No, despite appearances to the contrary I have not abandoned my blog. I hope one or two of you may still be visiting.
Some time ago you'll recall I was pleased and surprised to be visited by a white budgerigar. It seems that the larger exotic birds are not to be outdone however, as around six-thirty one morning in recent July, I was delighted to encounter a couple of Peafowl pecking around on my lawn. I hastily grabbed my camera and achieved the not-very-good photo (left) before they fled over the wall. I assume my birds came from a local farm or some country estate, but I do not know from which.A few minutes internet searching informed me that my birds are Indian Peafowl (Pavo cristatus), as opposed to the endangered Green Peafowl (Pavo muticas) from Java and Burma. Males of the latter species can be identified by a tall, spiky crest on their heads.
Much the most famous feature of peafowl is of course the peacock's fantastic fan tail (sadly mine didn't display). Ever since Darwin, naturalists have been fascinated to understand what possible evolutionary purpose it can serve to sport such an unwieldy appendage; The benefit of carrying around a large iridesceant sign, seemingly pefect for announcing to predators "Here I am! Eat me!", isn't obvious!
My quest to understand a little more led me to an excellent review paper by one R. Gadakar (here). In brief, my understanding is as follows: As a Peahen, one approach to selecting a mate is to choose those males who most strongly advertise their health and vitality with a large fan. So far so good, but the question this poses is whether the extravagant fan we see today has arisen because at some point in history females selected to breed with males with a slightly longer tail, which led to male-offspring with slightly longer tails, from which later females again selected the longest...i.e. whether today's fan is a result of 'run-away selection' (in which case the fan is beautiful but it is not, per se, an honest indicator of the male's health). Or whether an alternative hypothesis holds i.e. the so-called Zahavi's handicap idea, which states that any male able to carry around such a huge encumbrance and yet still survive (evade predators etc.) must somehow be truly fit and strong i.e. the tail is not only beautiful but also honest indicator of the fitness of the male.
I have failed to think up a simple way to restate this (indeed, as the paper above says, the trend in biology these days is to get away from the vagary of mere words and express things in terms of mathematical models where possible), but a (very incomplete) analogy might be following: some female humans prefer their men well muscled, as a sign of their vitality. For the humble male there are then two routes to getting-the-girl: One, a regime of healthy food and physical exercise. Two, steroids and plastic surgery! The latter may achieve the visible appearance of the 'body beautiful', but it could hardly be called an honest statement of the chap's health and fitness. By contrast, in seeking to achieve the rippling musculature beloved of the ladies, the former approach requires males to accept the 'handicap' of limited diet and punishing gym sessions, but in the long run this 'handcap' is actually likely to positively benefit both their own and their offspring's health.
The existence of this, the (Zahavi's) handicap hypothesis out there in nature however was controversial amongst evolutionary biologists when it was first suggested, and therefore it has been important to find ways to test it. Which brings us back to peacocks: Glass-jawed weaklings beneath steroid-inflated shells, or supermen in both looks and deeds?
Some of the definitive studies of peafowl have been performed on a feral population at Whipsnade Zoo here in the UK Firstly it is known that peahens select those peacocks with the most symmetric tail fans. High symmetry is strongly correlated with a large number of eye spots. And what have the studies at Whipsnade concluded about those males with the highest eye spot count? That they i) have better reserves of body fat ii) have higher survival rates (against loss to foxes etc.) and iii) father healthier, fatter chicks.
In short, no preening primadonna he, the male peacock really is both both beautiful and honest!
