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 reproductive success of female waterfowl during egg laying and incubation (the nutrient-limitation hypothesis). We tested the nutrient-limitation hypothesis in Canvasbacks (Aythya valisineria) and Redheads (A, americana) by relating the body masses of incubating females with subsequent nest success, brood survival, and adult survival. Our analyses were based on 392 Canvasbacks and 76 Redheads captured and weighed during late incubation in southwestern Manitoba during 1983-1993. For Canvasbacks, 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 yearlings (P = 0.03). For Redheads, nest success was unrelated to body mass. For both species, brood survival and adult survival (i.e., return rates) were unrelated to female body mass. Thus, future reproductive success was correlated with body mass in only one out of seven test comparisons (i.e., nest success of yearling Canvasbacks). Although we had large sample sizes and used similar methods, our results were notably different from a previous study of prairie dabbling ducks (Anas spp.), where light-weight females were more likely to experience nest failure. For both studies, we believe that investigator-induced nest abandonment was an important cause of condition-dependent nest failure, We conclude that nutrient reserves were of minor importance in determining future reproductive success of adult Canvasbacks and Redheads, but may be important for yearlings.