The green warbler-finch (Certhidea olivacea) is a species of bird, one of Darwin's finches in the tanager family Thraupidae. Sometimes classified in the family Emberizidae, more recent studies have shown it to belong in the tanager family.
When Darwin collected it in 1835 during the Beagle survey expedition he mistakenly thought it was a wren, but on return to England he was informed in March 1837 by the ornithologist John Gould that the bird was in the group of finches.[1]
It is endemic to the Galápagos Islands, Ecuador.This species is closely related to the grey warbler-finch, and were formerly considered conspecific, but both species differ in appearance, distribution, habitat, and song. Holding a distinctive place in the evolutionary history of Galápagos finches, phylogenetic studies suggest that the warbler finches represent one of the earliest branches in the radiation of Galápagos finches, diverging prior to the more well-known ground finches and tree finches. With its slender, pointed beak adapted for capturing insects, the Green Warbler Finch occupies a unique ecological niche within the Galápagos archipelago. As such, the Warbler Finches serve as a crucial species for understanding the evolutionary processes that have shaped the remarkable avian diversity found in this iconic ecosystem.[2]
The average size of Green Warbler Finches is 10 cm, and their weight can range from 8-12 grams. Green Warbler Finches have a greenish coloration to blend into their lusher semi-humid forest habitats, as well as distinctive reddish throat patches on breeding males. The upper half of the adult is typically more sandy-brown which differs from the female as they have a more olive-brown upper half.[3]
The Green Warbler Finch can use its sharp beak to gain access to different foods. Their diet consists mainly of fruits, insects, and small fruits. Some insects they eat include caterpillars, beetles, and ants, as well as spiders. They tend to eat more insects during the summer and more seeds, fruits, and berries during the winter months.[4] The Green Warbler Finch tends to forage for food in small groups or alone.[5]
The green warbler-finch consists of only one subspecies, the nominate olivacea, from Santiago, Rábida, Pinzón, Isabela, Fernandina, and Santa Cruz. Its natural habitats are subtropical or tropical dry forests, subtropical or tropical moist montane forests, and subtropical or tropical dry shrubland. They are most typically found on larger islands, most abundant in places that are humid and have higher elevation, and less abundant at places with low elevation and dry.
The Green Warbler-Finch exhibits monogamous behavior often forming long-term bonds and defends a small territory. Typically breeding during the hot wet season when bugs are plentiful. The male constructs a spherical nest using dry grasses, moss, and lichens, placing it on small branches. The female will then lay approximately 3 to 5 white eggs with reddish brown spots and incubate them alone for about 12 days. The young birds leave the nest only two weeks after hatching, contributing to the species' reproductive success.[6]
The status of the Green-Warbler Finch currently is that they are vulnerable. This status is due to the bird population decreasing due to invasive plant species and habitat loss from humans. This is shown from survey periods that measured the abundance of these birds, the first being between 2008-2010 and the second between 1997-1998 in Santa Cruz, showing a 46% decrease in the bird's population.
Conservation acts that help Green Warbler Finches are the Galapagos National Park which is home to some of these birds as well as a monitoring program for all the birds on the Galapagos Islands to keep the birds from going extinct.[7]