Breeding biology, extra-pair birds, productivity, siblicide and conservation of the Madagascar Fish Eagle

Madagascar Fish Eagles Haliaeetus vociferoides laid eggs over a 53-day period from the end of May to mid-July. The incubation period ranged from 37 to 43 days with a mean of 39.7 days and 95% confidence interval of +/- 2.3 days. Eggs hatched over a 46-day period from 5 July to 20 August with a mean hatch date of 23 July, and a 95% confidence interval of 18 to 28 July. Nestling periods ranged from 78 to 89 days and averaged 82 days. Mean fledging date was calculated from mean hatching date as 9 to 20 September, with a 95% confidence interval from 31 August to 29 September. Clutch size was determined in 35 cases, of which seven (20%) were single-egg and 28 were two-egg clutches. Productivity from occupied territories was 0.15 fledged young/territory in 65 pair-years. Sibling rescue in three years increased productivity to 0.28 young/territory. Apart from failure to lay eggs, which accounted for 21 of the 55 instances, siblicide accounted for most of the reduced productivity. Human removal of nestlings for food and to keep in captivity accounted for a large proportion of the total breeding failures. The most unusual behaviour observed was the presence of an extra-pair bird in the immediate proximity of a breeding pair in 40 (42%) of 95 pair-years, at 41 nest sites (the status of every pair was not determined every year). Extra-pair birds participated briefly in incubation and nestling-period activities in each of two observed nests. Banding evidence suggests that extra-pair birds are progeny from previous years that have delayed dispersal, but sample size is too small to be conclusive.