By guest author and GC Adjunct Scientist Dr. James Gibbs of the State University of New York’s College of Environmental Science and Forestry (SUNY-ESF).
Mating tortoises! Well, sort of. As we arrived at our study area in the middle of Santa Fe Island to check on the status of the 396 tortoises released since 2015, the very first tortoises I spotted were an ambitious pair of 7- or 8-year-old juveniles perched on a flat rock in that most awkward of tortoise postures. The small male teetered on the back of the small female; they reminded me of two tiny cars that just had a fender-bender. But these young juveniles are still way too small to “make this work.” In fact, they have another 8+ years before they arrive at the 20-year threshold when we know that Española tortoises, and probably all of the saddleback species, can start producing eggs. Although not yet ready for the real thing, their shell margins are starting to flare out and their saddles starting to peak – like the shells of their Española tortoise parents.
Over our week on the island, we saw lots of tortoises out and about. This was a bit of a surprise, as Santa Fe Island had been very dry for many months. We expected to find the tortoises hunkered down, waiting out the drought. It was so dry that the Galapagos National Park Directorate even postponed the long-scheduled release of the third cohort of tortoises to repopulate Santa Fe Island until rains arrive and the island “greens up.”
Despite the lack of rain, there seemed to be plenty to eat, at least for young tortoises adapted to life on an arid island. Their most important food source during this dry period: the quarter million massive cactus trees that call Santa Fe home. Cactus pads were scattered about – green and plump, some with bites but many with nary a scratch. Even the many land iguanas lying about seemed to have had their fill. Although very dry, with all that juicy cactus, their situation was by no means desperate.
We also found the remains of two expired tortoises. These were the first “muertos” we’ve encountered among the nearly 400 released over the last three years. The two we found dead were small and their condition (missing limbs and heads) suggested that hungry hawks, many of which patrol Santa Fe Island, were the perpetrators. Most of the tortoises released are large enough to be “hawk-proof,” but apparently not all. Nonetheless, we expected a much higher mortality of released tortoises based on what has transpired in releases on other dry islands, so the program remains overwhelmingly successful.
On our last night, after our seventh straight 11-hour day in the blazing sun, we hunkered down in our camp, stars sparkling above, while we shivered in the dark and cold of the evening, rehashing quietly all we had accomplished. Then the yawns started and we all retired to our tents. Our sleep, however, included an occasional battle with the voracious rice rats, endemic to Santa Fe. These coffee-colored critters were driven to extinction elsewhere in Galapagos by introduced black rats, but a few species still thrive – on Santa Fe, Fernandina, and a very small population on Santiago.
A study in the 1970s estimated the Santa Fe rice rat population at 10,000-100,000 – that’s a lot of incisors. In my oft-interrupted semi-sleep, it seemed there were surely at least that many right around my tent! Throughout the night, the steady symphony of snoring men was occasionally interrupted by episodic thrashing sounds, man versus rat, in a sometimes-futile attempt to keep our rodent neighbors on their proper side of the thin nylon tent walls.
Packing up in the morning to return to the shore to get picked up, I discovered my much beloved backpack, which I had carefully hung from a cactus limb — upside down, empty, and presumably safe — had five, grapefruit-sized holes, a result of nights of chewing by some curious rice rats. I hoped to get my gear down the hill in my new, well-ventilated, “swiss-cheese pack,” with nothing falling out through the holes. Then, maybe, it could be patched and used again next year when we return to continue monitoring how well this remarkable “re-tortoising” of Santa Fe Island is going. Thank you GC members. Your generous contributions to the GTRI make this important work restoring Santa Fe Island possible.
Dr. James Gibbs is Professor of Vertebrate Conservation Biology and Associate Chair of the Department of Environmental and Forest Biology at the State University of New York (SUNY-ESF).
He has partnered with Galapagos Conservancy for many years in efforts to restore giant tortoise populations in Galapagos through the Giant Tortoise Restoration Initiative, and is a frequent guest contributor to the GC blog.
All photos © GTRI.
Read more about the restoration of Santa Fe Island.