Harsh cries ring through the jungles of central India in summer: the call of the peacock. I normally ignore the Indian peafowl (Pavo cristatus). They are commoner than crows and pigeons when you enter the open jungles of this region. But as the monsoon’s breeding season approaches I keep a watch for the mating display of the male. If you are lucky enough, you can get a photo that is worth the halt. Sometimes you see a lek: a group of males all displaying together, for the benefit of a seemingly uninterested female. This is perhaps its core behaviour. The female selects a mate based on the size and colour of the train. Growing a large train takes energy, in terms of health and food, and the ability to escape predators. There’s no faking it. At the same time, the female’s preferences selects the biggest trains, and therefore the offspring are likelier to have big trains. Repeated for generations this pushes the species into the direction of males with more spectacular trains. Since the genus could be recognized in 18 or 19 million years old fossils, most species in the genus have evolved towards bigger trains.
Unfortunately the only peacock I’ve seen is Pavo cristatus, the Indian peafowl. Native to Bangladesh, India, Nepal, Pakistan, and Sri Lanka, breeding populations have been introduced in Singapore, Taipei, the UK, and the USA, largely in Florida. I’ve yet to see its larger cousin, the Green peafowl (Pavo muticus). It is disappearing fast in Myanmar, but I suppose on a trip to Thailand, Vietnam, or Cambodia, or even in the extreme east of India, I could plan to visit its habitats. It is a little astounding that viable hybridization between P. cristatus and P. muticus can be established. It seems that the reason is that in birds cellular evolution is slow, and two species like this, which have separated only three million years ago have not changed sufficiently for their crosses to be unviable. I wonder whether anyone has tried crossing the Congo peafowl (Afropavo congensis) with either of the Pavo.
An interesting thing about the feathers is that they never fade. That is a clue that the colours are not due to pigments; pigments would oxidize over the years and change. The iridescent colours are due to, well, iridescent diffraction of light. Microstructures in the feathers produce the specific wavelengths that are seen, and a little change in the shape and size is enough to change colour. I’m surprised that a comparative study of the feathers of the peafowls has not been done. It seems that feathers don’t fossilize well, otherwise it would have been possible to examine the feathers of the extinct European peafowl (Pavo bravardi in the south and Pavo aesculapi in the north) and tell their colours. It is strsnge that so little is known about birds as spectacular as these.