We often see them in the winter months (or when they are migrating?) in Mattpoisett, MA. Their white feathers disappear and they are very dark in color.
More about Loon Migration I've also been up at the cottage during ice-out in April (It'll be April 24th is year for sure at 7:30 a.m.

) and a flock (or is it a herd?) of loons have shown up only a few days later. How do they know the open water has arrived? Here's a shot I took on 4-26-03 noting that the ice had only gone out the day before.