Odd colour morphs in leaf monkeys

Madura De Silva and colleagues and I recently, independently, published papers on odd colour morphs in leaf monkeys. They documented a white phase of the Sri Lankan langur Semnopithecus vetulus (they are usually grey) and I documented a red phase of silvered lutung (or leaf monkey), Trachypithecus cristatus. (see references at end of post).

This is most interesting and it doesn’t happen very often. Unlike other taxa such as birds, which often have different color morphs, primates rarely do. I suppose this is because in mammals, when there is a mutation that causes a colour morph, either natural selection or sexual selection quickly eliminates it. One can imagine, for example, that a white morph of S. vetulus might be more visible to eagles, and so predation pressures might eliminate them. But De Silva's photos and mine also show that some white S. vetulus and red T. cristatus have babies, and so negative sexual selection must not be much of a factor. It is even possible that sexual selection could be a positive force, meaning that white potential mates are attractive because of their differences. As we say, “Variety is the spice of life!”.

In the case of the red T. cristatus, since they were documented some 70 years ago and still persist, indeed seem to have spread far upriver, one can speculate that there must be something about their environment that either doesn’t discriminate against red ones (for example, lack of avian predators), or actually encourages them. The only big eagle we saw was the Crested Serpent-eagle, and I presume that this is a snake/lizard specialist. Large snakes and wild cats of all sizes up to Clouded Leopard are present in Kinabatangan River habitat of T. cristatus, but I don’t know anything about their colour vision. It might be that red is just as invisible to these predators as black, maybe even more so. The black ones were certainly more visible to me, everywhere I have seen them (several places in Borneo and also in Peninsular Malaysia). Also, since there is a red species of leaf monkey, Presbytis rubicunda, that lives in the same area, there is obviously no environmental factor that would negatively affect T. cristatus.
About S. vetulus: it would be interesting to know how long they have persisted. Since De Silva et al mentioned a pale specimen from 1923, it seems possible that some variation was present 90 years ago, and may have increased in proportion and also in whiteness since then. If predation is a factor in coat color, would it be reasonable to speculate that since 1923, predation pressure might have slackened? Perhaps some of the langur predators have declined in the region where the white morphs persist?

References

SILVA, M. A. D., N. C. HAPUARACHCHI, AND P. A. R. KRISHANTHA. 2011. A new colour morph of Southern purple faced leaf langur (Semnopithecus vetulus vetulus) from the rain forests of southwestern Sri Lanka. Wildlife Conservation Society – Galle: 16.

HARDING, L. E. 2011. Red morph of silvered lutung (Trachypithecus cristatus) rediscovered in Borneo, Malaysia, Taprobanica 3:47-48.

