Giant Tortoise

A little different to our usual species spotlights, we're looking here at tortoises in general around the world, with a particular focus on the Aldabra Giant Tortoise and its role in rewilding in the Indian Ocean.

Full Name: Aldabra Giant Tortoise

Latin Name: Aldabrachelys gigantea

Classification: Reptile

Adult Weight: Varies with smaller species weighing just a few kilograms, while Aldabra giant tortoises can weigh up to 250 kilograms (550 pounds).

Adult Length: Varies from a few inches in smaller species to over 1.2 metres (4 feet) in Aldabra giant tortoises.

Lifespan: Tortoises often live 50–100 years, with Aldabra giant tortoises living over 150 years, making them some of the longest-living animals on Earth.

Preferred Habitat: Warm, dry habitats such as deserts, grasslands and scrublands.

Status: Varies overall, the Aldabra giant tortoise is currently listed as vulnerable by the IUCN.

Aldabra tortoises can live over 150 years, making them among the longest-living animals. © Markus Kammermann

Giant Tortoise

The giant tortoise is considered a keystone species in ecosystems where they are native, such as the Galápagos Islands. Keystone species play a critical role in maintaining the structure of an ecological community, influencing many other species and helping determine the types and numbers of other species in the ecosystem.

Giant tortoises impact their environment by dispersing seeds, which promotes plant growth and diversity. They also graze on vegetation, creating open areas that allow other plant species to thrive, and their movements shape the habitat structure. This makes their presence vital for the balance and health of their ecosystems.

Why are Tortoises Important to Rewilding?

The giant tortoise is considered a keystone species in ecosystems where they are native, such as the Galápagos Islands and many in the Indian Ocean.

The tortoise’s slow metabolism contributes to its incredible lifespan. © Gregor Mima

Past Tortoise Rewilding Efforts

The Galápagos Islands have been a focal point for rewilding efforts, particularly involving giant tortoises, which are keystone species in their ecosystems. Over the last sixty years, more than 9,000 tortoises have been bred in captivity and released into the wild to recover populations devastated by centuries of exploitation. These tortoises play a crucial role in dispersing seeds and maintaining vegetation dynamics, making their return essential for restoring the islands' ecological balance.

These gentle giants can weigh up to 250 kilograms (550 pounds). © MartinStr, Pixabay

Current & Future Tortoise Rewilding Projects

Rewilding efforts involving Aldabra giant tortoises are centred on their introduction to islands in the Indian Ocean, particularly Mauritius, where they serve as ecological proxies for extinct native species. On islands like Ile aux Aigrettes and Round Island, Aldabra tortoises have been introduced to replicate the role of the now-extinct Mauritius giant tortoise. These introductions help control invasive plant species and promote the growth of native vegetation by grazing and seed dispersal, mimicking the ecological functions of their extinct counterparts.

Looking ahead, there are plans to expand these initiatives to other islands in the region, further restoring degraded ecosystems and improving biodiversity. These rewilding projects aim to combat the effects of habitat loss and species extinction caused by human activity. Aldabra tortoises, with their resilience and ecological significance, are key players in these efforts, demonstrating how carefully planned rewilding can heal damaged ecosystems and pave the way for a more biodiverse future in the Indian Ocean.

Aldabra tortoises play a vital role in seed dispersal, helping ecosystems thrive. © Alexas_Fotos, Pixabay

The rugged shell of a tortoise is made of bone and keratin, offering strong protection. © Marzena, Pixabay

Physical Description

Tortoises are land-dwelling reptiles recognised for their sturdy shells, slow movements, and herbivorous diet. Tortoises vary in size, from small species just a few inches long to giants that grow over a metre.

The Aldabra giant tortoise (Aldabrachelys gigantea), native to the Seychelles' Aldabra Atoll, is among the largest tortoise species, with males weighing up to 250 kilograms (550 pounds). Their dark, rugged shells and long necks allow them to graze efficiently, shaping their environment and dispersing seeds. These gentle giants play a vital role in their ecosystems, making their conservation essential for maintaining biodiversity.

