Helping to Save Darwin's Finches - Control of a Parasitic Fly

The isolation of the Galapagos Islands, 600 miles out into the Pacific Ocean, has resulted in over 1,300 species of flora and fauna that are unique to the Islands.  This same isolation leaves them particularly vulnerable to introduced species which are still their greatest threat.  In recent years an invasive parasitic fly, Philornis downsi, has begun to have a devastating effect on the land birds and in particular, the finches.

 Since the introduction of Philornis downsi to the Galapagos Islands in the 1960s, this parasitic fly has spread to 14 islands in the archipelago and is known to cause morbidity and mortality in 12 species of birds.  The life cycle of Philornis downsi includes a parasitic larval stage, which feeds at night on the blood of nestling birds, and a free-living adult that lays eggs in bird nests containing young.  The larvae continue to develop in the nest as they parasitise the birds. For example, one nest of a Cactus Finch (Geospiza scandens) in March 2010 that contained a brood of four chicks had 170 larvae present, which is 42 larva per nestling.  It was no surprise when none of the nestlings survived.  In addition to direct nestling mortality, which is proven to be as much as 100%, a number of studies have confirmed that surviving nestlings often have deformed beaks, reduced growth rates, and anaemia.

In 2008, thanks to our supporters, GCT provided funding for research into the life cycle and behaviour of Philornis downsi.  Although some useful results were obtained, it proved extremely challenging to raise flies to maturity in the Charles Darwin Foundation (CDF)'s laboratories, and CDF have since begun a collaboration with SUNY College of Environmental Science and Forestry in Syracuse, New York, who send volunteers to Galapagos to build on the work begun by the CDF scientists and who continue to investigate the fly in their own laboratories.

Climatic conditions meant that 2009 was a year of low reproduction for Philornis downsi.  However in 2010, the species made a strong reproductive recovery, and the high mortality and long-term impacts on finch populations from this fly species are of grave conservation concern, especially for endangered and declining species like the Mangrove Finch (Camarhynchus heliobates) and the Medium Tree Finch (Camarhynchus pauper).  In the 2010 finch reproduction season, three visiting scientist groups documented up to 100% mortality of Small Tree Finch (Camarhynchus parvulus) and Medium Ground Finch (Geospiza fortis) nestlings on Santa Cruz island and the Medium Tree Finch nestlings on Floreana island.  Thankfully this result is not universal with more successful reproduction being recorded in Small Ground Finch (Geospiza fuliginosa) in the arid lowlands of San Cristobal island. 

Although the implications of what appears to be a near 100% loss of fledgling success may not be immediately appreciated (since adult finches are still seen) evidence suggests a shifting age structure of finch populations as the juvenile populations are not replacing older species.     

 
What action needs to be taken

Immediate management actions are necessary to control this invasive and pathogenic fly species if we are to stop the extinction of one or more Darwin finch species.  With the growing list of threats that finches and other terrestrial birds face today in Galapagos, it becomes even more imperative that management measures are implemented. Options for control may include fly trap attractants and insecticide use at a local scale; and biological control using a wasp which in turn parasitises the Philornis larvae.

Given the difficulties encountered so far in the investigation, CDF has determined that a carefully paced approach will provide the best chance of an effective outcome together with maintaining accountability to donors.  To do this, they plan to invite the top world experts in Philornis research to formulate a research strategy and recommend options for management planning, including an emergency plan in the event of imminent extinctions.  The next step is therefore to hold an international workshop that includes CDF, the Galapagos National Park, Ministry of Agriculture, current researchers working on Philornis downsi, and international experts so that CDF can 1) better coordinate research and monitoring efforts; and 2) analyse the control options.

Without immediate action the infamous finches of Galapagos are at risk of extinction.  Please help us to put the measures in place to prevent this potential tragedy from happening by donating here.