Efforts to reintroduce Española Galapagos giant tortoises to their native Española Island have been a success, according to recent research. In the 1960s, the tortoises, a critically endangered species, had been over-hunted and displaced by invasive species. Just 15 of these lumbering giants remained alive. So in 1963, scientists captured all of those survivors to keep them safe and to try to breed them. Over the years, the tortoises did indeed breed, and in the meantime, the Galapagos National Park Service undertook a massive feral goat eradication campaign. Goats first invaded the island in the late 19th century, and those voracious animals quickly ate up much of the native vegetation. With the goat problem under control, the scientists could gradually begin to reintroduce the tortoises. Now, the goats are gone, and around 1,000 tortoises live on the island. Researchers report that they're successfully breeding on their own. "It's a rare example of how biologists and managers can collaborate to recover a species from the brink of extinction," the authors of the new assessment said in a statement. The restoration job is far from finished, however. According to the researchers, much of the island is still covered in shrubby, woody underbrush, which took over after the hungry goats were extirpated. Those types of aggressive pioneer plants prevent other species, such as the native arboreal prickly pear cactus, from growing. But tortoises need the cactus, which forms a major part of their diet. So until the island's flora can be restored to something resembling pre-goat times, the tortoise's population will probably plateau at about the levels it's at now. "Population restoration is one thing but ecological restoration is going to take a lot longer," the researchers said.