Researchers Seek Migration Answers

Animal migration has fascinated humans for centuries and is responsible for some of the most spectacular wildlife sights on Earth. Despite its ecological and cultural importance, the science behind migration remains poorly understood. If Galápagos tortoises can easily survive for a year or more without food or water, why would adult tortoises migrate seasonally up and down the lava-covered volcanoes of the Galápagos Islands in search of food?

How, when and where do Galápagos tortoises migrate? Why do tortoises on some islands travel very little throughout the year? What factors disrupt movement, and what resources are critical for survival? How do these migrations affect the health, stress and fitness of the tortoises? How does the health of a tortoise affect its movement? Is migration a better strategy than remaining sedentary? These are just a few of the questions Dr. Stephen Blake and his collaborators at the Galápagos National Park Service and the Charles Darwin Foundation set out to answer back in 2009.

Since then, researchers have been conducting cutting-edge applied science on three islands: Santa Cruz, Isabela (Alcedo) and San Cristobal. To understand tortoise migration, GPS tags are attached to the shell. The data collected are downloaded every one to six months when researchers track down the tortoises. Since 2011, over 100 giant tortoises have been fitted with a GPS tag, with each tag able to gather data for 10 years!

Although Galápagos tortoises may be famous, they are, to date, poorly understood, as is animal migration in general. Therefore, understanding the biology and migration of these giant tortoises may prove to be a useful model for the study of animal migration in other species.

Integrating Health Studies

In 2013, staff of the Institute for Conservation Medicine joined the project as co-investigators, and the project was expanded to include research on the health of the giant tortoises.

To understand health in relation to migration and ecology, each tagged tortoise receives an annual physical exam, which includes the collection of blood and fecal samples. Fecal samples are tested for parasites and levels of corticosterone, a hormone used as an indicator of stress. Blood samples are analyzed for infectious diseases and antibiotic resistance. Reproductive health is also evaluated using ultrasound technology. All this information helps researchers determine how human activities such as farming, use of antibiotics, pollution and waste management may affect tortoise health, and ultimately the health of its ecosystems. By 2020, more than 600 individuals from multiple species of tortoises across four islands have received physical exams and been tested for pathogens.

What Do We Know?

With 10 years of tracking data, researchers have been able to observe movement patterns and how environmental changes affect migration. Our findings indicate that movement up and down the volcanic slopes follows seasonal changes in vegetation. On Santa Cruz Island, the tortoises stay in the highlands during the dry season when humidity is high and green plants are available. Once the rainy season begins, the lowlands “green up,” and tortoises migrate down the volcano in search of nutritious new vegetation growth. We also discovered that tortoises actually integrate environmental conditions into their decisions about movement and migration.

By studying tortoises on privately owned land and tortoises in remote areas of the islands, we now know more about the health of the tortoises and the relationship they have with humans. Preliminary data from these health studies show that giant tortoises have been exposed to infectious disease-causing agents. Tortoises from human-inhabited islands such as Santa Cruz also have been exposed to antibiotics as shown by the presence of antibiotic-resistance genes in their feces, most likely acquired from living near farming activities.

Why Do We Care?

The Galápagos Islands are almost 3,000 miles away from St. Louis. So why do we study tortoises in Galápagos? When Charles Darwin visited the islands in 1835, there were 15 species of Galápagos tortoises roaming the islands. Compare that to today, where five of those species are now extinct with all of the remaining species endangered or critically endangered.

This is a big deal! Giant tortoises have been on this Earth for millions of years. Such long-lived animals as these may act as sentinels, meaning they could provide us with a warning if a harmful agent, like infectious disease, is present in the environment. They provide essential environmental services and loads of information about the health of the ecosystems they call home. They also serve as a keystone species, which means other species depend on them, and if they were to vanish, the ecosystem would change drastically. There is no better example of why a One Health approach - which considers animal, human and environmental health - is critical to protecting these giant tortoises.

If we can better understand these tortoise species and what makes them so unique, then we can better protect these gentle giants.

Education & Outreach

A critically important part of the GTMEP is outreach and education. Staff from all partner institutions work with local schools in Galápagos, the U.S. and the U.K. to provide authentic STEM programming, allowing hundreds of students to participate in field activities or in-class learning about the giant tortoises and threats to their survival. There’s no better way to ensure a future for Galápagos tortoises and all wildlife than by empowering the next generation of conservation leaders.

Looking Forward

To see the many publications on this work, click here. We have many more questions and seek answers; stay tuned for more studies and stories we will have to share.

Partners

Galápagos National Park
Charles Darwin Foundation
Houston Zoo
Galápagos Conservation Trust
St. Louis University Department of Biology
Saint Louis Zoo WildCare Institute