Mulitple chickens!
One hen could lay eggs quickly, one could be small (1x2) and only provide one meat but reproduce fast, one could be large (3x3) and reproduce slow but give three-four meat. One could eat loads of food but poop out really fertile poop usable as mulch or dirt or whatever.
One rooster could eat next to nothing but be lazy and barely ever fertilize eggs, one could do the opposite. One could be strong and venture outside the coop and catch rats and bugs and bring them back.
Sickness!
Chickens can get sick and die unexpectedly. Or suddenly get cannibalistic urges and attack, kill and eat others.
Adventure!
Chickens will go outside the coop and just wander around during the day and hide away at night. Momma hens will take their young out with them.
More chicken related stuff will be awesome!