Common Redpoll

Common Redpolls are a classic “winter finch,” and typically show a biennial cycle with high numbers one year followed by almost none the next. The peaks are called “irruptions” and result when birds’ food supplies in their regular winter range are low, thus forcing them to move elsewhere in large numbers in search of better feeding grounds. For Common Redpolls, the drivers of the irruptions are spruce and birch seed crops in boreal Canada and Alaska where the species nests. These trees typically produce bumper crops every other year, and in the off years we expect the birds to show up much farther south – such as in the northeastern United States. Although this pattern is pretty consistent in the data shown here, there are also obvious deviations, and the cause of these is entirely unknown.

Because they nest in the far north (often near treeline) where there are few observers, studies on the breeding grounds are few. This makes it difficult to assess population trends, but the scant data available suggests that redpolls are decreasing. We still don’t have a good idea why (again, no studies!), but it’s possible that the lower irruptive peaks in recent years are one manifestation of a declining population.

When there is a redpoll invasion, birders are always on the lookout for a closely related species of northern finch: the Hoary Redpoll. These two are extremely difficult to tell apart, and some biologists even think they’re the same species. Hoaries are much rarer than Commons, perhaps no better than one in a hundred, and you need a very good view to be sure you have one. Important features include bill shape and undertail streaking, and be sure to have a camera and field guide handy.