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Absent winter visitors

For many years I have had bird feeders on my deck offering black sunflower seeds, suet, peanuts and niger seeds in both winter and summer, always on the lookout for the unusual migrant arrival. This winter things have been pretty mundane. Although the number of birds has been about normal, variety has been lacking. Nuthatches (both), woodpeckers (hairy and downy), chickadees, goldfinch, purple finch, bluejays, a few tree sparrows, an occasional junco, and a couple of mourning doves have been about the whole list except for a dwindling flock of wild turkeys and one ruffed grouse. All of these species are year round residents of the area. Disappointingly absent this year have been any sightings of redpolls or evening grosbeaks. A little research reveals two different scenarios for the missing birds. The redpoll is an inhabitant of the far northern boreal forests and breeds even farther north in arctic regions. Relatively little is known about population trends because of the remote area it inhabits. The redpoll irrupts regularly on a two-year cycle into the northern US and across Canada, driven south by a scarcity of the seeds it depends on in winter, particularly birch, willow, alder, and various conifer trees (especially spruce). A check of Christmas Bird Count records for my local count circle confirms this cycle: even numbered years from the mid-nineties to the present show high numbers (100-400 birds) while odd numbered years have from zero to less than a dozen redpolls. The brightly colored evening grosbeak inhabits a large area of the western US extending south into Mexico. It moved eastward above the great Lakes and along the Canada-US border to the Atlantic coast only during the 1900s. The evening grosbeak also is driven south by seed crop shortages and in the 70s and 80s was a common winter feeder visitor in the northeast. A flock of evening grosbeaks would clean out a sunflower feeder in an hour or so, but this has not been a common occurrence in recent years. Vermont Christmas Bird Count numbers for evening grosbeaks in the eighties and early 90s are in the thousands (high of 7179 in 87) but since the late nineties have been only a few hundred, with a low of only 57 birds in the early 2000s. Scientists believe the evening grosbeak expanded into the east as result of an increased availability of the box elder. This tree was widely introduced as an ornamental planting in many cities, has many seeds, and retains these seeds into the winter. Another enticement for the grosbeak was the spruce budworm. Some studies show that the evening grosbeaks breeding presence in a new area can signal an impending spruce budworm outbreak before any forest damage is evident! Perhaps the spraying of the budworm has controlled the insect but shrunk the grosbeak population to pre-expansion levels? Next year I expect the redpoll will be more numerous but the evening grosbeak will probably remain a scarce sighting in this part of the country for some time to come.

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