Why are some birds so bonny?

[Tursiops2]

It's an interesting question .

My own observation is that white (or yellow) wing bars/tail feathers/rumps etc., which are particularly conspicuous in flight, seem to occur mainly in species which habitually form flocks, so I've always assumed that they evolved as way for birds to maintain visual contact in poor light. There are obvious exceptions to this: Wheatears, although sociable, don't seem to form dense flocks, but they do have conspicuous white rumps; and Starlings, which do form tight cohesive flocks, dont have any conspicuous flight markings, so there are probably additional factors involved.

On the question of sexual dimorphism (where males have elaborate plumage but females are drab and inconspicuous, e.g. the Peacock's "fan"), one theory is that this evolved as a way of demonstrating physical fitness to potential mates, i.e. "if I can survive with this lot on my back, I must have good genes".

T2