Breeding ecology and nestling growth of the Madagascar Pond Heron Ardeola idae in a monospecific colony at Sofia Lake, northern Madagascar

Abstract

The breeding ecology of the endangered Madagascar Pond Heron Ardeola idae was studied at Sofia Lake, northern Madagascar, during two consecutive breeding seasons (October 2017–April 2018 and October 2018– April 2019). Altogether 158 nests were documented at a monospecific breeding colony for both seasons combined. The breeding season occurred between November and April. Nest construction started from the middle of November and it took 8.2 ± 2.5 d on average to complete a nest (n = 158 nests, range = 5–13 d). All the nests were build inside clusters of Papyrus Cyperus madagascariensis. The nest density was 0.31 nests m−2 and 0.20 nests m−2 for Season 1 and Season 2, respectively. Egg laying took place between November and January, but it continued throughout February for renesting attempts (second clutches laid). Mean clutch size was 2.9 ± 0.68 eggs (n = 158, range = 2–4). Incubation started with the laying of the first egg, producing an asynchronous hatching. The incubation period averaged 20.6 ± 0.9 d (n = 158, range = 20–22 d). Of the 461 eggs laid in 158 nests, 399 (86.6%) hatched, and 326 (70.7%) of those hatchlings fledged, a reproductive success of 2.06 fledglings per nesting attempt. Data obtained from 34 measured nestlings showed a rapid growth of all measured biometric parameters, except for tarsus length. The mean daily growth rate was 9.02 g for body mass, 9.64 mm for body size length, 10.66 mm for wing length and 2.35 mm for tarsus length. Significant differences were recorded in growth rates between nestlings in the same brood in relation to their hatching sequence. The last nestlings to hatch had lower growth rates for all measured parameters than their older siblings.