Wildlife Watching in Vietnam

Stepping out from my room in the guest house at the main ranger station in Cuc Phuong National Park, I paused in the darkness on the tiled veranda. This was my first morning ever in Southeast Asia and I wanted to savour it. A sharp, peaked hill loomed against the stars behind the guest house, brightened on the east side by the looming dawn. In front of the guest house, the terrain dropped away from the hills toward the lowlands. The tropical forest was coming alive with calls of birds that I didn’t know yet, but would soon see: babblers, laughingthrushes, and many others. In a few moments I would meet my guide for a few hours of birdwatching before breakfast. Suddenly there occurred one of the most profound moments of my life. Loud calls, whoops, and yells erupted from the black forest below the station, and were immediately answered by similar cries from the hills above. The calls from below were from several species of gibbons, long-armed swinging apes, and langurs, a type of monkey, that were housed in the Endangered Primate Rescue Center adjacent to the ranger station. The calls from the surrounding hills were from wild gibbons. Like us, gibbons are monagamous and probably mate for life (although this isn't known for certain for all species) and in the morning each pair sings a duet with complementary male and female parts. This is one of the few places in the world where these species can be seen in the wild. All are on the brink of extinction. The ones I heard behind the guest house were white-cheeked gibbons Nomascus leucogenys. Besides the gibbons, 2 species of loris: Nycticebus pygmaeus and N. bengalensis; and 3 species of macaque: (Macaca mulatta, M. assamensis and M. arctoides) live there.
Vietnam has a great variety of monkeys—24 species—and many are rare. Five are endemic to Vietnam (they occur nowhere else) and are among the most endangered primates on Earth. I arranged my trip through the tourism department of Cuc Phuong National Park (www.cucphuongtourism.com). Established in 1960, it is the oldest and largest nature reserve in Vietnam and located only 120 km from Hanoi, the capital. It is also home to the Endangered Primate Rescue Center (www.primatecenter.org) that houses primates confiscated from poachers, conducts research into their biology and life history, and breeds them for release into the wild.
The guide met me with a car and driver at the airport and took me straightaway to Van Long Nature Reserve, stopping for lunch at Ninh Binh, a village on the edge of the vast, fertile, and populous plain of the Red River (Sông Hðng). Soon we stood on a dike overlooking a long, narrow marsh that disappeared in the distance between high, limestone cliffs. A tiny woman ushered us into an equally tiny boat, its gunnels barely inches above the water, and began to row across the marsh. In a moment we turned up a winding creek between limestone cliffs. The sharp-eyed guide pointed to a group of Delacour’s langurs scampering along a cliff, their white rumps, thighs, and cheek whiskers contrasting with otherwise black bodies. On our return at sunset, a brisk headwind slowed our progress and I could see that the boatwoman was struggling. I asked if I might be allowed to row. Surprised, she looked at the guide and said something questioningly that included the word, “American.” The guide shook his head no, and said something that included “Canadian.” She handed me the oars and, carefully so as not to upset the craft, we changed places and I began rowing strongly. She grinned at the guide and they exchanged a few more words. Later he translated them as roughly, “Oh, well, if he is Canadian, of course he can row.”
I saw an amazing variety of birds, most unrelated to anything I had seen before and boasting astonishing colourful plumage: green magpies, blue-winged leafbirds, flamebacks, green-billed malkohas, three kinds of pittas, canary-flycatchers, sultan tits, and many kinds of babblers, fulvettas, yuhinias, flowerpeckers, sunbirds, and many others. The park list is 307 birds long; in three days I added 75 to my life list. After birding and wildlife-watching there and around the main ranger station, the guide drove me to Bong Station, deep in the interior of Cuc Phuong National Park for another couple of nights. That evening, while walking down a dark road from my one-room chalet to the dining hall, I saw a light glinting beside the road, and then another. Could it be a wild cat? a civet? a weasel? But then more lights appeared, not in pairs, and they began randomly moving around, up in the air and everywhere—they were fireflies! Actually, beetles. It was like walking among the dancing stars of Heaven.
I thought I had hired a bird guide, but in the morning, when we paused atop a trail summit, I asked him about mammals. Immediately, he began reeling off a list of mammals known to inhabit Cuc Phuong National Park: serows, a goat-like ungulate, sun bears (Helarctos malayanus), Asian black bears (Ursus thibetanus), two species of deer, red muntjak (Muntiacus muntjac), leaf deer (Tragulus javanicus), wild pigs (Sus scrofa), dhole (Cuon alpinus), racoon dog (Nyctereutes procyonoides), tiger (Panthera tigris), leopard (Panthera pardus), clouded leopard (Neofelis nebulosa), Asian golden cat (Catopuma temminckii), leopard cat (Prionailurus bengalensis), fishing cat (Prionalurus viverrinus ), Owston’s civet (Chrotogale owstoni) and variety of smaller predators including other civets, genets, palm civets, mongooses, and the binturong (Arctictis binturong). In all, 89 species of mammals inhabit the park and more are still being discovered (see http://www.vqgcucphuong.com.vn/English/ for more information). While we talked, a black giant squirrel (Ratufa bicolor), jet black with white cheeks and an orange underside, leapt among the branches nearby.
Unfortunately, many of the species we saw are endangered, some critically so. The whole world population of Delacour’s langurs, for example, may not number more than 200 individuals. Poaching is rife and a new biodiversity protection law offers scant protection. Primates, especially, are highly valuable as meat, alleged health products, and pets; although many are consumed locally, there is a vigorous trade north into China. See http://www.traffic.org/ for more information on illegal traffic in wildlife in Vietnam.
References:
A Guide to the Mammals of Southeast Asia, 2008. Charles M. Francis.
Birds of Southeast Asia, 2005. Craig Robson.
Mittermeier, Russell A., Jonah Ratsimbazafy, et al. (2007). "Primates in peril: the world’s 25 most endangered primates, 2006 – 2008." Primate Conservation 22: 1–40.
Nadler, Tilo, Vu Ngoc Thanh, et al. (2007). "Conservation status of Vietnamese primates." Vietnamese Journal of Primatology 1(1): 7-26.