Deadly Parasites Infect Darwin's Famous Finches

CAMBRIDGE, UK, November 11, 2002 (ENS) - Darwin's finches, made famous by Charles Darwin's theory of evolution, are facing a new threat. Parasitic fly larvae are feeding on nestling birds in Ecuador's Galapagos islands, BirdLife International is warning. BirdLife International is a global alliance of national conservation organizations of which the Ecuadorian Ornithological Foundation is a partner.

BirdLife International wrote Friday to the Ecuadorian Environment Minister Lourdes Luque alerting the government to this new threat to Darwin's finches. The conservation organization is asking that Ecuador prioritize research into the impact of the new parasites and consider improving biosecurity measures to help prevent further accidental introductions of exotic parasitic insects to the Galapagos archipelago.


Medium ground-finch Geospiza fortis (Photo John Croxall/BirdLife International)
In his book "Origin of Species" Charles Darwin cited the variety of finch species in the Galapagos as an example of adaptive radiation. He theorized that each evolved from a common ancestor species having adapted to the different ecological niches available. It is from this famous example that they became known as Darwin's finches.

Of the 13 species of Darwin's finches, seven were studied by Birgit Fessl and Sabine Tebich, who wrote the study "Philornis downsi - a recently discovered parasite on the Galapagos archipelago - a threat for Darwin's finches," published in the latest issue of the avian journal "Ibis" published in July 2002.

Fessl and Tebich report on nesting success and nestling mortality of 12 native and introduced bird species affected by the flies' parasitic larvae. All of the seven species of Darwin's finches studied were found to have the new parasitic fly larvae in their nests.

On the Galapagos island of Santa Cruz the researchers found that 97 percent of the endemic finch nests studied were infected by the fly ectoparasite Philornis downsi. They found an average of more than 23 parasites per nestling and a relatively high nestling mortality of 27 percent.

Although the researchers say it is difficult to be certain that parasites caused nestling deaths, malnutrition did not appear to be a factor, and infestation may have severely weakened nestlings because birds with holes in the back, neck and under the wings were discovered.

At least three species of fly known from South America are believed to have been accidentally introduced in food imports from mainland Ecuador. The first was identified in 1997.

"The potential impact of the newly discovered parasites may be major, and further study of the scale of the threat is urgently required," says Fessl of the Konrad Lorenz Institute.

BirdLife International's Dr. Nigel Collar, author of "Threatened Birds of the Americas," says a decline in nestling survival due to these new parasitic fly larvae would severely threaten with extinction one finch species that is already listed as critically endangered.


Mangrove finch Camarhynchus heliobates (Photo Andy Swash/WildGuides courtesy BirdLife International)
"Most worrying is the presence of these new parasites on Isabella Island, the only place in the world where the critically endangered mangrove finch Camarhynchus heliobates occurs. This is the most threatened of the Darwin's finches and numbers 110 individual birds in the wild," says Dr. Collar.

Although parasites that have evolved a host-parasite relationship often do not seriously harm their host populations, Dr. Collar explains, those brought into parasite free populations may cause severe harm before defense mechanisms evolve. Some have caused avian extinctions.

"For example, in the Hawaiian Islands, USA, the accidental introduction of the mosquito Culex pipiens fatigans in the 19th century, a vector for avian malaria, led to the extinction of several endemic bird species, including the Kaua'a 'O'o Moho braccatus, 'Akialoa Akialoa obscura, and Hawai'i Mamo Drepanis pacifica," said Dr. Collar.

More recently in Asia, the white-rumped vulture Gyps bengalensis, slender-billed vulture Gyps tenuirostris and Indian vulture Gyps indicus have declined by over 90 percent since 1994, and are now classified as critically endangered on the IUCN Red List of Globally Threatened Species. Bird experts believe these declines are linked to an as yet unidentified disease.

BirdLife International is a global alliance of national conservation organizations working in more than 100 countries who, together, are the leading authority on the status of birds, their habitats and the issues and problems affecting bird life.

The alliance is the official listing authority for birds for the IUCN-World Conservation Union Red List.