I know it's just an early demo but after playing it for a few hours I thought I give some feedback.
Overall the gameplay is really great, there are some thing that i think possibly could make it better. As it is now you can only control the birds flight upwards. And since you attack from above it makes it sometimes hard to make the attack. What if you could descend more rapidly by pressing down.
You pick up stones just by passing them which makes it a bit annoying when you don't want a stone. You need to drop it and then move quickly away so you don't accidently pick it up again. I think it would be better if you pick up a stone by pressing a button.
Flying with a stone is very hard. I would suggest making the stones just a bit lighter.
Some random things:
On the first level you can just pass the ice-column. So why do you want to break it?
You also get a point just by passing the seesaw, shouldn't you get a point by breaking the ice-column?
Suggested features:
Bombs, we gotta have bombs, that when you pick them up a timer starts and if you don't drop it at the right time you blow up (with a nice animated explosion)
Bonus stages were you can't die but collect extra point by showing of your amazing flying skills.
Well that was some suggestions, great game so far and I look forward to seing a new tech demo soon.