White-bellied Sea Eagle - Taxonomy

Taxonomy

The White-bellied Sea Eagle was first described by the German naturalist Johann Friedrich Gmelin in 1788, although John Latham had made notes on the species in 1781, from a specimen obtained in February 1780 at Princes Island off the westernmost cape of Java during Captain Cook's last voyage. Its specific name is derived from the Ancient Greek leuko- 'white', and gaster 'belly'. Its closest relative is the little-known Sanford's Sea Eagle of the Solomon Islands. These form a superspecies, and as is usual in other sea eagle superspecies, one (the White-bellied Sea Eagle) has a white head, as opposed to the other species' dark head. The bill and eyes are dark, and the talons are dark yellow as in all Southern Hemisphere sea eagles. Both these species have at least some dark colouration in their tails, though this may not always be clearly visible in the White-bellied Sea Eagle. The nucleotide sequences of the cytochrome b gene of the two sea eagles were among those analysed in a 1996 study. Although they differ greatly in appearance and ecology, their genetic divergence of 0.3% indicates that the ancestors of the two forms might have diverged as recently as 150,000 years ago. The study authors conclude that although the genetic divergence is more consistent with subspecies, the distinctness in appearance and behaviour warrants the two being retained as separate species. Mitochondrial sequence of the cytochrome b locus differs very slightly from that of Sanford's Sea Eagle suggesting a relatively recent divergence after New Guinea-based White-bellied Sea Eagles colonised the Solomon Islands.

The White-bellied Sea Eagle's affinities beyond the Sanford's Sea Eagle are a little less clear; molecular data indicate that it is one of four species of tropical sea eagle (along with the African Fish Eagle and the Madagascar Fish Eagle), while allozyme data indicate it might have a closer relationship with the sea eagles of the northern hemisphere. A further molecular study published in 2005 showed the White-bellied and Sanford's Sea Eagles to be basal to the four fish eagles (the two mentioned above plus the two hitherto untested species of the genus Ichthyophaga).

As well as White-bellied Sea Eagle and White-breasted Sea Eagle, other recorded names include White-bellied Fish-hawk, White-eagle, and Grey-backed Sea Eagle.