New insights on the breeding biology of the Crow Honeyeater Gymnomyza aubryana suggest convergence with the Mao G. samoensis

Abstract

Phylogenetic study of the honeyeater family shows that the four insular species of the genus Gymnomyza are polyphyletic, with the largest, the Crow Honeyeater G. aubryana, being a distinct and ancient lineage. The Critically Endangered Crow Honeyeater is a secretive species that lives in the rainforest of New Caledonia. For two breeding seasons (S1 in 2019 and S2 in 2020) we studied its breeding biology in the Parc Provincial de la Rivière Bleue. In S1, three nests (N1, N2, N3) were found and one nest (N4) in S2. Three dismantled nests (N1, N2 and N4) revealed four distinct layers; detailed measurements showed that Nest N2 consisted of 507 pieces of nest material and weighed 103 g. The female built the nest and incubated the one-egg clutch for 75% of time over a 24-hour period. The female rolled the egg each 33 minutes (n = 50) during the day and 118 minutes (n = 23) at night. The nest was 9.5 m above ground in a small tree (trunk 12 cm in diameter) and the trees and shrubs within 10 m mainly had trunks ⩽10 cm in diameter (n = 4). Laying occurred during the dry season (August–October). The feeding rate of the nestling was 2.6 times/h. Animal prey items accounted for 74.7% by number, of which 66.5% were orthopterans; indeterminate 9.7%, fruit 12.4% and only 3.2% was nectar (n = 1788). Prey items in the size range 21–40 mm in length constituted 59% of the nestlings’ food by number. The number of faecal sacs produced per nestling averaged 1.7/h (n = 956). The young fledged at 25.5 days (mean for two nests) and did not return to the nest, but was fed for another 2.6 months. One juvenile, from an unknown nest, remained at least 16.5 months in the adults’ territory. The home range of a male during 2.6 months (September to early December) was 24 ha. The Crow Honeyeater has a slow life history for breeding biology, as found also for the Mao G. samoensis. Both species evolved on tropical islands and show a convergent adaptation.