Imagine you’re Charles Darwin, feeling you have a pretty good handle on the earth’s amazing biodiversity after exploring for four years and filling your ship, The Beagle, with a multitude of live animal specimens for further study. Then, off the coast of Ecuador, you and your crew come upon an archipelago called the Galapagos. You realize then you most certainly haven’t seen it all! And it’s no coincidence that Galapago is an archaic word in Spanish meaning tortoise.
Greeting Darwin and his crew in 1835 were creatures such as the marine iguana, literally half of the Blue-Footed Boobies on earth engaging in mating rituals, the only flightless Cormorant species on earth, and a 3-inch painted locust that was capable of jumping ten feet in the air.
But perhaps most famous and now beloved of his discoveries were the Galapagos Giant Tortoises. They were huge, they were docile, and they were everywhere. It’s estimated that there were once 250,000 of them on the islands, and until humans discovered them, they really had no natural enemies.
The Galapagos Giant Tortoise subspecies vary slightly from island to island in the Archipelago, adapting perfectly to the different environments. The major adaptation, though, has to do with shell shape — they sport either domed or “saddle-backed” shells (with an upward angle on the front of the carapace, which restricts how far UP they can extend their long necks). It turns out that the tortoises living on more arid islands need the flexibility to reach higher up for their favorite food, the prickly pear cactus. Those living on lush, humid islands only have to extend their necks forward to nab a delicious herbivorous dinner.
The Giant Tortoises lead a placid existence in the wild, and also in human care, sleeping up to 16 hours per day, basking in the sun, and occasionally wallowing in mud. In the wild, Galapagos finches can often be found on their shells, symbiotically pecking pesky ticks from the folds of the tortoises’ skin.
During mating season, things get interesting
Things perk up a bit during mating season, between January and August (depending on weather), when males may compete for females in a curious faceoff : it’s a neck-stretching and mouth opening contest, where the one with the longest neck gets the girl! Mating can take hours, and is celebrated by the champion-necked males with an extremely loud roaring throughout.
For visitors to the Reid Park Zoo, it’s often confusing when Ferdinand and Isabella, the two Galapagos tortoises, are enjoying this ritual. Since the roaring is audible throughout the Zoo, guests flock to the lion habitat, but find them fast asleep — how can this be?
The females lay between 2 and 16 eggs about the size of tennis balls, burying them about 12 inches in the ground. Then they walk away — so the hatchlings are on their own, right from the start. The temperature in the nest will determine whether the babies will hatch as males or females. A few centuries ago, enough of these hatchlings survived to create a growing population of these long-lived giants. Nobody can verify the life span of a Galapagos Tortoise, but it has been estimated to be up to 170 years.
The Trouble Begins
Spanish explorers first discovered the tortoises in the sixteenth century, and they quickly became an important shipboard food source for seafarers, including pirates, merchantmen, whalers, and yes, the crew of The Beagle.
One of these giant tortoises’ amazing adaptations is the ability to go up to a year without food or water, making them the perfect, low-maintenance livestock onboard a ship. They also have shells which look solid, but are very light due to a honeycomb structure. And of course, they were very easy to capture, though maybe not to carry — some individuals can weigh more than 500 pounds.
Also, settlers on the islands introduced invasive species, like pigs, goats, and rats, which began to consume the same plant life that had been central to the tortoises’ survival. And of course, the tortoises were also used for food by the islands’ inhabitants.
Now they’re endangered
Originally, 14 different subspecies of the Galapagos Giant Tortoise were identified in the wild, but sadly, two of those subspecies are now believed to be extinct. Best estimates are that only 10,000–15,000 altogether now survive in the wild.
But there is reason for hope
In 1959, the Ecuadorian government established Galapagos National Park in order to protect remaining habitat, and eggs began to be collected and incubated at the Charles Darwin Research Station on Santa Cruz Island. Here at home, under the guidance of the Association of Zoos and Aquariums, Galapagos tortoise breeding programs began in accredited zoos . The aim was to reintroduce members of the species to the wild once their habitats were deemed safe. The San Diego Zoo alone has hatched more than 94 Galapagos tortoise babies through the years, enabling breeding programs to get started at other AZA zoos. It takes patience though — breeding only begins when individuals reach the age of 20–25.
Way to go, Diego
There have also been some amazing in situ success stories. A recent example is the tale of Diego, who had been living in the San Diego Zoo and was returned to the Charles Darwin Research Station to help repopulate his kind on the island of Espanola. In 1965, only 26 members of Diego’s species survived there. Since his arrival back in The Galapagos in 1976, numbers have grown to nearly 2,000. Diego gets credit for fathering roughly 40% of them, or around 800 new tortoises. Diego will now live out his years — he’s over 100, but of course that’s probably just late middle age for a Galapagos tortoise! He’ll enjoy many more serene years — back on his native island.
Darwin would approve.
Originally published at http://reidparkzooexpansion.org on June 7, 2021.