Irruptions
Common Redpoll

The term "irruption" refers to the movement of a species (or several species) from an area where they typically occur into a region where they are not normally present. The most common irruptions in North America are of winter finches. These birds, which include Common Redpolls and White-winged and Red Crossbills, normally winter in Canada but sometimes irrupt into the United States during the winter.

The map above shows the distribution of Common Redpoll in February during a non-irruptive year, 1996-97. Based on reports from Project FeederWatch, this interpolated surface shows higher abundance in darker shades of green. The map below shows the distribution of Common Redpoll in February during an irruptive year, 1997-98. Note the expansion of birds into the northeastern U.S. and southern Canada. 1997-8.

The regularity of Common Redpoll irruptions can be seen in the animated map below.
Learn more about winter finch irruptions by visiting the
Irruptive Bird Survey site

When many species irrupt during the same year, it is called a "superflight." To learn more about superflights, visit the 1997-98 North American Winter Finch and Red-breasted Nuthatch Survey site.

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