Once you get by the sharks on Aldabra -- which can take a while -- you get to the tortoises. These fellows (and gals) are all over the place. As noted earlier, an estimated 100,000 of these giants call Aldabra home. That's five times as many as in the entire Galapagos archipelago.
Tortoises definitely have personalities (tortoisalities?). Some pull back into their shells if you approach. Some hold out their heads and hiss. And some stick out their heads and wait to be petted.
We didn't witness it, but apparently there's a behavior in which the Aldabra Rail (the only remaining flightless land bird in the Indian Ocean) will knock on the trailing edge of a tortoise's shell and, in response, the tortoise will extend its neck and legs so that the rail can pull off insects. Some researchers on the island use that technique to get tortoises to relax when they approach.
Tortoises are the largest critters on the island, so they fill many of the ecological niches that mammals hold in other areas. They even do their best to be giraffes.