The Crested Macaques of Pulau Bacan: sightings, video and questions

Crested Macaque, Macaca nigra
Labuha, Bacan, 28 November 2022

We were very pleased to see the monkeys on the island of Bacan (pronounced as the old names for the island, Batchian and Bachian) in the Moluccas of Indonesia last November. After a bit of chasing round the town of Labuha in the vehicles, they were found in the first place we had looked—a regular site by the side of a road next to houses and wayside litter. I say monkeys because they have gone by so many different common names that it is difficult to keep up. In The Handbook of the Mammals of the World they are known as Crested Macaques, Macaca nigra, but that, with a combination of their place of origin (Celebes, now Sulawesi) and their jet-black fur has led, over the years to Celebes Crested Macaque, Black Crested Macaque, Celebes Black Macaque, Celebes Macaque, Crested Black Macaque, Sulawesi Black Macaque amongst even more when they were called ‘apes’ instead of ‘monkeys’. Black Ape and Celebes Black Ape were the common names used by zoos in UK for decades.

Below is a short video I took of the troop.

Bacan is east of Wallace’s Line and every description of the monkeys of Bacan describes them as ‘introduced’. Unlike on Sulawesi, west of the Line and to which they are native, the monkeys are thriving on Bacan. Research and conservation measures on Sulawesi the Macaca Nigra Project) as well as captive breeding populations in zoos throughout the world are aimed at preventing their decline for which hunting for human food is mainly held responsible.

Two questions struck me as we watched and photographed the monkeys.The first was: when were they introduced? Initially I drew a blank. Then I thought of looking in Wallace’s book, The Malay Archipelago.  He was on Bacan in 1858-59.

Batchian is remarkable as being the most eastern point on the globe inhabited by any of the Quadrumana. A large black baboon-monkey…is abundant in some parts of the forest. This animal has bare red callosities, and a rudimentary tail about an inch long—a mere fleshy tubercle, which may be very easily overlooked. It is the same species that is found all over the forests of Celebes, and as none of the other Mammalia of that island extend into Batchian I am inclined to suppose that this species has been accidentally introduced by the roaming Malays, who often carry about with them tame monkeys and other animals. This is rendered more probable by the fact that the animal is not found in Gilolo [Halmahera], which is only separated from Batchian by a very narrow strait. The introduction may have been very recent, as in a fertile and unoccupied island such an animal would multiply rapidly.

There has been the assumption which I will explore in a further article that the monkeys were present on Bacan in the late 1820s, the first known recorded date. Are there any earlier references to the presence of monkeys on Bacan in the Portuguese or Dutch literature from centuries earlier which have not yet seen the light of day?

So we still do not know the date or the manner of their presumed introduction to Bacan. And that leads me to my second series of questions: Has anybody looked at the genetic structure of the population on Bacan? Is there evidence of a past genetic bottleneck as a result of the introduction of very small numbers? If the population did start from very small numbers they have clearly avoided inbreeding depression on Bacan. The answer to these questions appears to be ‘no’. It is research waiting on a plate to be done and would extend the study already done on Sulawesi. Indeed, should, in the future, conservation efforts on the species come to rely on the population on Bacan, it is vital information on which to base reintroduction or genetic diversity programmes.

The part of Sulawesi in which these monkeys live is 300 km (180 miles) from Bacan. Was Wallace right in supposing ‘that this species has been accidentally introduced by the roaming Malays, who often carry about with them tame monkeys and other animals’? Or is there another explanation as to how the macaques crossed Wallace’s Line?