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July 31, 2015
A mangrove finch released in the wild.
In April of this year, we reported that eight captive-reared mangrove finch chicks were being prepared for release into their natural habitat on Isabela Island. The project team recently returned from their extended stay in the mangrove forest of Playa Tortuga Negra, and they have reported that the release and subsequent monitoring of the chicks was a success.
The mangrove finch (Camarhynchus heliobates), the rarest of “Darwin´s Finches”, has an estimated population size of less than 100 individuals — with fewer than 20 breeding pairs remaining. Research shows that the introduced parasitic fly, Philornis downsi, is one of the primary causes of high nestling mortality, with up to 95% mortality of nestlings.
The release followed the collection of eggs from Playa Tortuga Negra in February and the subsequent hand-rearing of eight fledglings at the Charles Darwin Research Station’s (CDRS) rearing facility on Santa Cruz Island. During their release, the fledglings were placed in the pre-release aviary located inside the mangrove forest at Playa Tortuga Negra, where they spent three weeks adapting to their natural habitat. Several food sources, including the natural food of the mangrove finch and supplementary passerine pellet food, were placed inside the aviary.
A finch searches for food after its release in the wild.
After three weeks, the aviary was opened and the finches were free to come and go at will. The project team continued to provide food inside the aviary for any birds that returned, and daily observations were made to record any birds visiting the aviary. Over time, fewer individuals returned as they adapted to being in the wild.
Tiny transmitters were placed at the base of the birds’ tail feathers to facilitate short-term monitoring of the finches; long-term individual finch identification will be possible through colored rings placed on the legs of each individual. Post-release telemetry monitoring showed the dispersion of most juveniles within the mangrove forest at Playa Tortuga Negra, with some individuals found north towards Caleta Black and southward in the arid zone as far as the west side of Darwin Volcano and Tagus Cove.
CDF volunteer Joel Alava monitors released finches.
In addition to the release activities, eleven wild nests from ten finch pairs were monitored at Playa Tortuga Negra, revealing that some pairs nested five or six times without producing fledglings while five pairs were successful and produced a total of six fledglings. Parasitism of P. downsi was the major cause of chick mortality — and parasites were present in all monitored nests, including those that had fledged.
According to Francesca Cunninghame, project leader for the Mangrove Finch Captive Rearing Program:
“Releasing and monitoring eight mangrove finches bred in captivity, as they adapt to their natural habitat, is incredibly rewarding. Unfortunately, 2015 was a much more challenging year compared with our first attempt in 2014 and we have released fewer finches than hoped. However, eight young birds, released back into the wild once safe from the threat of P. downsi is a significant boost to the juvenile population, and from previous research we know that none of them would have survived as chicks in the wild.”
The release and consequent monitoring successfully completed the final stage of the 2015 captive rearing program that began in February, and the results are positive for the mangrove finch population. Although the work to date represents just a small step towards the long term conservation of the species, we remain committed to prevent the extinction of this unique species.
The Mangrove Finch Captive Rearing Program is a bi-institutional project carried out by the Charles Darwin Foundation and the Galapagos National Park Directorate representing the Ministry of Environment, with the collaboration of San Diego Zoo Global and Durrell Wildlife Conservation Trust.
The project is supported by Galapagos Conservation Trust, Mohamed Bin Zayed Species Conservation Fund, Durrell Wildlife Conservation Trust, International Community Foundation (with a grant awarded by The Leona M. and Harry B. Helmsley Charitable Trust), Galapagos Conservancy, and the British Embassy in Ecuador.
Reprinted with permission from the Charles Darwin Foundation. All photos © F. Cunninghame.