Leaf-Eating Monkeys: Red and Olive Colobuses

Zanzibar red colobus

The strict food requirements of red colobus monkeys make them one of the most endangered groups of African primates but they are still found across a surprisingly wide swathe of the continent. While we used to recognise only three or four species (albeit with many subspecies), it has become clear over the last thirty years or so that there are many more, around half of which are now restricted to very small areas. In most cases, this is because of the obvious reason that their old habitat has been destroyed and that they used to range further afield. Some, however, have never strayed far from home.

The easternmost species of red colobus falls into this latter category. Named the Zanzibar red colobus (Piliocolobus kirkii) this has historically restricted to the eponymous island. Since 1964, this has been the "zan" part of Tanzania, and lies just over 20 miles off the east coast of the mainland with an area of a little under 1,500 km² (565 square miles). With a human population of around 1,500,000 it is, as one might expect, substantially given over to agriculture and other development. As a result, while they once ranged across the island, they are now primarily found in the less settled eastern half of the island, where there are some inland national parks. In the 1970s, a small population was re-introduced to a patch of land on the west coast north of the main urban areas and others were translocated to Pemba Island to the north, where the species has never existed naturally. While one of the latter groups did survive and breed, their descendants are likely quite inbred and it has been argued that we'd be better off supporting the main population in their original home.

Leaf-Eating Monkeys: Red Colobuses of Central Africa

Ashy red colobus

The problem with being a primate subsisting primarily on leaves is that, on their own, they aren't very nutritious. Humans on a vegan diet can hardly be expected to live on lettuce alone; they need grains, pulses, nuts and so on, and we have the advantage of cooking making much of our food easier to eat and digest. Colobus monkeys have complex digestive systems that allow them to extract more nutrition from leaves than a primate would otherwise be able to, so they have the edge over us in that respect, but they still require plenty of fresh leaves and this leads to the more exclusively folivorous ones having specific habitat requirements that leave them vulnerable to any degradation or loss of their environment.

The end result of this is that many colobine monkeys are endangered. In Africa, the most endangered group, and probably the most threatened group of primates of any kind on the continent are the red colobuses.

Leaf-eating Monkeys: Black-and-White Colobuses

King colobus

The Old World leaf-monkeys are formally known as "colobine" monkeys, with the name of their subfamily coming from what British zoologist Thomas Jerdon considered to be the most typical member of their subfamily when he first named it in 1867. These, of course, are the colobus monkeys, of which there are a great number of species. Jerdon, however, was thinking in particular of what we would now call the black-and-white colobus monkeys, so it's these against which, taxonomically speaking, all other leaf monkeys are compared.

The first colobus monkey of any kind to be scientifically described was the animal now known as the king colobus (Colobus polykomos). This was in 1780, with Eberhard von Zimmerman basing his description on a specimen collected from an island off Sierra Leone. His original name meant something like "many-singing monkey", and it was only in 1811 that the word "colobus" was coined. This comes from the Greek word for "maimed" and refers to the fact that colobus monkeys have no visible thumbs, just a small lump on the side of the palm, making it look as if they have been cut off.