ASSOCIATION OF WITHIN-TERRITORY VEGETATION CHARACTERISTICS AND FITNESS COMPONENTS OF CALIFORNIA GNATCATCHERS

Correlations among habitat characteristics and fitness components of C alifornia Gnatcatchers (Polioptila californica californica) were exami ned using within-territory vegetation and life-history data for 41 pai rs of gnatcatchers at four sites from 1993 through 1995. Gnatcatchers nested earlier, had more successful nests, produced more fledglings, h ad a longer nesting period, and had lower fledgling costs when their t erritories were associated with increased grass and forb cover, increa sed perennial structure, increased horizontal perennial homogeneity, d ecreased vertical perennial homogeneity, and decreased perennial diver sity. Within-territory Vegetation variables, derived from the correlat ion of vegetation and life-history variables, were able to discriminat e among gnatcatcher pairs grouped by site. Survival of adult gnatcatch ers was significantly higher in the gnatcatcher group that had average within-territory vegetation characteristics associated with maximizat ion of other life-history variables and was significantly lower in the gnatcatcher group that had average within-territory vegetation charac teristics associated with minimization of other life-history variables . Survival of juveniles was not associated with within-territory veget ation. The finite rate of population increase (lambda) was >1 for the gnatcatcher group where within-territory vegetation and life-history v ariables were maximized, approximately equal to 1 for gnatcatcher grou ps where within-territory vegetation and life-history variables were m oderate, and <1 for the gnatcatcher group where within-territory veget ation and life-history variables were minimal. Our study suggests that within-territory vegetation characteristics are associated with adult survival and lambda, but site characteristics independent of vegetati on also could have contributed to such an association.