Galapagos Giant Tortoises: Synthesis of a half century of study and conservation

By: , Posted on: December 8, 2020

Galapagos Giant Tortoises provides the most comprehensive, up-to-date synthesis of information ever assembled on these iconic reptiles. This complex of 15 endemic species (Chelonoidis spp.), of which three are extinct and one yet undescribed, distributed across 8010 km2 of the larger islands and volcanoes of the Galapagos Archipelago, represents the greatest concentration of endemic species of not just tortoises but of all turtles anywhere on the planet. By the late 1800s and early 1900s, after more than two centuries of massive exploitation of Galapagos tortoises, many scientists and conservationists declared these reptiles as “given up to extinction.” The longevity of these creatures, however, ensured their survival to the era of conservation, which began in the Galapagos Islands in 1959 with the establishment of the Galapagos National Park. Over the next 60 years, scientists and natural resource managers have worked together to reverse the tortoises’ path to extinction to one leading to recovery.

Figure 1. Tortoises on Wolf Volcano

The story of Galapagos tortoises, their dispersal and evolution, their destruction and eventual recovery, is complex, with each species occupying a different and ecologically distinct island or volcano, each facing a different suite of threats, and each undergoing recovery via different means. The steady progress of tortoise conservation in Galapagos has placed most populations well on the road to recovery.

Figure 2. Galapagos National Park rangers marking an Eastern Santa Cruz tortoise for future monitoring.

Over the last two decades, knowledge of Galapagos giant tortoises has increased dramatically. A major recent impetus has been the Giant Tortoise Restoration Initiative (GTRI), launched in 2014 expressly to expand Galapagos giant tortoise conservation programs to focus on rebuilding tortoise numbers to match historical populations. The Initiative set forth a mandate to fill information gaps, which triggered new research on Galapagos giant tortoises. Researchers and conservationists came together to capture and meld their accumulated knowledge into this new volume — Galapagos Giant Tortoises –- a long-overdue synthesis that takes advantage not only of the hundreds of peer-reviewed publications on giant tortoises, but also myriad unpublished documents, including technical and field trip reports, theses, and other.

Figure 3. Giant tortoise on Santa Fe Island.

The book begins with an overview of the place of Galapagos giant tortoises within the world of turtles and tortoises. This is followed by an in-depth look at human-tortoise interactions, beginning with human perceptions of Galapagos tortoises through history, then an in-depth analysis of the era of exploitation, the visit of Charles Darwin in 1835 and the subsequent importance of giant tortoises in the development of his theory of evolution by natural selection, and finally the era of collectors and the beginnings of scientific inquiry.

The natural history of Galapagos tortoises is covered in 10 chapters, many of which present previously unpublished results. These chapters cover: evolution and phylogenetics; morphology; reproduction; thermoregulation; diet, behavior, and activity patterns; population biology; movement ecology; tortoise habitats; the role of giant tortoises in island ecosystems; and giant tortoises in a changing climate.

Figure 4. Juvenile Española Tortoises released on Santa Fe Island.

The remainder of the book documents tortoise conservation, which began in earnest in the 1960s. Beginning with search and rescue, followed by an ever-growing tortoise breeding and repatriation program, control and eradication of invasive mammals that impact tortoises, the eventual incorporation of tortoise genetics into tortoise conservation strategies, and an increased focus on tortoise health in both captive and wild populations, nearly all tortoise populations are now on a strong trajectory toward full recovery. Species replacement programs are also underway or being planned for those species that went extinct due to human activity.

To delve more deeply into conservation strategies, four chapters present case studies of individual populations, each restored via a different strategy determined by the specifics of each situation. These case studies describe the island, the decline of the endemic tortoise population, the conservation actions used to restore both the tortoise population and the island, and the outcomes. One of the greatest conservation successes in Galapagos is that of the Española giant tortoise (C. Hoodensis), rescued from the brink of extinction in the 1960s when just 15 individuals survived. The nearly self-sustaining population of some 2500 individuals has resulted in the closing of the restoration program in 2020, marking the end of one of the most successful endangered species recovery programs in the world.

Figure 5. Pinzón Island adult tortoise.

The second case study presents the story of the Pinzón Island tortoise population. Although 100-200 adult tortoises survived to the era of conservation, since the late 1800s, no tortoise hatchlings survived due to predation by introduced black rats. Collecting eggs and hatchlings in the wild, rearing them in captivity until large enough to be “rat proof,” and then repatriating them, the population grew steadily.  In 2012, black rats were eradicated and young tortoises are once again being recruited into the population in situ. This tortoise population has also reached a level of sustainability.

The other two case studies focus on three islands where the endemic tortoise species went extinct: Floreana, Pinta, and Santa Fe. In the case of Floreana and Pinta tortoises, efforts to partially “de-extinct” the species are underway following the discovery of tortoises with mixed ancestry on Wolf Volcano on northern Isabela Island, including some with partial Floreana tortoise ancestry and fewer with partial Pinta tortoise ancestry.  The restoration of a tortoise population on Santa Fe Island began in 2015, using the Española tortoise (C. Hoodensis) as a replacement species or “conservation introduction” for the extinct Santa Fe tortoise. The goal of this project is to restore not only a tortoise population but also the ecosystem services once provided by the original tortoise species.

Figure 6. Tortoise center on Isabela Island.

The combination of the massive exploitation of tortoises over past centuries and the tortoises’ extended generation times— about 30 years—means that rebuilding populations will require a few to several centuries to reach their original numbers and distribution, but they are now well on the path to complete recovery. And although the future is full of uncertainty, given a changing climate, the ever-present threat of new invasive species and especially introduction of new tortoise diseases, and intensifying pressures from animal traffickers, the habitat base for Galapagos giant tortoises remains extensive and largely secure. Tortoise population growth is slow but steady. The book’s last chapter looks ahead 200 to 300 years in the future and presents an overarching vision of the islands and their tortoises as one of thriving populations and recovered ecosystems on all islands and volcanoes where tortoises once roamed. 

Ready to read the book?

Galapagos Giant Tortoises brings together researchers and conservationists to share the most up-to-date knowledge of Galapagos giant tortoises. This book documents the history, the pressing conservation issues, and success stories recovering several of the 15 different species of Galapagos tortoises from near extinction. Buy your copy now on the bookstore and save 30% + get free shipping when you use promo code STC30.

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Agricultural and Biological Sciences


Agricultural and Biological Sciences


Agricultural and Biological Sciences