Landbird Conservation & Control of 'Philornis downsi'
Landbird Conservation and Control of the Parasitic Fly, Philornis downsi
Charles Darwin Foundation, Galapagos National Park Directorate, SUNY-ESF, Sabine Tebbich (University of Vienna)
Medium ground finch © Giovanni Sonsini.
- In 2012, the Charles Darwin Foundation and the Galapagos National Park Directorate published the Landbird Conservation Plan: Strategies for Reversing the Decline of Passerine Birds on the Galapagos, which identified priority research areas.
- A recent assessment of the landbirds of Galapagos on the IUCN Red List indicated that 14 of the 28 small native or endemic landbirds (passerines, cuckoos and doves) are threatened with extinction, an important step in prioritizing landbird research and conservation management.
- From 2014-2016, 36 Mangrove Finch fledglings, reared in captivity, were released back into their native habitat on northwestern Isabela Island (fewer than 20 fledglings were produced in the wild during those years) as part of an ongoing effort to rebuild the population.
- Estimates of the Floreana Mockingbird population in 2010-2012 (now found only on two satellite islands off the coast of Floreana Island) range from 435 to 696. Monitoring the population over time to detect any decreasing trends is vital until the population can be reestablished on Floreana Island.
- The Least Vermilion Flycatcher, known only from San Cristóbal Island, was classified as a separate species (Pyrocephalus dubius) in 2016. Unfortunately, it has not been observed on the island since 2008 and is presumed extinct.
- The extinction of the Vegetarian Finch on Floreana Island was determined in 2018. Six small landbird species are now extinct on Floreana and at least five are in decline from a total of 17 species.
- Research in 2018 discovered that the endangered Galapagos Martin is a host of P. downsi.
Knowledge of Galapagos landbirds, including population size, health, and breeding success, has never been complete. In recent years, populations of several species — including the mangrove finch, vermilion flycatcher, woodpecker finch, and small, medium, and large tree finches — have declined on some islands. Some have gone extinct.
The reasons for these declines are not completely understood, although the biggest threat to landbirds is the invasive fly, Philornis downsi. This parasitic fly feeds on the blood of nestlings, resulting in high levels of fledgling mortality. Other reasons for these population declines may include:
- Potential competition with the introduced smooth-billed ani;
- Predation by anis and introduced mammals, such as rats and cats;
- Habitat changes; and
- Diseases such as avian pox.
To reverse the decline of small landbirds as quickly as possible, the Galapagos National Park Directorate (GNPD) and the Charles Darwin Foundation (CDF) — with the support of Galapagos Conservancy — are investigating multiple options simultaneously to protect these iconic species. Two international working groups, formed in 2012, developed strategic action plans identifying priority research for the conservation of landbirds and the control of Philornis.
The long-term goals are to:
- Permanently reduce the impact of Philornis downsi;
- Prevent further extinctions of species or populations of landbirds, and
- Restore terrestrial bird populations that are in decline to closer to their historical numbers.
As of 2018, the landbird group continues to be led by Dr. Birgit Fessl, and the Philornis group is led by Dr. Charlotte Causton, both of the Charles Darwin Foundation. Both working groups meet every two years to reassess the progress of the two action plans, identify additional research topics, and agree on a priority research agenda.
Landbird research includes evaluating the status of Galapagos landbird species, especially on the human-inhabited islands of Santa Cruz, Isabela, San Cristóbal, and Floreana, and developing strategies to detect and respond to species declines in a timely manner. Studies on the ecology of little-known species are also being carried out. The goal is to develop plans for protecting the most threatened landbird species in the Islands.
The mangrove finch (Camarhynchus heliobates) is the bird species most threatened by extinction in the Galapagos Islands. It is classified as Critically Endangered on the International Union for the Conservation of Nature’s (IUCN) Red List of Threatened Species, as fewer than 100 mangrove finches remain. The entire world population lives in two large mangrove forests on the northwestern coast of Isabela Island. As with other landbirds, the primary threat to the mangrove finch is the invasive avian parasite Philornis downsi. In 2014, researchers from the Charles Darwin Foundation (CDF) and the San Diego Zoo Global (SDZG) implemented a captive rearing program for mangrove finches, which will be continued for several years, with the long-term goal of restoring the population.
In 2018, Galapagos Conservancy funded research on the vermilion flycatcher, carried out by Dr. Sabine Tebbich of the University of Vienna, Austria. Recently, two subspecies of the Galapagos vermilion flycatcher were elevated to full species status. Unfortunately, the Least Vermilion Flycatcher, found only on San Cristóbal Island, has not been recorded since 2008, and is believed to be the first modern extinction of a Galapagos bird species. The Little Vermilion Flycatcher, originally found on eight islands, has recently gone extinct on Floreana and is threatened with extinction on Santa Cruz. The populations on uninhabited islands appear to be healthy and have recovered on islands where rats were controlled. Experiments suggest that vermilion flycatchers are better able to withstand parasitism by P. downsi, when food quality is high, and food is abundant.
Dr. Tebbich has focused her research on three populations of vermilion flycatcher (VF):
- The highlands of Santa Cruz, where less than 40 VF territories remain;
- The slopes of Sierra Negra Volcano on southern Isabela, an agricultural area with about 60 VF territories, and
- The more pristine Alcedo Volcano, with a dense VF population.
Philornis downsi is a blood-feeding, parasitic fly that was accidentally introduced to Galapagos (first discovered there in 1997), most likely from mainland Ecuador. It causes high levels of mortality in several species of endemic birds, including the critically endangered medium ground finch and mangrove finch. Mortality is caused by blood loss to nestlings, and the presence of Philornis in a nest often results in 100% mortality of nestlings.
As of 2017, the Philornis working group included 21 institutions from 9 countries. The group is focused on studying the biology of P. downsi and developing methods to control it.
Research projects focus on three areas:
- Successful captive rearing of Philornis downsi to produce a sufficient number for research.
- Development and implementation of stop-gap measures to protect endangered birds, including the use of insecticides and repellants, use of attractants (pheromones and food and nest odors) that could be used to control the fly (being developed at SUNY-ESF; GC provided the start-up funding for this research); and use of the sterile insect technique, among others.
- Biological control using natural enemies.
Galapagos Report 2015-16: Biodiversity & Ecosystem Restoration section, see:
- Galapagos landbirds (passerines, cuckoos, and doves): Status, threats, and knowledge gaps – Fessl et al. – pages 149-160.
- Long-term conservation management to save the Critically Endangered mangrove finch (Camarhynchus heliobates) – Cunninghame et al. – pages 161-168.
Photo credits, from top: Captive-reared mangrove finch hatchling © Juan Carlos Avila/CDF; adult mangrove finch © Francesca Cunninghame/CDF; vermilion flycatcher © Robert Ondrovic; deceased nestling from P. downi © CDF.