In the 1990s, research indicated that Jericho Bay was the single largest wintering location for Harlequin Ducks in Eastern North America, but the latest research suggests this is no longer the case.

In 1988, Glen Mittelhauser started a distribution and winter ecology study of Harlequin Ducks on Isle au Haut. That research showed that the area from Isle au Haut and Northeast to Swans Island was the single largest wintering location for Harlequin Ducks in Eastern North America where it was typical to see over 200 individuals in a day.

Glen surveying Harlequins on Isle au Haut.
(Photo by Logan Parker)

Starting in 2023, Glen and his team set out to repeat those earlier surveys and have already found significant changes from 30 years ago. There are significantly fewer Harlequin Ducks – around 70-80 reported for every survey. Harlequin Ducks are extremely site faithful, returning not just to the same island but to the same side of that island to winter year after year. Glen’s team is still trying to unravel this change but it seems that either the ducks are not returning to the area because of mortality or are changing their wintering grounds – which would be a significant behavioral shift for this species! What we do know is that the wintering Harlequin Duck population is increasing further Downeast but the cause of this change is still to be unraveled.