Chickadees are small, plump birds that are found in North America and parts of Europe. They are part of the tit family, which includes tits and titmice. The term 'CHICKADEE' is derived from the sound they make, which is a two-note call that sounds like 'chick-a-dee-dee'. They are known for their intelligence and curiosity, and they are often seen at bird feeders. The four-letter solution to the crossword is TITS, and the seven-letter solution is TITMICE.