Monday, 25 June 2012

Turacos Part 1

Great Blue Turaco
Living in woodland areas all over Africa from primary rainforest to wooded savannah are at least 23 species of more or lesss chicken-sized, usually brightly coloured, birds belonging to the family Musophagidae. Commonly called Turacos, some species are called Go-Away-Birds after their call, or Plantain Eaters. At Bristol we currently have three species, and the next few posts will cover each of them.

White-crested Turaco
There are six genera in the Musophagidae. The brightly coloured forms are the various species of green Turaco in the genus Tauraco, the purple Turacos in Musophaga, plus two monotypic genera, the Ruwenzori Turaco in Ruwensorornis and the largest turaco, the Great Blue Turaco in Corythaola. The other two genera are birds with usually grey and white plumage the Go-Away-Birds in Corythaixoides and the Plantain-Eaters in Crinifer.

Grey Go-away Bird
The colours of turacos are practically unique amongst birds. The green colour is a true pigment called turacoverdin, and red colours from a related pigment called turacin. In other birds green colours are result of a mixture of yellow pigments in the feather combined with a particular microstructure in the feather which gives a blue appearance. In domesticated birds, mutations often arise which remove either the yellow, the blue, or both, and the remaining pigments (if any) then show through. This is how the wild-type green budgerigar gave rise to blue, yellow, and white versions in captivity. In turacos this does not occur, but the different pigments are actually soluble in a weak alkali solution. Placing a turaco feather in such a solution will extract the colour. Why they evolved this unique behaviour is not at all clear, nor at what point it appeared. Whether the grey genera represent the original stock or have secondarily lost the pigment is not clear at present.

Eastern Plantain-Eater
The diet of turacos is heavily biased towards various fruits, but there is some variation between the species. Great Blue Turacos and Go-Away-Birds also eat large amounts of foliage, and many species supplement the diet with snails, insect larvae, and other invertebrates. In common with many frugivorous birds, animal protein is especially important during the breeding season.

Turacos nest in an open, cup-shaped nest and lay 2-3 eggs. The chick will leave the nest at only 2 weeks, well before it can fly, and clambers along the branches. In this it takes after its parents – turacos even as adults are poor fliers and mostly run along branches, taking only short glides from tree to tree. As such they make an interesting potential model for flight in early birds, although they themselves are fairly advanced birds and are possibly related to the rather turaco-like Hoatzin of South America. If there is a connection it goes back a long way – modern turacos appear quite incapable of spreading across even small water barriers, let alone an ocean. Some fossil forms appear to have existed in Europe and they may have spread via island-hopping from there to North America and then south during periods when the North Atlantic was far narrower and temperatures in the northern hemisphere were higher. Although turacos look tropical, many species are surprisingly cold tolerant – escaped specimens of White-Cheeked Turaco have survived several years in the wild in the UK, despite snow and ice. There is one that lives near Bristol the one of my fellow volunteers has seen on several occasions – apparently it visits bird tables for peanuts!

White-cheeked Turaco - have you seen this in the UK?
Next week, the first of Bristol’s species, Fischers’ Turaco

(images from wikipedia)

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