Lately I have noticed that upon spawn, there will be a large amount of a certain passive mob that will persist unless you exit the biome. For instance, I created a world for 1.9 pre5 and I spawned in a swamp biome. There were sheep EVERYWHERE. I found 1 pig. 1. In a 50 block radius I found 1 pig and 24 sheep. It's quite frustrating for me because in the first world I made for 1.0.0 there are chickens everywhere but I can't find 3 sheep for a bed and I'm now 15 Minecraft days in.
Has anyone else had this happening to them as well?