Brood Size in Canada Geese: A Manipulation Experiment

Abstract

SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size. SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size. SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size. SUMMARY (1) A brood size manipulation experiment was carried out on Canada geese Branta canadensis to examine the effects of brood size on both goslings and adults. Because brood size was manipulated, it could be interpreted unequivocally as the cause of any observed relationship, while the results could still be examined for a relationship between parental ability and clutch size. (2) Brood size (within the normal range) had no effect on the survival or weight of the goslings to fledging, or on their subsequent survival, growth or reproduction. Gosling survival was correlated with other factors including weather and male size. (3) There was no evidence for a correlation between clutch size and parental ability. (4) Brood size had deleterious effects on the condition (weight and timing of moult) of the female. These effects were not reflected in overwinter survival, but pairs with larger broods bred later the following year. Clutch size in the following year, and the condition of the male at the end of the breeding season were unaffected by brood size.