Adaptive Evolution in the Jamaican Blackbird Nesopsar nigerrimus

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Abstract
The Jamaican blackbird N. nigerrimus (Osburn) is confined to the moist montane regions of Jamaica where it is found primarily above 515 m. It forages for animal food among bromeliads, clumps of dead leaves, moss-covered trunks and branches and tree ferns. Nesopsar''s feeding habit probably evolved on the island in the absence of species of Dendrocolaptidae and Furnariidae specialized for arboreal rummaging. Compared with other icterids, Nesopsar has shorter legs and more curved claws, which are advantageous in arboreal (trunk) foraging. Nesopsar has a proportionately longer and narrower bill than all the other icterids examined, enabling it to probe more efficiently into crevices, cracks and epiphytes. The muscle for lowering the lower mandible, M. [muscularis] depressor mandibulae, and the muscle for elevating the upper mandible, M. protractor quadrati, are not ordinarily strong muscles in birds. Both of these muscles have become very strong in the icterids, in association with the gaping method of feeding. In Nesopsar, the gaping function aids in prying underneath loose bark, dead branches, accumulation of plant materials and bromeliads.

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