A while ago I bought one of those drinking birds to have around my desk at work. When I was in high school I bought one when given the opportunity during one of my science classes. Tragically that one met with an accident that ended in broken glass and chemicals. My current bird is still going strong (except the cloth around his head is very loose and fragile and will rip easily when it’s moist).
Yesterday Anna was asking me why I didn’t have any water for my bird ever since I took him home. So I got the cup I had been using at work and went for the filtered water. In my mind I was getting the filtered water because I knew the water could get a little gross since I don’t change it often, so hopefully filtered wouldn’t get gross as fast as tap water. In retrospect it does look like I’m concerned about the quality of water my drinking bird gets 
I’ve read wikipedia and saw http://www.youtube.com/watch?v=KUvHzFm29cg – but there’s one step I don’t get: step 5 in the wiki explanation. I get there is a pressure difference, but I find it hard to beleive that this pressure is easier to equalize by pushing up some liquid (high pressureon the liquid surface of the bottom bulb, while there is lower pressure on the liquid surface on the inner tube) than by the flow of gas trough the outer tube – unless that contains some sort of valve, which I don’t see in the explanations. Any physicists reading who can explain it to me?
I think it’s simpler than you’re making it sound. There’s different air pressure in the top and bottom, but when the bird tips, the end of the tube at the bottom is briefly exposed (whereas before it was submerged in the fluid) and then the air rushes through the tube, and once the bubble reaches the head it equalizes.
Yeah, I get that. But what I don’t get is why the pressure between top and bottom is equalized by pushing liquid up (trough the inner tube) instead of just having the gas flow up (trough the outer tube)
Ah, after reviewing the video I get it. The wording on wikipedia made me think that there was an inner and outer tube while in reality there’s only one tube. Now it makes perfect sense all!