PARENT SESSION
Oral Session #23: Animal Ecology: Behavior and Sociobiology. Presiding: P. Brunkow.
Tuesday, August 7, 2001. 8:00 AM to 11:45 AM. Hall of Ideas E.

Decision rules for Prothonotary Warblers: the influence of nesting success on site fidelity.

Hoover, Jeffrey¹, ¹

ABSTRACT- Several hypotheses have been proposed to explain patterns of avian site fidelity but there is little consensus concerning the ultimate causes. I studied populations of Prothonotary Warblers (Protonotaria citrea) breeding in bottomland and swamp forests in southern Illinois, USA from 1994-2000 and experimentally manipulated the nesting success of randomly chosen pairs of warblers (1997-1999) to test two hypotheses that may explain patterns of between-year breeding-site fidelity in migratory songbirds. The two hypotheses that I considered were: (1) the Decision Rules Hypothesis, which states that patterns of between-year site fidelity are a result of experience-based choices (decision rules) by individuals and not simply a result of differential mortality; and (2) the Renesting Stress Hypothesis, which states that individuals experiencing high rates of nest predation also experience an increase in stress associated with renesting resulting in higher between-year mortality and lower rates of return. Females returned at rates of 19, 53, and 81%, and males at rates of 42, 58, and 83% for individuals producing 0, 1, or 2 broods, respectively. The territory fidelity of those individuals that returned also increased with increased reproductive success. Other factors such as mate fidelity, age, sex, and brood parasitism by cowbirds had relatively little influence on between-year returns and territory fidelity. 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 respond accordingly by returning or not returning to sites and territories. The renesting stress hypothesis was not supported. Decision rules may allow these birds to avoid chronically high rates of nest predation by not returning to areas where nest predation prevents nesting success.

KEY WORDS: site fidelity, decision rules, prothonotary warbler, nest predation