Male birds seem to 'judge' females by the color of their eggs!

 I was astonished to find out that many species of male songbirds actually base their mate choice on the color of the eggs she produces!  It turns out that there are some pretty sound physiological reasons behind the choices males make, despite the fact that on the surface it seems rather shallow.  Who knew that songbirds have such sophisticated means by which to assess the health and fitness of potential partners?