The Cocos finch or Cocos Island finch (Pinaroloxias inornata) is the only one of the Darwin's finches not native to the Galápagos Islands, and the only member of the genus Pinaroloxias. Sometimes classified in the family Emberizidae, more recent studies have shown it to belongs in the tanager family, Thraupidae. It is endemic to Cocos Island, a Pacific island which is approximately 360 miles (580 km) south of Costa Rica.
The Cocos finch was formally described in 1843 by the English ornithologist John Gould under the binomial name Cactornis inornatus.[2] The species was moved to a new genus Pinaroloxias by Richard Bowdler Sharpe in 1885.[3] The genus name combines the Ancient Greek pinaros meaning "dirty" or "squalid" with Loxia, a genus introduced by Carl Linnaeus in 1758 for the crossbills. The specific epithet inornata is Latin for "plain" or "unadorned".[4] The Cocos finch is a member of a group collectively known as Darwin's finches.[5] Although traditionally placed with the buntings and New World sparrows in the family Emberizidae,[6] molecular phylogenetic studies have shown that Darwin's finches are members of the subfamily Coerebinae within the tanager family Thraupidae.[7] The Cocos finch was first categorized to be closer to the warbler finch clade due to the similar morphology of cousin warbler finches.[8][9]
The Cocos finch shares many morphological similarities to other Darwin's finches despite having been separated from the Galapagos Islands.[10] What is unique, however, of the Cocos finch, is that they display an inter-species variation in feeding habits. The variation in foraging behaviors are hypothesized to be possible by observational learning from other Cocos finches.[10][11] These feeding specializations are independent of any morphological changes, sex and age differences, rather, they are derived from an inter-species variation found within the Cocos finch. Still, despite its variation in feeding patterns, Cocos finches are categorized as one species with no known subspecies.[11]
The Cocos finch stands at about 12 cm long weighing in at about 12.5 g. The bird has a black decurved pointed bill for eating berries and insects that are its main diet.[10][12][13] They are sexually dimorphic in that the males have almost entirely black, having black feathers from the tail, breast, nape, and crown. Unlike male finches found on the Galapágos islands, male Cocos finches have black beaks year-round, never changing color.[12][14][13]
Female Cocos finches have a lighter brown complexion compared to males. There is a black splattering of feathers on their breast area down to the flank and rump. The belly of the female Cocos finch is milky white compared to the mantle of the bird. The nape and crown area are more noticeably black.[12][15][13] The young are similar, but have yellow bills.
The call of a Cocos finch can be described as a "buzzy" like sound with a high-pitched ending note. The beginning of the call can form a “djirr” sound followed by a high pitched “tiew” sound. Calls can also include a high pitched “phzzzz” sound.[13][12]