Endangered Birds

Captive Breeding of Endangered Birds: The Mangrove Finch and Floreana Mockingbird Programs

Mangrove Finch

The Galapagos Islands have not yet experienced any vertebrate extinctions, although several species are currently considered threatened, from vulnerable to critically endangered. Two of the most endangered species are the Mangrove Finch and the Floreana Mockingbird. Both species have reached critical population sizes (about 80 for the Mangrove Finch and 140 for the Floreana Mockingbird) and have highly restricted distributions. To ensure the survival of these species, it is recommended that new breeding populations be established outside of their current limited distributions.

While translocation – capture at an existing site and release into a new one – may not be optimal for these two bird species as it involves removing breeding birds from an already undersized population and releasing them into an unsure environment, captive breeding and the subsequent release of young, bred and reared in captivity, is considered more suitable. However, the high degree of expertise required for a captive-breeding program of this kind is presently missing. Given the scarcity of both species, effective and safe captive breeding and rearing techniques must be developed before any of the endangered birds are removed from the wild populations. Therefore, the development of these techniques will involve working with similar species – in the case of the Mangrove Finch, the work will involve the Woodpecker Finch, while Galapagos Mockingbirds from Santa Cruz will be used as stand-ins for the Floreana Mockingbird.

Floreana Mockingbird

The Durrell Wildlife Conservation Trust (DWCT) is partnering with the Galapagos National Park (GNP) and the Charles Darwin Foundation (CDF) in these projects. The DWCT has achieved the conservation and survival of critically threatened birds, including passerines, in other island ecosystems (including Mauritius, St. Lucia, Montserrat, and Madagascar) and will provide assistance in the establishment of the breeding and rearing programs and in building institutional capacity in Galapagos.

Although most land birds in Galapagos are still relatively widespread, the Mangrove Finch is considered one of the rarest birds in the world. The world population of the finch is less than 100 birds. The species is restricted to mangrove forests along the west coast of Isabela (Canal Bolivar) and, historically, on the adjacent east coast of Fernandina. Mangrove forests are a scarce habitat in the arid, volcanic Galapagos Islands and the Mangrove Finch has always been one of the less abundant species. Today, Mangrove Finches exist in only two sections of coastal mangrove forests encompassing a total area of less than 1 km_ – at Playa Tortuga Negra and Caleta Black, separated by 1 km of barren lava, on the northwest coast of Isabela. Exact causes for the reduction of its range are unknown, but a variety of introduced, invasive species are considered threats. Black rats, cats, and smooth-billed anis affect nesting success; fire ants and the wasp Polistes versicolor are also potential threats. However, the most significant threat may be from parasitism by the larvae of the botfly Philornis downsi, a fly first recorded in the islands in the 1980s and most likely exotic, whose parasitism results in nestling mortality. Another potential threat is from insect-borne avian diseases, such as avian pox or malaria, but their impact is not yet clear and research is currently underway to determine potential impacts.

Parasitism by P. downsi, an obligate bird parasite (the adult fly is non-parasitic), was first identified in the Galapagos in 1997 and then at Mangrove Finch sites on Isabela in 2000. Mortality of nestlings of other species of Darwin’s finches due to parasitism has been recorded as high as 27%, with lower brood sizes suffering the highest mortality. The Mangrove Finch has a mean clutch size of only 2.25 eggs per nest.

Current research will focus on the development of effective captive breeding and rearing techniques using the Woodpecker Finch and field research on the last remaining population of Mangrove Finches, accompanied by control of the main recognized agents of decline (i.e., disease and predation). Once captive breeding and rearing techniques using the Woodpecker Finch are developed at the Charles Darwin Research Station (CDRS) on Santa Cruz, the work on the Mangrove Finch will occur in-situ, with captive breeding facilities established relatively near the existing population. Captive-bred young will then be released in areas on Isabela and Fernandina where they previously occurred in an attempt to re-establish Mangrove Finch populations throughout its historical range.

The Floreana Mockingbird is another one of the rarest birds in the world. It occurs only on two tiny islets off the coast of Floreana Island: Gardner-por-Floreana and Champion. Although the species was recorded as being common on the island of Floreana by Charles Darwin in 1835, the last specimen collected on Floreana was in 1852 and the last reported sighting there was in 1868. The mockingbird was probably extinct on Floreana by 1888, when searches for it were unsuccessful. Extinction from Floreana has been attributed to: hunting by colonists; predation by introduced dogs and/or cats; destruction by goats of one of their main nesting habitats, the cactus forest (Opuntia megasperma); or perhaps most likely, predation at the nest by introduced black rats. The estimates for the current population are: 28 birds on Champion and 149 on Gardner-por-Floreana.

Visiting the Galápagos Islands in 1835, mockingbirds (there are four species in Galapagos) were undoubtedly the inspiration behind Charles Darwin’s development of ideas that were published in 1859 in his most famous work The Origin of Species. It was indeed Darwin’s visit to Floreana and his observation of the mockingbird there that suggested to the young naturalist that species were not immutable.

Annual surveys of the two remaining islet populations began in 2003, and a program of repeatable monitoring, ringing, and genetic analysis has been established. In March 2007 an international workshop was held in Galapagos to develop strategies to ensure the survival of the islet populations and to initiate the reintroduction of mockingbirds to Floreana. The reintroduction is part of the Galapagos National Park Project Floreana, which includes the removal of all exotic mammals and the restoration of the native flora and fauna.

One key component of the project outlined at the workshop was the establishment of captive breeding facilities in order to produce a sufficient number of birds for release on Floreana. To develop and perfect the captive-breeding methodologies, work would begin with the more abundant Galapagos Mockingbird. This work would be linked with the Mangrove Finch project to reduce costs and ensure effective use of outside expertise.

Captive husbandry trials at the Charles Darwin Research Station

The aviaries at the CDRS are permanent structures and will be used in phase one of the Mangrove Finch and Floreana Mockingbird projects for husbandry trials and staff training. This work will include development of techniques and training for:

Acclimatization of captured birds (birds brought into captivity may be wild adults and/or eggs and young taken from wild nests)
Transport of adult birds
Transport of eggs and chicks
Incubation of eggs
Hand-rearing techniques
Weaning hand-reared chicks
Socializing hand-reared birds
Diet and presentation of food
Training hand-reared birds
Best social groupings in aviaries
Rearing techniques: natural and/or artificial parent
The number of eggs that can be added to an existing nest
Acceptance by parents to raise other chicks
Range of ages for introducing eggs and chicks to nests
Range of ages of chicks for hand-rearing
Fostering eggs to wild birds
Release of captive-reared birds

Best practice protocols established during trials will be transferred to breeding-release programs established in situ on Isabela (Mangrove Finch) and Floreana (Floreana Mockingbird).

Commenting is closed for this article.