The neck of the Aldabra giant tortoise is very long, even for its great size, which helps the animal to exploit tree branches up to a meter from the ground as a food source.

[10] Females are generally smaller than males, with average specimens measuring 91 cm (36 in) in carapace length and weighing 159 kg (351 lb).

[6] A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Aldabrachelys: The subspecific name, daudinii, is in honor of French zoologist François Marie Daudin.

[16] Genetic evidence suggests that A. gigantea is most closely related to the extinct giant tortoise Aldabrachelys abrupta from Madagascar, from which it is estimaged to have diverged from approximately 4.5 million years ago.

The tortoises exploit many different kinds of habitat, including grasslands, low scrub, mangrove swamps, and coastal dunes.

Primarily herbivores, Aldabra giant tortoises eat grasses, leaves, woody plant stems, and fruit.

In 2020, a female Aldabra giant tortoise on Fregate Island was observed hunting and eating a juvenile lesser noddy, indicating that the species was in the process of learning to catch birds.

Those living in an environment with food available higher above the ground have more flattened top shells with the front raised to allow the neck to extend upward freely.

[citation needed] As the Aldabra giant tortoise is primarily herbivorous it spends much of its time browsing for food in its surrounding well-vegetated environment.

They dig wallows, hide under shade trees or in small caves, as well as submerge themselves in pools to keep cool during the heat of the day.

Some individual Aldabra giant tortoises are thought to be over 200 years of age, but this is difficult to verify because they tend to outlive their human observers.

Mating takes place between February and May, and in July-September[26] females lay between 9 and 25 hard-shelled eggs in a 30 cm deep nest.

[29][30] A reference genome and low-coverage sequencing analyses has looked at revealing within- and among-island genetic differentiation within the Aldabra population, as well as assigning likely origins for zoo-housed individuals.