Abstract

The Galapagos Islands remain the only conserved tropical archipelago in the world, with over 95% of its biodiversity intact. In fact, none of the 58 resident bird species have gone extinct, although this may soon change as a number of species are on the brink of extinction, and disease has been confirmed as a known factor in a number of population declines. In this presentation, we discuss two health studies on endemic Galapagos avian species, the Floreana mockingbird (Mimus trifasciatus) and the Galapagos hawk (Buteo galapagoensis). These two species are experiencing very different conservation challenges and exemplify how the conservation medicine approach offers a means to better understand these challenges and to develop appropriate conservation strategies for the future for these species, and other Galapagos endemics.

Introduction

The Galapagos Islands remain the only conserved tropical archipelago in the world, with over 95% of their biodiversity intact.³ In fact, none of the 58 resident bird species, of which 52% are endemic, have gone extinct; however, this may soon change as a few species are on the brink of extinction, with disease a known factor in a number of population declines. Anthropogenic changes, due to the rapidly expanding resident human population (estimated at 20,000 in 2006 up from 12,000 in 1996) and tourist population (estimated at 140,000/yr in 2006 up from 60,000 in 1996) (www.ingala.gov.ec/galapagosislands) (VIN editor: link could not be accessed on 1/11/21) are occurring in Galapagos on an unprecedented scale. Human-induced changes may be having direct and indirect impacts on the health of avifauna (and other wildlife) in Galapagos. Additionally, conservation management measures for the 97% of the archipelago which is the Galapagos National Park may themselves have impacts on the health of the avian species.

In 2000, the WildCare Institute, Saint Louis Zoo and the University of Missouri-Saint Louis created the Center for Avian Health in the Galapagos Islands, in collaboration with the Charles Darwin Foundation and Galapagos National Park, to better understand the disease threats to the avifauna of Galapagos.^5-7 In this presentation, we discuss two of our many projects: an avian health survey for the re-introduction of the Floreana mockingbird (Mimus trifasciatus) and the determination of the cause(s) of mortality in the juvenile cohort of Galapagos hawks (Buteo galapagoensis) on Santiago Island. These two endemic Galapagos species face very different conservation threats and necessitate different conservation medicine approaches.

Avian Health Survey for the Re-introduction of the Floreana Mockingbird

The Floreana mockingbird (Mimus trifasciatus), with an estimated population of 136 birds in 2007, is one of the rarest bird species in the world. The potential causes of extinction for the Floreana mockingbird include loss of genetic variation, environmental (e.g., climate change), introduced species (e.g., black rats), and diseases. Although poxvirus is the pathogen of greatest concern for the Floreana mockingbird,⁹ a number of other disease agents, including Mycoplasma gallisepticum and Philornis downsi, which are present in the archipelago, and diseases that may soon arrive (e.g., Plasmodium relictum and West Nile virus) are thought to cause morbidity and mortality in this species.

Having been extirpated from its native Galapagos island of Floreana over 125 yr ago, the remaining individuals reside on Floreana’s two small satellite islands, Champion and Gardner-by-Floreana. It is for this reason that a collaborative effort, “The Re-introduction of the Floreana Mockingbird to its Island of Origin” was initiated.² Within this plan, a top priority for phase one is to determine disease threats associated with re-introducing this species back to Floreana.

The objectives of the health component of the re-introduction plan are to 1) determine the prevalence and distribution of infectious and parasitic disease agents in domestic and wild birds on Floreana, 2) determine the prevalence and distribution of infectious and parasitic disease agents in the remnant Floreana mockingbird populations on the two satellite islets, and 3) make recommendations based on these data for how to best execute mockingbird re-introductions to Floreana. In summary, the health work has been designed to determine disease threats that may undermine the plan prior to any re-introductions.

In early 2008 we collected biomaterials from one half of the Floreana mockingbird population and a number of chickens and passerines on Floreana. Laboratory diagnostic testing will soon follow. Data on the prevalence and distribution of the infectious and parasitic agents within and between the different study populations (e.g., mockingbirds, chickens, and passerines) are one of the key data sets for making recommendations as we move forward with the re-introduction of Floreana mockingbirds back to Floreana.

Determination of the Cause(s) of Mortality of the Juvenile Cohort of Galapagos Hawks on Santiago Island

The endemic Galapagos hawk is the only hawk species in Galapagos. Currently, there are breeding populations on eight of the main islands with the two largest populations (approximately 500 hawks per island) residing on Isabela and Santiago. During our long-term population studies of the hawks on Santiago, we noted a decline in the number of juvenile hawks (1–4 yr of age) on the island in a 3-yr period from 2005 (n=160) to 2007 (n=0).⁸ Therefore, in 2008 we initiated a study to determine the cause(s) of this decline. Interestingly, the complete loss of the juvenile cohort on Santiago coincides with the completion of the largest island goat eradication campaign in the world, with approximately 100,000 goats eradicated on Santiago in the period 1996–2006.^1,4 We have focused our study on hypotheses of the possible cause(s) of mortality in this cohort. These hypotheses are that with the eradication campaign that resulted in the removal of 100,000 goats on the island, vegetation has recovered to a point in which non-territorial hawks can no longer hunt well, some other inadvertent response to the removal of goats (e.g., loss of a food source), or a direct negative impact from the methods used to eradicate the goats.

A short trip in early 2008 documented the presence of at least 60 non-territorial birds, using the same census techniques as in the 2005–2007 surveys. However, the vast majority of these were first-year birds produced during the 2007 breeding season. This suggests that whatever problem was associated with the disappearance of the juvenile class between 2006 and 2007 has not persisted, and thus the hypotheses of too much vegetation cover or loss of a food source are most likely incorrect. We recovered one set of dried hawk remains, containing skin, bones, and feathers. We currently are soliciting information on whether and how these remains can be informative to test other hypotheses regarding causes of death (e.g., toxins). It is good news that this unknown problem does not appear to have persisted, although we will continue to monitor this population through other seasonal changes.

Since Santiago represents approximately half of the world’s population of this species, we want to do everything we can to understand the cause(s) of this sudden disappearance of an entire age class and to unravel whether the island restoration project has inadvertently affected the health of the hawks on the island, or whether this represents a shift back to a more natural population level following the removal of an important food source. These data are important to obtain before similar management programs (e.g., invasive vertebrate eradication) are used on other islands.

Acknowledgments

We thank the Charles Darwin Foundation, Galapagos National Park, WildCare Institute, Saint Louis Zoo, and the University of Missouri-Saint Louis for supporting this work.

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