The saying "mad as a March hare" refers to the wild antics of male hares as they compete with other males in the spring. Their mating behavior with females often looks like a crazy dance.
The saying "they multiply like rabbits" probably refers to the ability of hares and rabbits to conceive a second litter while still pregnant with the first. It's not surprising that rabbits became fertility symbols. Rabbits, however, do not lay eggs, in case you wondered.
The idea of the egg-laying bunny came to America in the 18th century with German immigrants in the Pennsylvania Dutch region. They said that on Easter morning, good children found bunny eggs in their hats.
In Australia, there is a long-running campaign to replace the Easter bunny with the Easter bilby. The bilby, an endangered species, is a little smaller than a rabbit. It has a long nose and ears almost as big. A portion of the profits from selling chocolate bilbies goes to protection and research.