Why is it that the only birds that can see the colour blue are owls?

Question: Why is it that the only birds that can see the colour blue are owls?
- Keywords:
  bird,
  blue,
  colour,
  colour blind,
  owl,
  sense,
  sight,
  vision
Asked by lizzierd to Jo, Kevin, Valeria on 21 Jun 2012.
- Kevin Mahon answered on 21 Jun 2012:
  
  Owls are hunters and nocturnal over the course of evolution, the eyes have become larger and more sophisticated in order to see and catch prey running at high speeds at night time – consequence of this is that they can see blue, as their advacned eyes can see a much broader spectrum of colours.
  
  Other birds, that mostle hunt during the day don’t need such sophisticated eyesight – therefore it posed no advantage for them to have it and therefore it didn’t evolve.
- Joanna Cruden answered on 21 Jun 2012:
  
  As Kevin says they do seem to be the only birds that see blue and I thought you may be interested in one of the tests used to find out what colour an animal can see:
  
  The cognitive vision test. You teach animals to press one button if the colors are alike and another if the colors are different. Then you present them with colors that are different if you have color vision but alike if you see in black and white (the same saturation of shade, but different spectrums). Then you see what sort of decision they make

Question: Why is it that the only birds that can see the colour blue are owls?