Courtship

As far as we are currently aware, the members of loon pairs do not spend the winter together. They typically migrate separately in the fall, winter separately, and then arrive back to breeding lakes at different times (the males tend to arrive a bit earlier than the females).

Because they don't spend the winter together, when members of a pair arrive on their breeding lake, they have to re-establish their pair bond (or, if those particular individuals have not been a pair in the past, establish their pair bond for the first time). Loons are monogamous, and due to their high territory fidelity (the tendency to return to the same breeding lake each year, especially if they've fledged chicks from that lake in the past), there is a good chance that the same loons are making up the pair year after year. However, loons do not mate for life. If a member of the pair dies or is evicted from its territory by an intruding loon, the remaining pair member will accept a new mate.

--shared courtesy of Loon Preservation Committee