Can anyone identify this bird?

by Christine
(Kitchener, Ontario, Canada)

These birds returned numerous times to the top of a dead tree on an island we were camping on, in Haliburton, Ontario this past weekend. There were sometimes as many as 4. Every time one arrived or left, they greeted each other with a wee wee wee wee wee wee, kind of a small sound for a bird the size of a crow.