DECISION RULES FOR SITE FIDELITY IN A MIGRATORY BIRD, THE PROTHONOTARY WARBLER

Abstract

I studied 787 female and 510 male Prothonotary Warblers (Protonotaria citrea) breeding in southern Illinois, USA, from 1994 to 2000 to test two competing hypotheses that may explain between-year breeding-site fidelity in migratory birds. I experimentally manipulated the nesting success of randomly chosen female (n = 187) and male (n = 139) warblers during 1997–2000 to test the “decision rules” hypothesis. The site fidelity of individuals increased significantly with an increase in the number of broods produced (zero, one, or two) and >80% of those that were double-brooded returned to sites the following year. Territory fidelity of individuals that returned to study sites also increased with increased reproductive success. The “renesting stress” hypothesis was not supported because site fidelity was unaffected by the number of nesting attempts made. Site fidelity did not differ between sexes, but territory fidelity was higher for males than for females. Mate fidelity, age, and brood parasitism by cowbirds had little effect on site and territory fidelity. Nesting success on Prothonotary Warbler territories was predictable between years, and individuals benefited by returning to territories where two broods were produced or by dispersing from territories where no broods were produced. These results support the decision rules hypothesis and demonstrate a causal relationship whereby individuals use their own reproductive experience at a site to assess the current and potential future quality of the location and then respond accordingly by returning or not returning. Decision rules may allow these birds to avoid sites with chronically high rates of nest predation and to concentrate in areas where nesting success is high. Corresponding Editor: R. Greenberg