THE EFFECTS OF LATE-INCUBATION BODY-MASS ON REPRODUCTIVE SUCCESS AND SURVIVAL OF CANVASBACKS AND REDHEADS

Intraspecific variation in nutrient reserves is believed to affect rep roductive success of female waterfowl during egg laying and incubation (the nutrient-limitation hypothesis). We tested the nutrient-limitati on hypothesis in Canvasbacks (Aythya valisineria) and Redheads (A, ame ricana) by relating the body masses of incubating females with subsequ ent nest success, brood survival, and adult survival. Our analyses wer e based on 392 Canvasbacks and 76 Redheads captured and weighed during late incubation in southwestern Manitoba during 1983-1993. For Canvas backs, there was a significant interaction between body mass and age; failed adults (ASY) weighed 3 g more than successful adults (P = 0.65) , but failed yearlings (SY) weighed 37 g less than successful yearling s (P = 0.03). For Redheads, nest success was unrelated to body mass. F or both species, brood survival and adult survival (i.e., return rates ) were unrelated to female body mass. Thus, future reproductive succes s was correlated with body mass in only one out of seven test comparis ons (i.e., nest success of yearling Canvasbacks). Although we had larg e sample sizes and used similar methods, our results were notably diff erent from a previous study of prairie dabbling ducks (Anas spp.), whe re light-weight females were more likely to experience nest failure. F or both studies, we believe that investigator-induced nest abandonment was an important cause of condition-dependent nest failure, We conclu de that nutrient reserves were of minor importance in determining futu re reproductive success of adult Canvasbacks and Redheads, but may be important for yearlings.