Galapagos Tortoise

Galapagos Tortoise

Chelonoidis nigra

The largest living species of tortoise, the Galapagos tortoise is native to seven of the Galapagos Islands. They are ectothermic (meaning cold-blooded) and spend 1-2 hours basking in the sun before spending another 8-9 hours grazing and relaxing. Throughout the 19th century, Galapagos tortoises were valued by sailors as part of their food supply; the tortoises could live for months without food or water aboard ships, making them an ideal source of fresh meat while away from shore. Single vessels would capture hundreds of them, all but exterminating the population.

During mating season, males compete by stretching out their heads and the winner is the “tallest.” This usually ends the battle, but if the loser doesn’t concede, they might bite and nip at each other. Near the end of spring’s wet season, the female will move to arid lowlands with well-defined nesting sites. To soften the ground, the female urinates on a patch of soil in an open, sunny spot. The tortoise then lays 2-20 white, hard-shelled, spherical eggs about the size of billiard balls in the hole. She lowers herself over the opening and, by sliding her underside about, raises mud to form a smooth cap almost flush with the surrounding ground. This cap hardens in the sun. The tortoise’s eggs hatch after 4-8 months. Hatchlings need rainfall to soften the mud cap so that they can dig their way out of the sealed chamber. The sex of Galapagos tortoise babies is determined by the incubation temperature of the eggs. Temperatures below 28 °C produce males and above 29.5 °C produce females.

It is impossible to determine the age of a tortoise once it has reached adult size, so the ages of many tortoises are merely estimated. The oldest known Galapagos tortoise was named Harriet, and she lived at the Australian Zoo until the age of 175. Each of the Galapagos Islands had its own unique subspecies of Galapagos Tortoise at one time; several of them are now extinct. Observations of their adaptations contributed to the development of Charles Darwin’s theory of evolution.

What are they like?

Physical Description: Galapagos tortoises have a large, bony shell (carapace) of a dull brown or gray color. The plates of the carapace are fused with the ribs in a rigid protective structure that is integral to the skeleton. The legs are large and stumpy, with dry scaly skin and hard scales. The front legs are five-clawed, and the back legs are four-clawed. The average weight of a male Galapagos tortoise is about 500 lbs, while females average around 250 lbs. The length from head to tail of males is up to 6 ft; females are generally smaller.

Life Span: In the wild, Galapagos tortoises can live for over 100 years, possibly up to 200 years. Their lifespans in zoos are the same as in the wild.

Diet: Galapagos tortoises are herbivorous grazers, eating mostly cactus and grass in the wild. At Philly Zoo, they eat a mix of produce, including apples, carrots, leafy greens, and a mix of minerals. During the summer, they receive watermelons as enrichment.

Social Structure: This species can be found in large groups. They have a dominance hierarchy based on the height to which the tortoise can stretch its head.

Habitat: Galapagos tortoises live in tropical deciduous forests, tropical scrub forests, and tropical savanna and grasslands.