I live in southern Michigan, USA. I've had a nesting box in my small suburban backyard for at least 15 years and have black-capped chickadees nesting every year. Something curious is happening this year. I set the nest box out on 31 March and chickadees moved in within two days. Now, a couple weeks later, chickadees are removing nesting material from the box. I don't see nesting material going in, just coming out. I wonder if more than one pair is competing for the box. I don't see chickadees fighting.