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 peri od 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 da ys. 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. Nest ling 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 deter mined 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/te rritory in 65 pair-years. Sibling rescue in three years increased productiv ity to 0.28 young/territory. Apart from failure to lay eggs, which accounte d for 21 of the 55 instances, siblicide accounted for most of the reduced p roductivity. Human removal of nestlings for food and to keep in captivity a ccounted 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 ac tivities in each of two observed nests. Banding evidence suggests that extr a-pair birds are progeny from previous years that have delayed dispersal, b ut sample size is too small to be conclusive.