Mangrovesirkku

The mangrove finch mainly feeds upon adult insects, grubs and spiders, which are obtained by foraging through the leaf litter, or by using its powerful beak to prise off bark from dead wood. As an alternative, particularly when food is scarce, this species employs a more ingenious method of feeding. Like the woodpecker finch (Camarhynchus pallidus), this species is known to use cactus spines and twigs to prise out inaccessible grubs from tree hollows and cavities (2). The mangrove finch normally breeds throughout the hot, wet season, commencing in December or January and lasting until May (5). Darwin's finches usually form monogamous, lifelong breeding pairs, although mate changes and breeding with more than one partner have also been observed. Generally a clutch of three eggs is laid, which are incubated by the female for about twelve days, and the young brooded for a further two weeks before leaving the nest (3).

For over a decade, the Charles Darwin Foundation (CDF) has been working to conserve the mangrove finch (2). At present, extensive research is being conducted to better understand this species' breeding biology and to determine the causes of its decline (2) (5). In the meantime, active protection of the remaining breeding populations is being employed through predator and nest parasite control (5). Despite these measures, the mangrove finch remains extremely vulnerable due to its limited range. In order to address this, the CDF and the Durrell Wildlife Conservation Trust are currently working together towards a captive breeding and translocation programme. If successful, their efforts will help to ensure a future for this remarkable species (5) (7).

Poised on the brink of extinction, the diminutive mangrove finch is not only the most endangered of Darwin's finches, but is also one of the rarest birds worldwide (3) (4). Like the other twelve species of Darwin's finches endemic to the Galapagos Islands, this species has evolved a specialised beak shape, enabling it to exploit a particular habitat and diet (3). In the case of the mangrove finch, the beak is long and pointed, with a down-curved culmen, enabling this species to lift scales of tree bark, and pick off insect prey (2). Plumage is dull brownish above, becoming olive on the rump, while the underparts are whitish with faint streaking (2) (5). Males can be distinguished by the black colouration that develops on the head and neck over the course of several annual moults (5) (6).

The mangrove finch has highly specific habitat requirements, and will only occupy dense mangrove swamps that are separated from the sea, where a large amount of leaf litter and dead wood is able to accumulate, instead of being carried away by currents (5).

Historically, the mangrove finch was known to occupy at least six mangrove patches on the islands of Fernandina and Isabela in the Galapagos Archipelago. Today, however, this species is extinct on Fernandina, and breeding populations are only recorded at two locations on the north-west coast of Isabela (5).

Classified as Critically Endangered (CR) on the IUCN Red List (1).

With a declining population of less than 100 adult birds (3) and a breeding range of around one square kilometre (5), the mangrove finch's situation is critical. The exact cause of this species' decline is unclear, but, natural factors such as the El Niño cycle, introduced species, and human activities may all be involved (2). As a result of introduced predators such as black rats, cats and the smooth-billed ani preying on eggs and chicks, and high levels of nest infestation by the blood sucking parasite, Philornis downsi, causing the death of nestlings, the mangrove finch's breeding success is low (2). Concerted conservation action is necessary if this species is to be saved from extinction.