Do the critters (rabbits, birds, penguins, etc..) do anything?

Do they play a role later on in the game (hard mode, having a certain NPC), or are they just a random addition to the game?

2 Answers

They most certainly do nothing. They are, as you said a random addition to the game.You don't get anything from them when you kill them, and they have very little health. Buuuut that said you can capture them with a butterfly net then eat them... yum.

3

The bunny you can make into ammo for the bunny cannon. aside from that, bugs can be used for fishing (Personally, I use critters for target practice). That's all I use them for. There is,however, a slim drop chance for the boss summoning items (mechanical eye, mechanical worm, and mechanical skull). They are useless in pre-hardcore however.