Darwin’s finches are a group of birds composed of fourteen different species, in which all but one are found on the Galapagos. They are iconic to researchers for their classic display of evolution. These birds have been studied for a long time, and we have record of the changes and divergences of their species traits. Unfortunately, two of these treasured species, the mangrove finch and the medium tree finch, are now listed by the International Union for Conservation of Nature (IUCN) as critically endangered. Many other populations are facing decline.
The major reason for their decline is a parasitic fly called Philornis downsi. The fly is typically found in Trinidad , Brazil, and is predicted to be found in other countries of South America. It was introduced to the Galapagos Islands in the 1960s, but it was not worried about until the 1990’s were they have been a problem ever since.
It is the larvae of Philornis downsi that are the cause for the concern. The harmless adult female fly will lay her eggs in the nests just as chicks are beginning to hatch. The fly eggs will hatch, and the larvae will crawl into the nasal cavities of the chicks where they will eat away at nasal cavity. Three days later, the larvae will move to the bottom of the nest and hide during the day. They wait until nighttime to feed on the hatchling’s blood. Nests infested with the parasite often do not live (between 60-100 larvae can be found in a nest alone). Those that do are deformed and have a tough time eating due to deformities of the beak. It is particularly devastating, because Darwin’s finches depend on the beak variation to survive in the habitats. Their beaks are formed to specialize in specific niches in their unique habitats.
Click picture for more information on Mangrove Finches (Camarhynchus heliobates)
The fate of the birds currently does not look good. Some of the species have become extinct locally on at least one island they previously inhabited. The warbler finch seems to have vanished from the island of Florena. The mangrove finch originally inhabited the islands of Fernandia and Isabela is now only found on a small portion of Isabela. Their population is estimated to be around eighty individuals. The current outlook for the species is not helped due to the fact that only twenty chick hatched this breeding season. Nearly a third of the chicks did not survive. Philornis downsi parasitism has been blamed for their deaths.
Researchers are calling for a need to control the fly’s spread. The parasite attacks finch fledgling reducing the mortality rate of the population. The birds do face other factors including habitat degradation, disease, and predation from other introduced species. The specific threat of the parasite seems to have a determining factor. Being that no bird species has gone extinct from the Galapagos Islands since humans reached the them in the mid-sixteenth century, the loss of these birds out be a blow to the fragile ecosystem of famous place.
Click picture for more information about the Medium Tree Finch (Camarhynchus pauper).
Plans and proposals exist, but each have their own problems and rewards. First, Scientists from the Charles Darwin Foundation, San Diego Zoo, and the Galapagos National Park Directorate are planning to remove mangrove finch chicks from the island in early 2014 to try to raise the chicks in incubators. (Other project: IUNC Mangrove Finch efforts) Also, last year, a workshop was held on the Santa Cruz Island to develop methods to control the fly, but funding and difficulties with trying to raise the fly in captivity have halted efforts. Proposals for biocontrol with a parasitic wasp and using chemicals, but there are too many questions about long term effects. A final proposal is to let nature takes its course and evolution to act. Adult finches have been recorded eating the larvae, therefore reducing the numbers of parasites in their nest.