At this time of the year, gray squirrels are breeding. After they breed, the females start looking for a place to build their nest and have their young. They prefer hollow trees, but will get into attics, or build a nest (made out of twigs and leaves) in the crotch of a tree branch. One annoying habit they have, however, is that they will check out chimney tops as possible nesting sites (thinking they are hollow trees) and if they fall down the chimney, they are trapped. The flue liner inside the chimney is too smooth for their claws to hang on to, so they can't climb back out. If the damper on the fireplace is closed, they are trapped on the smoke shelf above the damper. If the damper is open, Oh, Oh, they are in your fireplace. Hope you have glass doors on the fireplace, if you don't, they could be in your house. They can also fall down chimneys into wood stoves, if they are connected to a chimney. They also sometimes fall down chimneys right into furnace pipes. They normally don't survive this. There are two basic ways of removing them. The first is dropping a very heavy (at least 1" in diameter) rope down the chimney from the top, thereby giving them something to climb out on. If you attempt to "do this at home", use extreme caution. Some newer houses are built with roofs that make this almost impossible without special equipment to get you up there. The second way is to go into the fireplace, grab the squirrel, and carry it outside and let it go. Not recommended for amateurs! This whole problem can be prevented by getting your chimney(s) capped. That will keep out raccoons, also.