Schalow's Turaco (Tauraco schalowi)
Photo: John Puddephatt (Wikimedia Commons)
Victoria Falls is awe inspiring: a narrow gorge of sheer cliffs, curtains of foaming white water, and a thunderous din that sends your senses into overload. But I'll be honest, I've never been a waterfall type of guy. So, after none to long a time admiring one of the world's largest spectacles, I was off to explore some of the smaller things that Zambia's Mosi-oa-Tunya National Park had to offer.
Below the falls I found a trail that ushered me down into the river canyon, away from the people, and away from the piles of trash that littered the pathways. The roar of the falls stayed with me as I descended sharply from the dry thorn forest at the canyon rim into a narrow oasis of succulent greenery. The rocks dripped with moisture. The palms grew lush and vigorous, and gracefully arched over the trail. African Golden Weavers (Ploceus xanthops) burst from the generous undergrowth, chased each other along a small vine-choked creek. A Spectacled Weaver (Ploceus ocularis), shinning like a lamp in the shady oasis, sipped water from a puddle.
Then there appeared another bird, a bigger, more ungainly one. A bird as green as the leaves among which it sat. It was one of the turacos and it's long white-edged crest meant it could only be Schalow's Turaco (Tauraco schalowi), perhaps the most elegant of all the Musophagidae. Schalow's Turaco can be a challenge to see, they are patchily distributed in pockets of dense riparian vegetation, like the sort I found below the falls. There's excitement in finding a good bird, and an interesting looking one at that: an oddly proportioned tiny red bill, red and white eye markings as though it got a little too ambitious with eyeliner, and a long and animated crest. But what most excited me about Schalow's Turaco was the simple fact that it was green.
Green birds aren't all that rare. In fact along the shore of the Zambezi River it's possible to see African Green Pigeon (Treron calvus) foraging in the treetops, green-backed Allen's Gallinule (Porphyrio alleni) and African Swamphen (Porphyrio madagascariensis) mucking around in riverside wetlands, and gregarious Green Wood-Hoopoes (Phoeniculus purpureus) nosily chattering as they explore the spiny acacias. There too are Dideric (Chrysococcyx caprius), Klaas's (Chrysococcyx klaas) and African Emerald (Chrysococcyx cupreus) Cuckoos, more often heard than seen, but they're all as green as green can be. The Narina Trogon (Apaloderma narina) is strikingly countershaded: iridescent green above, deep red below. There is a whole cast of greenish bee-eaters, in their ostentatious costumes, and foraging among the flowering riparian trees and shrubs is the Marico Sunbird (Cinnyris mariquensis) and its relatives. But there is a difference between the green that all of those birds sport and the green of the Schalow's Turaco. It's that difference that makes turacos unique among birds.
The greens worn by parrots, trogons and others, are usually produced through an interaction between carotinoid-based yellow pigments and the light-scattering effects of a feathers' microscopic structural characteristics. This is what we call structural colouration. Turaco green is different in that it is actually a green pigment called turacoverdin, which as the name suggests is found exclusively in turcos (though jacanas, Blood Pheasant [Ithaginis cruentus] and Crested Wood-Partridge [Rollulus rouloul] have a nearly identical pigment), and it's one of the only true green pigments found in birds. Pigments differ from structural colours in that pigments are completely independent of the way light interacts with a feather's microstructure. To illustrate just how different these forms of colour are try this:
Go next door and pluck a green feather from your neighbour's noisy Yellow-crowned Amazon (Amazona ochrocephala). You know what, the damn bird is awfully loud, take a handful of feathers; after all, you may want to repeat this little experiment at your next naturalists cocktail party. Got some feathers? Good. Now, grind one up with that useless mortar and pestle you keep squirreled away in your kitchen cupboard for some unfathomable reason. Put some muscle into it, pulverize it. Now look at it closely, under a microscope if you can, a hand lens will probably work too. What colour do you see? Green? No, I didn't think so; at least not if you ground sufficiently, destroying the structural components that actually make the feather appear green. Your feather powder, I'm guessing, probably looks grey or maybe a bit yellowish, but the green should effectively be gone. Now do the same thing with a turaco feather. What are you waiting for? Hop on a plane to Zambia, I know a spot... If you were to repeat this little exercise with a turaco feather, you'd be left with a green powder. Since turaco green is independent of feather structure, it will remain green even when pulverized. So, you might say that parrots, trogons and the other green birds of the Zambezi only appear to be green, but turacos actually are green.
Turacoverdin is high in copper. It may be that turacos actively seek out copper-rich fruits, buds and other foods. Alternatively, it could simply be that their diet may be naturally rich in copper and excess copper is sequestered out of the body and used to build green feathers. The function of green feathers is assumed to be for camouflage. Indeed most of the bright green turacos are forest dwellers, while most of the non-green turacos, such as the familiar and noisy Grey Go-Away-Bird (Corythaixoides concolor), live in more open habitats where bright green plumage may not be as advantageous.
Interestingly, turacoverdin isn't the only pigment that's exclusive to turacos, another chemically similar pigment, turacin is also a Musophagidae autapomorphy. Turacin is responsible for the red bill and facial markings of Schalow's Turaco and other species. Why turacos should have two exclusive (or nearly exclusive) pigments while most other bird families do not, remains a mystery.
