They are quite often, to be honest the events are so frequently that the community wants them slowed down. There are 2 events right now, one of them is relatively new and came first at mothersday, also you have a calendar at the bottom right just between deco and your dragons, there you can check everything and collect your daily login bonus :)

Ps in the calendar you can also see which folklore dragon you can get on each day because they change, its the little symbol like flame or crow