_Winter._--The Arctic three-toed woodpecker is normally mainly resident in winter throughout most of its breeding range; it is a hardy bird and its food supply is available at all seasons, the grubs on which it feeds remaining in the wood for more than one season. Probably a few wander southward nearly every winter, and there have been several heavy flights of these birds into the Northeastern States, which it is not easy to explain. Dr. Josselyn Van Tyne (1926) has given a full account of one of these invasions, to which the reader is referred. Mr. Forbush (1927) writes: It is difficult to determine exactly what causes these unusual migrations, They are not forced by inclement weather, for one at least has occurred in a mild winter. * * * It seems probable that the unusual invasions of the species into New England follow summers when its food has been unusually abundant. An excessive food supply tends to fecundity, and overbreeding naturally compels expansion and induces migration, whether among the lower animals or humankind. Since the above was written, Mr. Josselyn Van Tyne has published a paper regarding the unusual flight of this species in 1923 in which he advances a similar explanation. He says that between 1909 and 1914 there was an irruption of the spruce budworm in eastern Canada and Maine which resulted in the death of many trees and a consequent increase of bark-beetles and borers, followed by an increase in the number of these woodpeckers. On the other hand a scarcity of the usual food supply may cause migration. A wet season with few fires in the woods or a scarcity of insects (such as the spruce bud-moth) that kill trees might, later, cause a migration. Illustrating the length of the sojourn of these woodpeckers during the winter of 1923-24, Dr. Van Tyne (1926) says: The greatest concentration of these woodpeckers recorded at any one point was on the estate of Mr. F. H. Kennard where scores of dead and dying white pine afforded an abundance of their special food. The first one seen was a male collected on October 17. Another individual appeared by October 20 and during the winter at least three males and two females were accounted for, while all indications point toward the actual presence of perhaps twice as many. The most remarkable fact about this group of birds, however, was the length of their stay, for both males and females were seen as late as the middle of May and at least one male stayed through the early part of June and was last seen on June 12.