Cute game! I love the concept, and the controls were intuitive once I figured out what right clicking the chickens does.
A couple notes:
-The sound effects are nice but a little repetitive, especially in the menu screen where they are going off constantly. I second the chicken madness background music idea :)
-It would be nice if score upgrades glowed when you can purchase them, and also their symbols could be a bit more clear as to what they do (perhaps a clock with a down arrow for chicken speed and an up arrow next to the golden chicken for the increased golden chicken frequency).
-At a certain point (about 8 eggs in my games) purchasing more eggs does more harm than good by blocking the screen from chicken hunting, and I was able to subsist off of right clicking all the chickens until about 200 (nice work on the gradual difficulty increase!). Maybe if the chickens flew in front of the eggs there would be more incentive to purchase more eggs, although that might make it too easy.
Keep up the good work!