br />Riparian. The riparian vegetation type supported a total of nine avian <br />species. The Shannon Weiner species diversity index in this habitat was <br />the second lowest of all types sampled (1.21) and the total avian popu- <br />lation was 36.0 individuals/km. The red - winged blackbird was the most. <br />a'bund nt species encountered along the riparian transect. Three passerine <br />specie:: observed in this vegetation type and not observed elsewhere <br />thr' June, 1679 census were long - billed marsh wren, orange-crowned wer'eler, <br />-32- <br />1UIi I 1 1483, <br />