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.
The Galápagos tortoise is a large reptile that can easily survive for a year or more without food or water so why would a 600-pound, giant tortoise migrate seasonally up and down the lava-covered volcanoes of the Galápagos Islands?
Why is it that only adult turtles migrate? And why do tortoises on some islands travel very little throughout the year? How do these migrations affect the health, stress and fitness of the tortoises? How does the health of a tortoise affect its migration? Is migration a better strategy than remaining sedentary?
Researchers Seek Answers
In 2009, Dr. Stephen Blake of the Max Planck Institute for Ornithology and adjunct researcher at the Saint Louis Zoo, with his collaborators at the Galapagos National Park Service and the Charles Darwin Foundation, set out to answer these questions.
In 2013, the Saint Louis Zoo Institute for Conservation Medicine joined the project as a co-investigator with the Washington University Institute for School Partnership and State University of New York College of Environmental Science and Forestry. Their research was supported by a grant from the National Science Foundation.
Answering the above questions is critical to understanding the biology of the famous, but poorly studied, Galápagos tortoises, which may be a useful model for the study of animal migration in other species. Multiple closely related species with differing movement strategies across varying environments are rarely in a controlled geographical setting.
10-Year Tags Reveal Movement Patterns
To date, over 70 giant tortoises have been tagged with GPS devices that record the location of each tortoise every hour. The tags record the orientation of the tortoises every five minutes, providing activity records. Data from the tags is downloaded when the tortoises are found every one to six months.
The tags' 10-year battery life allows researchers to observe movement patterns over sufficient time to quantify the effect of environmental variability on movement. The tagged tortoises are located on three of the Galápagos Islands: Santa Cruz, Isabela (Alcedo), and Espanola. Preliminary data indicate movement up and down the volcanoes follows seasonal and spatial changes in vegetation productivity.
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.
Health Assessments Begin
In 2013, with the inclusion of a health component to the project, each tagged tortoise receives a visual physical exam, and blood and fecal samples are collected. Fecal samples are tested for parasites and levels of corticosterone, a hormone used as an indicator of stress. Blood samples are analyzed for baseline blood parameters to help determine an individual’s overall health. Ultrasound technology determines the presence of follicles and/or eggs to assess the reproductive status of females. This information helps researchers better understand overall tortoise health and how migration affects the health and reproduction of individuals.
This research project's strong outreach program is focused on translating research results into something meaningful for the local communities and policy makers. The program focuses on getting local young people to experience giant tortoises first-hand and learn about their ecology. Local youth from the Galápagos tortoise project are exchanging information with students working on the St. Louis Box Turtle Project about the habits of their respective tortoises. So far, more than 400 students have participated in the program through classroom and field activities.