Why do some birds stand on one leg?

One of the more widely accepted theories is that some birds stand on one leg to conserve body heat and energy. :)

http://www.wisegeek.com/why-do-flamingos-stand-on-one-leg.htm 

Hi,
I must be honest.  Your question surprised me.  I had no idea.  I spent hours trying to find the answer.  Was not easy but I've got it: 
1.  The only exposed parts of their body are legs and   
     head.  To avoid massive heat loss they stand on 
     one leg.
2.  Standing on 1 leg enables them to tilt their head
     backwards into the fethers.  That's a 2nd way to
     conserve heat.
3.  Another theory: This position is less frightening
     to the prey (fish. frogs, etc). 
4.  And some think that in this possition the bird put
     a shade that provides some advantage in catching
     it's prey.
Best regards,

to save heat and energies 

While a theory like conservation of energy makes sense, I have the strange feeling that scientists will come up with other theories to explain this behavior.  (Though standing on one leg minimizes heat loss, it would also seem to put more stress on that leg.  Personally, I'd think that the disadvantage cancels out the advantage.)

Because they saw their mom and dad and all their friends do it!....but seriously the posture may be the only way it can sleep- saving energy body exposure and position its head in a semi concealed fashion. Most birds do it so it must be a comfort physiological posture.