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Tuesday 26 March 2019

What’s so special about tortoises? Let us count the ways

Facts and fables about our favourite reptile

By Ella Hill

Tortoises are descended from the dinosaurs 

This is more or less true. The earliest known ancestor of the tortoise lived among the sea-monsters of the Triassic period. These creatures eventually evolved into the turtles, tortoises and terrapins we would recognise today. The “body plan” of modern tortoises, with squat limbs and a strong shell, was laid down in the early Jurassic period, about 200 million years ago. It has proved so efficient that it has altered very little since. Relatives of the tortoise even survived the Ice Age.

They are cold-blooded 

Like other reptiles, tortoises are cold-blooded creatures but they enjoy sunbathing and will often spend part of the morning basking in the sun’s rays. The warmth from the sun raises their blood temperature, speeding up their metabolism and making them more active.

They are vegetarians (mostly) 

Tortoises mainly eat green, leafy plants and vegetables. They are also keen on fruit. In the wild, tortoises will occasionally nibble on the carcasses of dead animals, but they don’t need a lot of protein or fat.

Some can live for a year without food

Tortoises inhabit every continent except Antarctica. Different species have adapted to some extremely harsh environments, from blazing hot deserts to cold and windswept steppes. In these conditions, food is not always abundant, so a slow metabolism is an advantage.

The tortoise’s ability to fast could have led to their success in colonising remote islands like the Galápagos and the Seychelles. Scientists believe that the giant tortoises of the Galápagos probably got there by floating for weeks on end from mainland South America.

Yes. They are slow

Tortoises never evolved to move quickly. They don’t have to run from anything because the tortoise has two excellent defence mechanisms against predators, a hard carapace (shell to you and me) and an ability to retract its limbs and head.

Nor do they have to chase anything. A plant-based diet negates the need for running. Tortoises will make a beeline for a particularly appealing buttercup or strawberry, but they’ll take their time over it.

The fastest tortoise in the world as far as we know is a leopard tortoise called Bertie, from County Durham. He can travel at a maximum speed of 0.28 metres per second.

Hibernation isn’t for all

Some do, some don’t. European tortoises hibernate in the winter when there is less sunlight. Tortoises from tropical climes do not. In captivity, they need to be kept warm all year round. The same goes for desert-dwelling tortoises, although in their natural habitat they might spend some of the hot summer months sleeping underground in burrows.

Tortoises under the law

Fourteen species of tortoise have protected status in the EU. It is illegal to sell wild-caught tortoises from these species. To sell one of these tortoises in the UK, or their eggs, they must be captive-bred and you need a licence from the Department of Environment, Food and Rural Affairs (Defra).

Tortoises and eggs

Depending on the species, a female tortoise will lay somewhere between five and 30 eggs. Once her eggs have been fertilised, a tortoise can carry them for as little as one month and as much as three years.

When she is ready to lay, a tortoise builds a nest in which she will bury her eggs. The hatchlings emerge around two to three months later.

Tortoises don’t take care of their young

They generally don’t guard their nests and they don’t play any part in feeding or protecting their hatchlings. From their first outing in the world, tortoises have to be independent to survive.

They can live for a century

Some tortoises are longer lived than others. Adult tortoises can survive for anything between 40 and 150 years, depending on the breed.

The oldest tortoise ever recorded by humans, a radiated tortoise called Tui Malila and said to have been given to the Tongan royal family by Captain Cook in the 1770s, lived to the age of 188.

They are cleverer than you might think

Because tortoises are slow of gait, the modern assumption is that they are also slow of wit. But in traditional stories from around the world, tortoises are often smart. In Yoruba folklore in Nigeria, the tortoise is a wily trickster. In China, it’s a symbol of longevity and determination. And in the famous fable, Aesop’s tortoise had the nous to beat the hare.

Scientists are only just learning about tortoise cognition but they’re turning out to be cleverer than we thought. Anna Wilkinson, a professor at the University of Lincoln, studies how these reptiles think. She has tested tortoises’ cognitive mapping skills in a maze, experimenting to see how they respond to other tortoises and teaching them how to use a touch screen (they’re better at it than dogs). “We really haven’t found things they can’t do, but they don’t always do them in the way that you expect,” she says.

Further reading:

 

Illustrations by Edith Pritchett