I don’t think there is a physics model for flight, but if you have a good grasp of maths or a willingness to learn, NASA has a great resource for basic aerodynamics.
http://www.grc.nasa.gov/WWW/k-12/airplane/short.html
It’s often necessary to simplify when you can to avoid doing a lot of calculations every frame or to collate a large table for values like the lift coefficient used to calculate overall lift. LiftEq
Helpful aproximations:
- Thin Airfoil Theory: Airfoil - Wikipedia
- Lifting Line Theory: Lifting-line theory - Wikipedia
- Drag coeficient: 0.4 for the drag coefficient of birds is probably close enough for small birds. per this paper
I know this probably isn’t the sort of answer you were looking for, I’m sorry to throw you to the wolves, but sometimes you might just have to buckle down and hit the books to get things done. If you’ve looked over the above and your just don’t know what to do, I can maybe try to direct you based on where you got stuck.