Eulemur collaris is a medium-sized lemur with a head-body length of 39–40 cm, a tail length of 50–55 cm, an overall length of 89–95 cm, and a body weight of 2.25–2.5 kg (Tattersall, 1982). This species is sexually dichromatic. In males, the dorsal coat is brownish-gray, the tail is darker, and there is also a dark stripe along the spine. The ventral coat is a paler gray. The muzzle, face and crown are dark gray to black. The creamy to rufous-brown cheeks and beard are thick and bushy, while the creamy to gray-colored eyebrow patches vary in their prominence. In females, the dorsal coat is browner or more rufous than that of the male. The ventral coat is a pale creamy-gray. The face and head are gray. The cheeks are rufous-brown, but less prominent than in the males. Both sexes have orange-red eyes. The red-collared brown lemur is similar in coloration to Eulemur cinereiceps. Male E. collaris can be distinguished from male E. cinereiceps by their beards, those of the former being cream-colored or rufous while those of the latter are white. Female E. collaris are virtually indistinguishable from female E. cinereiceps (S. E. Johnson, pers. comm.). Recent genetic analyses support full species status for both taxa (Djletati et al., 1997; Wyner et al., 1999b).
Very little information has been published regarding the natural history of this lemur. It is an inhabitant of moist tropical forest, and appears to be common where it occurs. Irwin et al. (2005) estimated a population density of 14 individuals/km2. It is believed to be largely frugivorous and cathemeral, meaning that it is active both day and night throughout the year. Social groups tend to be multi-male/multi-female. Female dominance has not been observed (Donati, 2002; Bollen et al., 2004).
The red-collared brown lemur is found in tropical moist lowland and montane forests in southeastern Madagascar, from Tolagnaro (= Fort-Dauphin) north to the Mananara River. The western limits of its range are the forests of the Kalambatritra region, including the Kalambatritra Special Reserve. The Mananara River serves as a boundary between the ranges of E. collaris and E. cinereiceps, except for an isolated population at Midongy du Sud National Park (Irwin et al., 2005) and another at Vohipaho, near Vangaindrano (S. E. Johnson, pers. comm.). There is also a small population in the Sainte-Luce Private Reserve.
The 2008 IUCN Red List assessment classified E. collaris as Vulnerable (VU). The principal threats are habitat loss due to slash-and-burn agriculture and charcoal production, hunting for food, and capture to supply local pet trades (Raharivololona and Ranaivosoa, 2000). It occurs in the national parks of Andohahela and Midongy du Sud, in the Kalambatritra Special Reserve, and in the Sainte-Luce Private Reserve (Nicoll and Langrand, 1989; Mittermeier et al., 1994; Wright and Porter, 2004; Irwin et al., 2005). It is also found in the Mandena Conservation Zone, privately maintained by QIT Madagascar Minerals (QMM) (a partnership between the Government of Madagascar and Rio Tinto, in the development of an ilmenite mine near Fort-Dauphin). Six to eight orphan E. collaris that had been purchased in the Forte-Dauphin market were introduced into the Berenty Private Reserve over some years up to 1985. Other red-collared brown lemurs were introduced to the Kaleta Private Reserve nearby, and they also spread into Berenty. They hybridized with E. rufifrons which had been introduced previously (Jolly, 2004; p.30; pers.comm.). As of 2009, there were 37 red-collared brown lemurs reported in zoological collections in Europe and North America (ISIS, 2009).
Eulemur collaris is most easily seen in the Mandena Conservation Zone, approximately 20 minutes east of Tolagnaro (= Fort-Dauphin), and in the Sainte-Luce Private Reserve, about three to four hours north of Tolagnaro along the coast. The Mandena Conservation Zone can be visited with the help of local tourist agencies or through contact with QIT Madagascar minerals in Tolagnaro. The Sainte-Luce Private Reserve is owned by M. Jean de Heaulme, the owner of Berenty, and arrangements to visit can be made through the Hotel le Dauphin in Tolagnaro. Another site is the rain forest portion (Parcel 1) of the Andohahela National Park, especially along the road to the Col de Manangotry. This area is a few hours drive by car from Tolagnaro and arrangements can also be made through all local tour operators.