Floreana mockingbird  (Mimus trifasciatus)

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

Three species of mockingbird, each occupying different islands in the Galapagos archipelago, had a greater early influence on Darwin’s theory of Natural Selection than any other animal or plant (3). Darwin discovered the mockingbirds in 1835, whilst exploring the islands aboard the Beagle, but within 50 years of his visit, the once ubiquitous Floreana mockingbird had disappeared from the island of Floreana (2) (3) (4). Since then, this small, brown passerine has been clinging to survival on two small islets (2) (3) (5). Arguably less remarkable in appearance than it is in historical importance, the Floreana mockingbird has dark-brownish grey upperparts and dull white underparts, with distinct dark patches on the sides of its breast. Its eyes are reddish-brown and its beak is long and curved (2) (5).

Endemic to the Galapagos, the Floreana mockingbird is confined to the islets of Gardner-by-Floreana and Champion, adjacent to Floreana Island (2) (3) (5). It has the smallest available range of the four species of mockingbird occurring in the archipelago (3).

The Floreana mockingbird is often found amongst Opuntia cacti but also inhabits other stands of vegetation (2) (5) (6).

Not only do the nectar, pollen and fruit of Opuntia cacti provide an important source of food for the Floreana mockingbird, but the branching pads commonly support this species’ nests (5). Nonetheless, it does also spend considerable time foraging on the ground and in other types of vegetation for alternative sources of food, including insects, other fruits and berries, the eggs of iguanas and seabirds, and carrion (2) (7) (8) (9).

The Floreana mockingbird is a cooperative breeder, with young birds helping adults to rear offspring before eventually breeding themselves (2) (3) (10). Although these territorial groups generally range in size from two to ten individuals (11), usually they comprise only one or two pairs that actually breed (3).

With only 20 to 50 individuals left on Champion islet and an estimated 300 to 500 on Gardner (as of 2009), the Floreana mockingbird is one of the rarest and most threatened birds in the world (11). Its original extinction from Floreana was probably a combination of several factors, including the introduction of black rats (Rattus rattus) and the loss of Opuntia habitat brought about by invasive herbivores (2) (3) (5). In contrast, declines recorded in the two remaining satellite populations in some years are thought to be being primarily driven by an increase in the frequency of dry La Niña years, which lead to high levels of adult mortality (2) (5) (12). Due to its isolation since the extinction of the main population on Floreana Island, the Champion population has lost a significant amount of genetic diversity, and, given its precariously small size, is in a severely vulnerable state (2) (11). Fortunately, the population on Gardner still contains a higher number of individuals and relatively high levels of genetic diversity (11). However, a single extreme weather event or newly introduced predators could easily decimate the entire surviving population. This is not to mention the ever present spectre of an avian disease spreading to the mockingbird population, or the introduction of the black rat from neighbouring Floreana (2) (5) (11).

In 2008, the Charles Darwin Foundation, in collaboration with several other international organisations, set out an emergency management plan to preserve the imperilled Floreana mockingbird by reintroducing it to its original home on Floreana. This bold scheme is expected to be carried out in phases over a period of approximately ten years. The initial phase will involve eradicating all introduced species from Floreana and developing a program to breed mockingbirds in captivity. This will be followed by the first release trials of wild or captive bred birds and finally the supervision and monitoring of the released population (11) (12). It is hoped that the first phases of the reintroduction will be started in 2009, the bicentenary of the birth of Charles Darwin (12) (13).

To keep up to date with the conservation of the Floreana mockingbird see:

• The Charles Darwin Foundation:
  www.darwinfoundation.org
• Galapagos Conservation Trust:
  www.gct.org

For more information on this and other bird species please see:

• BirdLife International:
  http://www.birdlife.org