Animal Spotlight: Galapagos Tortoise

Taxonomy:

gettyimages-71452408-e
Lonesome George, who was the last giant tortoise on Pinta Island. Photo By: Rodrigo Buendia
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Testudines
  • Family: Testudinidae
  • Genus: Chelonoidis
  • Species: nigra*

*Recently, the subspecies were declared to be their own species. There are many species of the Galapagos tortoise based on their island origin

  • Average Length: 4 ft (1.2 m)
  • Average Weight: 475 lbs (215 kg)
  • Lifespan: 100+ years

The giant tortoises of the Galapagos are among the most famous of the unique fauna of the Islands. While giant tortoises once thrived on most of the continents of the world, the Galapagos tortoises now represent one of the remaining two groups of giant tortoises in the entire world, the other living on Aldabra Atoll in the Indian Ocean.

It is believed that the first tortoises arrived to Galapagos in the eastern Pacific Ocean 2-3 million years ago by drifting 600 miles from the South American coast on vegetation rafts or on their own. They were already large animals before arriving to the islands, colonizing the eastern-most islands of Española and San Cristóbal first. They then dispersed throughout the archipelago, eventually establishing at least 14 separate populations on ten of the largest Galapagos Islands (Española, Fernandina, Floreana, Pinta, Pinzón, San Cristóbal, Santa Cruz, Santa Fe and Santiago). They are also native to the five major volcanoes on Isabela Island (Wolf, Darwin, Alcedo, Sierra Negra and Cerro Azul). Tortoises are now extinct on Fernandina (due to volcanism), Floreana, and Santa Fe (both due to exploitation). They are also extinct on Pinta Island, after Lonesome George’s death.

Physical Description:

GEOCHELONE ELEPHANTOPUSThis giant reptile is the largest living tortoise, with relatively heavy limbs, a long neck, and a heavy carapace, the shell, the can reach lengths of up to 150 centimeters (59 inches). The different species illustrate the principle of ‘adaptive radiation,’ where populations isolated on islands or on parts of larger islands within the island chain have adapted to different conditions and now have distinct appearances.

The subspecies can be generally separated into those with ‘domed’ shells, which occur on the larger, wetter islands, and smaller tortoises with ‘saddleback’ carapaces that are found on smaller islands with dry vegetation. It is thought that the distinctive saddleback shell of some populations of the Galapagos giant tortoise enables its bearer to reach taller vegetation, with these tortoises also having longer limbs and necks.  The domed tortoises tend to be much larger in size and live on islands with humid highlands where forage is generally abundant and easily available. Saddle-backed shelled tortoises evolved on the arid islands in response to the lack of available food during drought. The front of the carapace angles upward, allowing the tortoise to extend its head higher to reach the higher vegetation, such as cactus pads.

Tortoises don’t have teeth. Instead, they use the bony outer edges of the mouth to bite off and mash food. Once in the mouth, food is quickly swallowed. They also don’t have a good sense of smell, so they use their eyes to find food.

Diet:

giant tortoise.PNGGalapagos tortoises are herbivorous, feeding primarily on cactus pads, grasses, and native fruit. Their favorite is the prickly pear cactus and fruits and they will also eat flowers, leaves, and grasses.

These tortoises can go without eating or drinking for up to a year, because they can store food and water so well. They will drink large quantities of water when available and store in their bladders.

Behavior:

Giant tortoises lead a simple life, grazing on grass, leaves, and cactus, basking in the sun, and napping an average of 16 hours a day. Their activity is driven by ambient temperature and food availability. In the cool season, they are active at midday, sleeping in the morning and early afternoon. In the hot season, their active period is early morning and late afternoon, while during midday they are either resting and keeping cool under the shade of a bush or half-submerged in muddy wallows.

Tortoises have several ways of communicating with each other. The only known vocalization in Galapagos tortoises is the sound that males make when mating. Females make no vocalizations at all. Instead, they communicate through their behavior.  Like many other species, they have ways of conveying dominance and defending themselves. Competing tortoises will stand tall, facing each other with mouths open and stretching their necks up as high as possible. Usually, the highest head wins, while the loser retreats submissively into the brush.

Tortoises breed primarily during the hot season between January and August. Females will then migrate to nesting zones several miles away to lay their eggs. They can lay from 1-4 nests of 2 to 16 eggs over a single nesting season. The eggs are laid in dry, sandy ground about 12 inches (30 centimeters) deep. After incubating from 110 to 175 days, the eggs hatch. The young hatchlings remain in the nest for a few weeks before emerging out of a small hole adjacent to the nest cap. They will not mature until they reach 20 to 25 years of age.

giant-tortoise-2
San Diego Zoo

Conservation and Threat:

Currently, there are only 11 species of giant tortoises left on the islands, down from the 15 when Darwin arrived. Hunted as food by pirates, whalers, and merchantmen from 17th-19th century, more than 100,000 tortoises are estimated to have been killed off. They were captured and stored live on ships as a source of meat.

Nonnative species continue to be a threat to their food supply and eggs. Feral dogs, cats, and rats eat juvenile tortoises before their carapace has fully developed, while goats and cattle compete with the giant tortoises for vegetation. Today, only about 15,000 remain.

They are listed on CITES Appendix I and classified as ‘vulnerable’ by IUCN. Their CITES listing prevents international trade of the species.

In 1959, the Galapagos National Park and the Charles Darwin Foundation was established, which is responsible for the systematic review of the status of all tortoise populations. They have been running a highly successful tortoise-restoration program since the 1970s, raising hatchlings from eggs until they are robust enough to be released into the wild without falling victim to predation. One of their major achievements has been to increase the population of the critically endangered Hood Island tortoise, which numbered just 13 individuals in the 1970s but now has over 1,000 members in the wild.

galapagos-tortoise-pictures

The only thing saving several of the populations was the longevity of tortoises, keeping some old adults alive until conservation efforts could save their species.

Interesting Facts:

  • The Galapagos Islands were named for their abundant giant tortoises.
  • The Spanish word for tortoise is galápago, which means saddle, a term early explorers used for the tortoises due to the shape of their shells.
  • The Galapagos giant tortoise is one of the longest-lived of all vertebrates. The oldest recorded individual reached the impressive age of 171
  • When threatened, the tortoise pulls itself into its shell with a his. The hissing sound is just the tortoise letting air out of its lung.
  • The Galapagos Archipelago became the first UNESCO World Heritage Site
  • The Pinta Island had a single known tortoise, Lonesome George, who lived up until June of 2012 at the Tortoise Center on Santa Cruz where he spent the last 40 years of his life. George’s remains are being preserved and will go on display permanently in Galapagos in 2014.
  • On some islands, Galapagos finches clean parasites from the skin of the tortoise, with the tortoise raising itself up on its legs to facilitate the process.

References + For More Reading

Giant Tortoises

Galápagos Tortoise

Galapagos giant tortoise (Chelonoidis nigra)

Long-Extinct Galápagos Tortoise Species May Be On Its Way Back

Galapagos Conservation

Galápagos giant tortoise

SDZ: Galapagos Tortoise

Baby Tortoises Found On Galapagos Island For First Time In Over 100 Years

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s