Aldabra tortoises are a conservation success story, with stable populations. © Alexas_Fotos, Pixabay

Tortoise Behaviour

Tortoises are generally slow-moving and solitary animals, though they occasionally gather in areas with abundant food or during breeding seasons. They are most active during the cooler parts of the day, such as mornings and late afternoons, and spend the hottest hours resting in shaded areas or burrows.

On the Aldabra Atoll, the giant tortoises are often seen in large groups grazing on open grasslands or basking in the sun. They dig shallow pits in the sand or soil to rest and regulate their body temperature. During the breeding season, males can become more active and competitive, engaging in head-bobbing displays and pushing contests to establish dominance. Despite their size and strength, Aldabra tortoises are gentle giants, contributing to their reputation as iconic symbols of island ecosystems.

What Threats do Tortoises Face?

Tortoises face a range of threats, primarily stemming from human activity. Habitat destruction due to agriculture, urbanisation, and deforestation is one of the greatest challenges, reducing the availability of food and shelter. Illegal poaching for their meat, shells, or the pet trade poses a significant risk, particularly for rare species. Invasive species, such as rats, pigs, and dogs, often prey on tortoise eggs and hatchlings, further impacting their populations. Climate change adds additional stress, altering habitats and food availability, and in some cases, increasing the risk of flooding in nesting areas.

Aldabra giant tortoises, despite being well-protected on the Aldabra Atoll, are not immune to these challenges. Rising sea levels and extreme weather events driven by climate change threaten their low-lying island habitat. Additionally, the introduction of invasive species, diseases, or increased human disturbance could jeopardise their stable population. Conservation efforts are essential to mitigate these threats and ensure their survival in the wild.

The tortoise’s slow metabolism contributes to its incredible lifespan. © Gregor Mima

Giant tortoises can consume over 25 kilograms of vegetation in a day. © Alexas_Fotos, Pixabay

What do Tortoises Eat?

Tortoises are primarily herbivorous, feeding on a variety of vegetation depending on their habitat. Their diet typically includes grasses, leafy plants, flowers, fruits, and sometimes cacti in arid regions. Some species may occasionally consume small amounts of carrion or invertebrates for additional nutrients. Tortoises are opportunistic feeders, adapting to seasonal availability and using their strong, beak-like jaws to tear through tough plant material.

Aldabra giant tortoises have a similar plant-based diet, grazing on grasses, herbs, leaves, and woody plant shoots. On the Aldabra Atoll, they are known to feed on mangroves and succulent plants, which provide moisture in their dry environment. They also play a critical role in their ecosystem by consuming fruits and dispersing seeds, which helps maintain plant diversity and regeneration.

Aldabra giant tortoises are known to dig shallow pits to cool off in the heat. © Alexas_Fotos, Pixabay

Cultural Significance

Tortoises hold deep cultural significance in many societies, symbolising longevity, wisdom, and resilience due to their long lifespans and slow, deliberate movements. In mythology and folklore, they often represent the Earth or the cosmos, as seen in the concept of the "World Turtle" in Hindu, Chinese, and Indigenous American traditions. Their steady nature has made them icons of patience and endurance, often depicted in art, literature, and proverbs.

Aldabra giant tortoises, in particular, are celebrated as living relics of prehistoric times, drawing fascination for their size and ancient lineage. They are iconic symbols of conservation success in the Seychelles, embodying efforts to preserve biodiversity and protect unique island ecosystems. Revered as gentle giants, they captivate the imagination of people worldwide and inspire ongoing conservation and rewilding projects, highlighting the importance of harmonious coexistence with nature.

Distribution of the Tortoise

Tortoises are found across the world, primarily in warm climates, including Africa, Asia, the Americas, and islands in the Indian and Pacific Oceans. They are most commonly associated with arid or semi-arid habitats such as deserts, grasslands, and savannahs, though some species inhabit forests or wetlands. Island-dwelling tortoises, like the famous Galápagos and Aldabra species, are often endemic to their specific locations.

Aldabra giant tortoises are native to the Aldabra Atoll in the Seychelles, where they thrive in the grasslands, mangroves, and coastal dunes of this isolated coral island. While their natural range is limited, conservation and rewilding efforts have introduced them to other islands in the Indian Ocean, such as Mauritius and Madagascar, to restore ecological roles once played by extinct native tortoise species.

Tortoises have excellent senses of smell, helping them locate food. © S Nagel

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