The Common Loon is a migratory bird that winters in warmer regions and returns to its breeding lakes in the spring  Typically, only one pair of loons occupies a single lake  Breeding pairs in search of breeding territory either occupy a vacant lake or take over an already occupied one  Surprisingly, almost half the time, returning loons choose to intrude on a territory already occupied by another pair of loons and attempt to oust its residents
This happens even when there are vacant lakes nearby that are perfectly suitable breeding territories
Loons that intrude on an occupied breeding territory are successful in ousting its residents about half the time.