The mangrove finch is one of fifteen species of Darwin’s Finches and one of the rarest birds in the world. The species is endemic to Galapagos and although they once occupied a number of mangrove sites on Isabela and Fernandina, these tiny brown birds are now only found in two small patches of mangrove forest on Isabela, with a combined size of just 32 hectares. The birds are classified by the International Union for Conservation of Nature (IUCN) as critically endangered.
Since 2006, the multi-institutional Mangrove Finch Project has focused on increasing our understanding about the biology and ecology of these birds and the threats they face.
While the exact causes for the reduction in the mangrove finch’s range of habitat are unknown, the threats to their population are well documented, and results show that it is primarily due to species introduced to the Galapagos Islands. Invasive rats predating on eggs and chicks has been a major problem, but after much work rats are now being successfully controlled at breeding sites and fledgling success rate has increased as a result.
The introduced parasitic fly Philornis downsi also causes a very high mortality rate. Adults of this fly are harmless, but as larvae they suck the blood of nestlings, often resulting in the chicks’ death. In 2013, 37% of nestlings were killed this way and despite international efforts a safe control method has yet to be found.
Giving them a headstart…
January 2014 saw the start of an exciting new phase in the project which resulted in the team successfully raising 15 mangrove finch chicks in captivity and releasing them back into the mangroves.
Mangrove finches are the earliest breeding species of Darwin’s finch. They breed during the wet season (December to April), nesting high up in the mangroves and lay up to five clutches each year.
Breeding success is very low in the first few months of the season, partly due to predation by introduced species, but if a nest fails the adult finches will begin to renest immediately for as long as the rains continue.
The Mangrove Finch Project is working to boost the birds’ numbers by turning this into an opportunity. By collecting eggs from the first clutch and hand-rearing them at the Charles Darwin Research Station before releasing them back into the wild, the project team are able to give the chicks a head start in life.
This head-starting programme is now in its 3rd year and in February 2016, another 15 captive-reared chicks successfully fledged, another great success for the project.
During the nest collection field work in early 2016, the team also found the first wild-fledged mangrove finch to be observed in February in seven seasons. In addition, two fledglings which were captive-reared in 2014 and 2015 were observed in the wild. They could be identified by their unique coloured rings. This is very positive news for the Mangrove Finch Project as this is the first time these birds have been spotted since their release.
The team hope to continue the head-starting programme for another season, and hope that in this time we will be able to find out if the first captive-bred finches from 2014 have started to breed. Excitingly the first breeding behaviour from a head-started bird has been observed, with a 2014 head-started male heard singing. You can listen to the song, recorded by the Charles Darwin Foundation, below.