The story of our experiments at Makauwahi Cave Reserve in Hawai`i using large sulcata tortoises as an ecological replacement for Kauai’s extinct giant ducks and geese appeared in the first issue of The Tortoise (available in PDF here). In the ensuing months, we have expanded to eleven tortoises, including some African Leopard Tortoises (Stigmochelys pardalis). Thanks to help from interns and volunteers, we have also had the chance to collect and analyze a wealth of data concerning food choices and other ecological factors.

Interns Marie Maile McKenzie and Ron O’Brien from the University of Hawaii-Hilo carried out behavioral sampling, feeding trials, and soil studies. Their large data sets showed that sulcata and pardalis tortoises greatly prefer to eat non-native weeds over native Hawaiian species, and that their feces improve worn-out tropical agricultural soils.

Soil fertility was measured immediately outside and inside the tortoise enclosures, and the results showed consistently much richer soils inside.

UH-Hilo Professor Jim Juvik helps our interns to “wire up” a tortoise with high-tech devices to measure its activity patterns. (photo by David Burney)

Through our program to provide career training for unemployed Native Hawaiians, sponsored by the state’s Office of Hawaiian Affairs, we have been able to build more and better fences for our expanding herd, which now maintains about half our native plant restorations on the 17 acre Reserve. Our visitation is up from this time last year, as thousands of tourists, residents, and students, from kindergarten to post-doc, visit and participate in the Reserve’s many offerings. Besides our cave tours, archaeological field schools, native plant restorations, and Polynesian traditional agricultural pondfields, visitors now also can admire our beautiful tortoises and learn about extinct and invasive species, plant-animal interactions, and rewilding. The in-flight magazine of Hawaiian Airlines, Hana Hou! ran a feature article recently about our tortoise project, so interest has “taken off.”

The idea of adopting exotic tortoises — pets that outgrew their owners — to control invasive weeds, while encouraging our native plants, has worked so splendidly here on Kaua`i that we plan to further extend our fenced areas to give more tortoises a chance to do more conservation work.

Fig. 2. Our tortoise “ weed controllers” are fond of eating some of Hawai`i’s most hated weeds. (photo by Alec Burney)