This large finch breeds in coniferous or mixed coniferous/deciduous forest, usually near openings, with the nest near the trunk from 5-35 m above ground level [Bekoff et al. 1989]. It is single-brooded, feeding on insects (particularly spruce budworm), buds, berries and seeds [Gillihan and Byers 2001 (BNA)]. Breeding range is in the conifer belt from southeast Yukon and Vancouver Is. east to south Newfoundland and northern Maine; also south in conifers in the western mountains, discontinuously to north California, through Colorado, New Mexico, and in montane Mexico south to Oaxaca [Gillihan and Byers 2001]. The winter range includes the breeding range (though northern birds often move south), but varies greatly with food supply and hence irruptive movements. Evening Grosbeaks have been recorded in winter in all 48 contiguous U.S. states [Gillihan and Byers 2001 (BNA)]. Winter food from trees and shrubs includes berries, deciduous and coniferous seeds of a wide range of species [Gabrielson 1924, Speirs 1968], and particularly in New England, sunflowers and other bird feeder fare.
Evening Grosbeaks move in diurnal flocks, perhaps also at night [Speirs 1968]. Males in the east U.S. move shorter distances in winter, females further south, although the reasons for this are not clear, and western populations are more sedentary [Gillihan and Byers 2001 (BNA)]. Wintering birds depart for the breeding grounds by early to mid-May in New England, and return from early September to the end of October in irruption years [Shaub 1960]. Three to four weeks before breeding, flocks break up into smaller groups, and mated pairs are formed before arrival on the breeding sites [Magee 1934].
The breeding range has expanded east, Evening Grosbeaks being considered rare east of the Rocky Mts. until the mid-1800's [Cassin 1858]. During the winter irruption of 1889-1890 they reached New York and New England, the numbers of breeding pairs expanding greatly in New England only as lately as the early 1940's to mid-1950's [Gillihan and Byers 2001 (BNA)]. The eastern expansion was commonly attributed to a persistent winter food supply of box elder (Acer negundo) seeds, as this tree was commonly planted as prairie windbreaks and in ornamental gardens [Forbush 1929]. From 1980-1999, the Breeding Bird Survey shows recent, rapid and widespread declines in all areas averaging -5.3% per year, for unknown reasons [Sauer et al. 2000].
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Observations
This winter resident can be common in the study area during irruption years, but breeds well to the north. Evening Grosbeaks were significantly more abundant in C sites (376/423 records) away from the rivers. State differences were also significant, despite (or perhaps because of) the lack of a major irruptive winter during the three years of our study. Thus numbers decreased from a maximum total of 249 records in VT, 124 in NH, 41 in MA, to 9 in CT.
Although the period differences in density were not statistically significant, it is noteworthy that more than half the records (259/423) were in periods 1 and 2. This is a flocking species on migration, the largest transect count being 31 birds in period 2 at a C site in VT. |
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