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).
Our field visit to Española Island in late June 2017 marked our fifth and final annual visit to track three important GC-supported projects related to restoring the island: tortoise effects on vegetation, response of nesting waved albatross to clearing of woody plants, and trends in the cactus population.
As we backpacked up the rocky trail to our camp in the interior of the island, located underneath a massive “caco” tree (Erythrina velutina) — the only one we know for sure to exist on the entire island – we were struck by the hyper-abundance of Darwin’s finches. Huge numbers exploded from the brush where they were well-hidden from owls. As many as 50 finches could be seen at a time festooning nearby shrubs. This has been a wet year and plant growth was profuse, as were caterpillars, nectar, pollen, and soft seeds — all good finch food. But “crunch time” will soon come — in a few months the plants will die back and there will be little to eat. Many of these finches will expire in the dry season. Some will survive to reproduce — evolution in action.
The first days we focused on the tortoise exclosures — large fenced areas established to exclude tortoises. Comparing vegetation inside these areas and in established open plots, we can determine the effect tortoises have on the vegetation. This year the differences inside and outside the fences were obvious. A long wet season resulted in profuse plant growth in the absence of tortoises. Outside there was a decided shift toward grasses and away from other herbaceous and woody plants. Tortoises are an important agent of change in the ecosystems in which they live.
We then made two difficult day-long treks to the interior nesting zone of waved albatross on the south side of the island. Our counts of the many nesting albatross and eggs revealed a modest but positive increase in numbers following the creation of large clearings to allow albatross to land and take off. Counts where no clearings were made haven’t changed much. These are long-lived birds that are likely faithful to their nesting areas. We’ll come back again in five years to check again but so far it does seem some level of clearing will help these birds.
Remarkably, on the long treks over the last five years to the southern side of the island, we have found more and more tortoise sign (droppings, trails) and, this year, tortoises. Clearly tortoises are expanding slowly to other parts of the island from their initial release sites and primary living area at the top of the island. We even found one of the oldest-looking tortoises I’ve ever seen on Española — under a large cactus (one of the few adult cacti on the south side of the island). He had a hugely flared shell, was in extraordinarily good condition, and had no biologist-made markings of any kind. He regarded us with a sort of bewilderment and did not retreat into his shell — clearly a tortoise with little experience with humans. After long debate we concluded he may well be one of the original surviving Española natives. The species has been restored to about a thousand from the fourteen that remained on the island (and that one male found in the San Diego Zoo). This male might well be another original survivor. Who knows? Española still keeps it secrets.
On the last days of this expedition we focused on cactus. They are fascinating, beautiful plants, and the future of the tortoises depends to a great extent on the health of cactus populations — critical tortoise food. There is a weird mix of very young and very old cacti on Española Island. The goats seemed to have killed all cactus regeneration during their 70-to-80-year tenure. Tortoises seem to be aiding cactus reproduction through seed dispersal. Will the younger generation of cactus catch up? Or should we intervene? With 500 cacti now tagged, we can measure growth over time to help answer that question and provide guidance to the Park.
A crew from the Charles Darwin Research Station joined us on this trip (as part of the Galapagos Verde project overseen by botanist Patricia Jaramillo). They planted some 50 young cactus, each with its own small water supply and protection from the tortoises — a small experiment to determine if it is even possible to “jumpstart” cactus in the field.
On the final night of our weeklong expedition after so much exertion, I settled in for a deep sleep. In the dark quiet of the cool pre-dawn, I perceived a faint wheedling sound like an animal breathing nearby. I dismissed it and went back to sleep. Suddenly there was a crushing pressure on my head like my skull was going to pop. The entire tent began to implode. I quickly realized this was no nightmare; it was in fact a tortoise. Apparently curious if my tent was edible, she had lifted herself up and lurched forward onto my head, with nothing but the nylon tent wall between us. I wrestled her off, unzipped the tent, and poked my head out. We had “some words” in the pre-dawn darkness before she ambled off.
After recovering the tent and gathering my things, I, along with the rest of the crew began the descent to the coast, teetering under our heavy backpacks. Another field trip to Española Island was over. We returned to town with a great deal of new data to help make sense of what is happening with tortoises, cactus, and vegetation — all to help guide the Park in its long-term conservation management. And, as always, we have many stories to tell.
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.