The notion of birds calculating the fractal dimension of a prospective mate's feathers seems about as farfetched as baseball fielders calculating the exact mathematical damped parabolic path of the ball to work out where to put their hand. It also indicates that if true, birds are much nerdier than my physicist friends and should in theory have less chance of getting a date. As such, this theory is debunked by birds not being extinct through lack of mating! I do buy the notion that birds could see the effect without doing the maths though.