The Cocos finch or Cocos Island finch is the only one of the Darwin's finches not native to the Galápagos Islands, and the only member of the genusPinaroloxias. 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, which is approximately south of Costa Rica. It is a chunky 12 cm long finch, weighing around 12.5 g and with a black decurved pointed bill. The male is entirely black, while the female is a heavily streaked brown, with a paler underside. The young are similar but have yellow bills. The standard clutch is two brown-spotted white eggs, which are hatched in a roughly spherical nest built at the end of a tree branch.
Taxonomy
The species name of the Cocos finch, Inornata, meaning plain or unadorned in Latin, was coined by Augustus Addison Gould in 1843. The genus of the Cocos finch would later be verified by Richard Bowlder Sharpe in 1885. The Cocos finch was originally placed in the family Emperizidae but recent phylogenic studies shows that diversification of the Cocos finch originates in the family Thraupidae. The Cocos finch was first categorized to be closer to the warbler finchclade due to the similar morphology of cousin warbler finches. Although, there has been evidence claiming that the Cocos finch belongs closer to the tree finches due to its phylogenic studies via mtDNA sequence matching closely to related birds of the tree finch clade. The Cocos finch shares many morphological similarities to other Darwin's finches despite having been separated from the Galapagos Islands. 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. 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.
Description
The Cocos finch stands at about 12 cm long weighing in at about 12.5 g. The bird has a small pointed beak for eating berries and insects that are its main diet. They are sexually dimorphic in that the males have black feathers from the tail, breast, nape, and crown. Unlike male finches found in Galapagos island, male Cocos finches have black beaks year-round. Female Cocos finch have a lighter brown complexion compared to a male Cocos finch. 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. 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.
Distribution and Habitat
The Cocos finch is exclusively found in Cocos Island, 580 km SE from Costa Rica. Cocos finches are not known to have traveled outside of Cocos Island making its habitat and reproduction range to only be at 30 km2 within the island. The habitat of the Cocos finch is mostly within Hibiscus thickets, closed-canopy forest and woodland forest. The climate within Cocos Island is described to be a typical rain forest climate with high humidity and chances for rainfall. The island has a varied landscape with bodies of lakes, streams, and caves and is home to other species including endemic lizards, small mice, small cats, and some migratory birds.
Cocos finches known to be a generalist species, although they are also known to specialize in an individual level which can result in different foraging behaviors within individual Cocos finches. This specialized behavior of Cocos finches can be explained through learning foraging patterns through other Cocos finches and can resonate said individual behavior to other Cocos Finches.
Breeding
Cocos finch usually nest throughout the year; however, their breeding season falls usually at around January–February. They form a nest using lichen and dry moss as their main material. Eggs are in clutch sizes of about 4–5 with a distinctive pink/light brown spots.
Threats
Cocos finches face mammalian predatory encounters including native and introduced rats and cats in the island. Despite its predators, there is no evidence of high predatory pressures on the Cocos finches themselves. Scientists conclude that due to the low predatory pressures on Cocos finches, they have developed this specialized feeding behavior to evolve to a more generalist species.
Status
Cocos Island is a natural reserved island and that there is limited human interaction towards the Cocos finch and to other Cocos Island inhabitants. While there has been increasing tourism around the island, there is no evidence of high disturbance rates from these tourists to affect the wildlife in the island including the Cocos Finch. While the predation and disturbance rate of Cocos finch are low along with a steady population rate, the IUCNdeems the Cocos finch to be vulnerable due to the small habitat it occupies; about 30 km2 of the whole Cocos Island. As of now, there are about 6,000-15,000 Cocos Finches living isolated in Cocos Island.
