An uncommon resident of local forests and threatened sanctuaries, the little spiderhunter is a drab cousin of sunbirds with a bill that gives it the reach to probe the deep nectaries of zingiberaceous plants and pluck arachnids from three-dimensional webs. Seldom still for more than a second, it was sheer luck than uncultivated skill that offered a glimpse of this individual by the trails of Lower Peirce Reservoir.
The species ranges widely across East and Southeast Asia short of the Wallace Line, and a new study of Southeast Asian populations has revealed how the paleogeography of Sundaland is reflected in the birds' present distribution. Focusing on populations in southern Thailand, the Malay peninsula, Borneo, Palawan and Mindanao, the authors compared the mitochrondrial DNA of 62 specimens representing four regional subspecies. The phylogenetic analysis suggested a strong divergence (~8%) between the Mindanao birds and the other populations, whereas there was little to distinguish the peninsular and Bornean samples, both of which also showed significant signs of isolation from the Thai population.
Little spiderhunters from Borneo and peninsular Malaysia appear to have formed a single population during the last glacial maximum about 18,000-10,000 years ago, when the South China Sea shrivelled into a patchwork of savannahs and riparian forests. Physical barriers or a shift in ecological preferences probably contributed to the genetic drift between the Thai and other Sundaic populations, while much greater spans of discontinuity between Sundaland, Mindanao (which was never linked to the mainland) and Palawan (which was only intermittently connected to Borneo) have led to both phenotypic and genotypic signs of isolation. On this basis, the authors suggest a reevaluation of the subspecies complex in the light of the closeness of the Bornean and peninsular birds, as well as the distinctiveness of the southern Thai populations. A splitting of the populations in Mindanao and Palawan into fully fledged species is also recommended, a possibility that is likely to please those who seek the thrill of new lifers and vex conservationists who must add new indicators to the endemic health of islands besieged by humanity.
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