Galápagos Tortoise

## Adapting and surviving

Galápagos tortoises are the giants of the tortoise world. Males can weigh more than 500 pounds (227 kilograms), and females average about 250 pounds (113 kilograms). They have thick, sturdy legs to hold up all that weight, but they still spend a lot of time lying down to conserve energy. There are two types of Galápagos tortoises. The largest, with big, round shells, are called “domes.” The smaller kinds of tortoises have shells that curl up in front like a saddle and are called “saddlebacks.”

## A historic observation

Naturalist Charles Darwin made his historic voyage on the HMS Beagle from 1831 to 1836. When the ship sailed around the Galápagos Islands, he and his shipmates marveled at the animal life they found, from blue-footed boobies and marine iguanas to giant tortoises. One thing that caught his eye was that each of the 13 larger islands in the Galápagos Islands had a slightly different form of giant tortoise.

Each was uniquely suited for survival on that particular island’s environment. For example, domed shells were found on tortoises living in highlands with lush pastures. Saddleback shells gave the tortoises on other islands more flexibility to reach sparse vegetation found higher off the ground, allowing them to stretch their neck to eat from bushes and cactus. On islands with sparse vegetation, the tortoises have longer legs to climb a little and reach food growing up high; these tortoises tend to be smaller, possibly to help them travel through their harsher habitat.

## How about those shells?

Although they are massive animals, their shells are not solid. Instead, they are made up of honeycomb structures that enclose small air chambers. This makes it possible for the tortoise to carry the weight of the shell without much difficulty. The shell encompasses the animal’s ribs, so a tortoise cannot "walk out" of its shell, like you may see in cartoons. The lungs are located on the top of the tortoise’s body, under the top dome of the shell.

## A life of leisure

Galápagos tortoises tend to lead a peaceful, lazy life that centers on eating, relaxing in the sun, or wallowing in puddles. Because they are cold-blooded like other reptiles, they like to soak in the sun to warm up. At night, they may rest partially submerged in mud, water, or brush to keep warm during cool evenings. Mud wallows can also keep a tortoise cool during the day.

There’s nothing like a nice, slow, ambling walk if you’re a tortoise. The feet on the powerful front legs are turned inward, so each step moves the tortoise from one side to the other and never in a straight line. Tortoises rarely just stand up and walk, however; they prefer to put some weight on the front legs before pushing with the back feet and sliding forward.

## Greens are good

Galápagos tortoises are herbivores that eat prickly pear cactus (a favorite) and fruits, as well as flowers, leaves, and grasses. In fact, these tortoises can go without eating or drinking for up to a year, because they can store food and water so well. Tortoises don’t have teeth, so they use the bony outer edges of the mouth to bite off and mash food. Once in the mouth, food is quickly swallowed. They don’t have a good sense of smell, so they use their eyes to find food. Anything red really gets their attention!

At the San Diego Zoo, the tortoises are offered kale, collard, mustard and dandelion greens, bok choy, and seasonal fruits and vegetables. Galápagos tortoises can retain a great amount of water, which allows them to survive the long dry season on the islands.

## Wanna fight?

When threatened, the tortoise pulls itself into its shell with a hiss. The hissing sound is just the tortoise letting air out of its lungs. If a fight breaks out among males, the tortoises face each other with ferocious glares, open their mouth, and stretch their head as high as they can. Whoever reaches the highest wins, even if he is much smaller overall than the other male! The loser pulls his head in with a noisy hiss, and the battle is over. To us, this looks like they’re just putting on a show; but it’s a serious matter to the tortoises, especially in the wild, where fights occur over mates or a specific food item or clump of food.

## Courting tortoises

When giant tortoises reach maturity, at about 20 to 25 years of age, they begin to think about reproducing. In the wild, their breeding season is generally between January and August. After mating, the females begin a journey of several miles to reach nesting areas. They look for dry, sandy ground and dig a hole about 12 inches (30 centimeters) deep. Here they lay hard-shelled eggs the size of tennis balls and cover them up with sand.

Temperature plays a role in whether a tortoise hatchling is male or female: if the nest temperature is low, more males hatch; if it is high, more females hatch. When the young tortoises emerge from their shells, they must dig their way to the surface, which can take up to one month! It’s then up to them to survive on their own, as the mother does not stay to help them.