Red-handed howler

The red-handed howler (Alouatta belzebul) is a vulnerable species of howler monkey, a type of New World monkey. It is endemic to Brazil, found in the southeastern Amazon and disjunctly in the Atlantic Forest between Rio Grande do Norte and Sergipe.

Taxonomy

Considerable taxonomic confusion has surrounded this species. Until 2001, most authorities included the Amazon black howler as a subspecies (or simply a taxonomically insignificant variation) of the red-handed howler, though its distinction had already been pointed out much earlier. The red-handed howler remained variable in ecology, colour and pattern of the fur, shape of the cranium, and shape of the hyoid bone (of great importance in the voice of the howler monkeys; a likely isolating mechanism between the species), but a geographical pattern was not clear, resulting in it being treated as a monotypic species. In 2006, a major review of the Brazilian members of the genus Alouatta was able to match some of the variations to geography (though further study was recommended), resulting in the recognition of the Spix's red-handed howler and Maranhão red-handed howler as species separate from the red-handed howler. Even with these as separate species, the colour and pattern of the fur of the red-handed howler remains variable. Most adults are black with reddish-brown hands, feet and distal part of their tails, but some are entirely black (resembling the Amazon black howler), reddish (resembling the red howlers) or somewhere in between.

Physical Characteristics

The red‑handed howler has red hands and feet, while its fur is black or dark brown across the rest of the body. Adult males typically weigh between 7 and 9 kg (15 and 20 lb), measure around 90 cm (35 in) in head-body length, and exhibit significant sexual dimorphism in size and stature.