Our chapter has adopted the bunny as its mascot as well. I know there is a chapter in Florida (not sure which one) that uses the Zebra (how cute!).
I have always loved rabbits anyhow, so it was just an added bonus for me that my chapter has this mascot. We have also now adopted FAMILY mascots- different animals for each "family" of bigs/littles.
The bunny doesn't have any particular symbolism for us other than it has always been our chapter's mascot. I just think bunnies are cute and very easy to find for giving presents to Littles (it's especially great when they're on sale after Easter). I've also been able to find many items in the Spring/Summertime that have both bunnies & strawberries on them, or bunnies with crowns on their heads.
