Let's begin this post with two quotes. The first is one of my favourites, from Darwin's The Descent of Man:
It is a more significant fact that a female zebra would not admit the addresses of a male ass until he was painted so as to resemble a zebra, and then, as John Hunter remarks, "she received him very readily." In this curious fact, we have instinct excited by mere colour, which had so strong an effect as to get the better of everything else. But the male did not require this, the female being an animal somewhat similar to himself, was sufficient to rouse him.
The second is from William Blake's The Marriage of Heaven and Hell:
A fool sees not the same tree that a wise man sees.
So today I was asked about bird language. Birds tweet right? Isn't that language? Well, let's take a songbird like the blackbird. It sits on fence or on top of a hedge and sings its little heart out. Surely this has to mean something? No. It doesn't. What you have to do is move away from the aesthetic quality of the bird song (as perceived by humans) and realise why evolution has resulted in bird song (see the tree the wise man sees). Think about a peacock. Not a songbird. The male has a huge tail. Why? Well peacocks evolved in dense jungle, stalked by one of the largest predators on the planet, the tiger. Does it seem sensible for a male peacock to carry a huge tail in the presence of such a foe, when the terrain is so tough anyway? Does the peacock's tail help it navigate through the jungle? Far from it. Does it help it camouflage into the foliage? Again, far from it. So why does the peacock have such a large tail? Two words: sexual selection. Females choose the males with the largest tails to mate with. The next obvious question is, why? Let's look at it this way: A male with a large colourful tail is obviously tough. He has survived in a difficult environment, stalked by the most deadly of predators. The large tail is well maintained, colourful and bright. It indicates obvious genetic fitness and more generally, good physical health. A small, stunted male, with a dull tail, and teeming with parasites is not the kind of male that is going to produce successful offspring. Female choosiness (or selection) ensures that the healthiest males get access to females and therefore produce healthy offspring.
Okay Louie. but what about the blackbird. From his vantage on high, the blackbird sings his tune. He is not particularly large or colourful, but boy, can his song be heard by all around. Including by the predators. So as with the peacock, we can instantly deduce that blackbirds are a species where sexual selection is important. Females are selecting the healthiest males based on their display. But what about the song itself? Well like the tail of the peacock, the song of the blackbird is also being analysed by the female blackbird's brain. Whilst it is aesthetically pleasing to us, the female blackbird is analysing the song, from which it can determine the underlying health of the individual. Whether it is stunted and runtish, or loaded with parasites. Choosing the healthiest males again ensures that the next generation are the best they can be. Understand that this is not a conscious decision on the part of these animals: females choose the healthiest (or fittest) males to mate with, these in turn produce fit offspring, who are either a) discerning females or b) healthy males. Certainly nothing to do with language. And perhaps it is clear why the male zebra will mount any animal even vaguely similar to a female zebra, whereas the female is far more discerning?
Of course, this discussion is shallow. We could have covered the fact that the female contribution in reproduction is usually far greater than the males (think even the ovum is much larger than sperm) and thus it behoves (should that be behooves—remember the zebras?) her to be far more selective in choosing a mate than a male needs to be. It is also true that female selection like this removes somewhat the need for sexual aggression between males. Unless it is a fight to the death that gets access to the female, males have another chance next time round to impress the females. It's a strategy. (Note that blackbirds do engage in fighting between males, and that their singing may contain an element of aggression and display, the vocal equivalent of stags rutting. That doesn't undermine what has been said, just that evolution is both a simple and complex process.) Also, given the topic that stimulated the discussion was language in birds, we might have discussed the supposed evidence for simple language use in some of the so-called smart birds (like crows and parrots). A topic for another time maybe.Go Top