TERRITORY-SIZE REGULATION IN BLACK-SHOULDERED KITES

We studied the relationship of Black-shouldered Kite (Elanus caeruleus ) territory size to prey abundance and competitor abundance in northwe stern California. Kite territory size ranged from 1.6 to 21.5 ha (n = 26). The estimated mean number of California voles (Microtus californi cus) per territory was 1,483 +/- SE of 163 (n = 25). Competitor abunda nce (i.e. total raptor abundance) ranged from 4.8 to 31.0 individuals/ km2 and was strongly correlated with abundance of M. californicus. Bot h estimated prey abundance and competitor abundance were inversely cor related with kite territory size. After developing multiple-regression models using both variables, partial-correlation analysis revealed th at once the effects of prey abundance were statistically controlled, c ompetitor abundance continued to be significantly correlated with kite territory size. When the effects of competitor abundance were statist ically controlled, prey abundance was no longer significantly correlat ed with kite territory size. In that it appears that the number of com petitors was a function of number of prey, we conclude that kite terri tory size is proximately regulated by competitor abundance and ultimat ely regulated by prey abundance.