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abundance in one or mre habitat type or t7ose witr, a wide distribution. <br /> (i.e. , found in Trost 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) . he structural heter- <br /> ogeneity of the juniper type with its tree stratu--n provide more opportun- <br /> ities for nesting and feeding "niches" t;•i,n 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 hig:.est <br /> avian population (40.0 individuals/}an) . The Est abundant species observed <br /> in this habitat in decreasing order of relative abundance were: red-winged <br /> blackbird, violet-green swallow, western meadowlark, and A-nerican 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 grosbeak and Cassia's finch. The western meadow- <br /> lark and American robin exhibited an affinity for the juniper vegetation. <br /> Alfalfa field. A total of nine passerine species was encountered in t.e <br /> alfalfa field. The Trost 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) ,anal the third highest species diversity i:.dex <br /> (1.25) . Try western flycatcher and 'black-billed magpie were observed <br /> only in the alfalfa field during the breeding bird census. However, o:.ly <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/}cn. The red-winged blackbird was the m.st <br /> aburl,int species encountered along the riparian. transect. ':nree passerine <br /> species observed in this vegetation type and not observed else�Kt re curijig <br /> th.- June, ]979 census were :onc-bi.lI EYi marsh wren, orange-c:r,.'•e <br /> -32- <br /> JUMii1�80 <br />