From the smallest lemurs to the largest, from nocturnal lemurs to diurnal today: here are some photos of Indri, which are critically endangered. Indri only have a fluffy stump of a tail but have endearing faces. Their loud territorial ‘singing’ carries 2km, so they are relatively easy to track in the forests although hacking through undergrowth and up steep hills can be challenging. Indris are monogamous and live in family groups.