The Indris (Indri indri) is the most arboreal of all the lemurs and hardly ever comes down to the ground. It is the biggest of all living lemurs with a head and body nearly a metre long, and its legs are even longer in proportion than those of a Sifaka, the big toes are widely separated from the rest and about twice the length, so that each foot resembles a huge calliper with which the animal can grasp thick trunks. Indris also use scent in marking the trees, though to a much lesser extent than the lemurs. Instead territories are established using their voices. Every morning and evening, a family fills its patch of forest with an unearthly wailing chorus.