Arthur M. Martell
Comox Valley Naturalists Society, Box 3222, Courtenay, B.C. V9N 5N4; e-mail: amartell@shaw.ca
Abstract: Changes in numbers of birds in the Comox Valley, British Columbia, from 1976 to 2006 were examined based on two counts each year, conducted in May and December, in the Comox Christmas Bird Count circle. A total of 44 species of coastal birds (coast/wetland habitat) and 58 species of upland birds (forest/woodland, scrub/successional, grassland and suburban/urban habitats) were reported sufficiently frequently for analysis. The trends are discussed in relation to the North American Breeding Bird Survey counts and to climate change.
Coastal birds showed a much greater tendency to population decrease and a lesser tendency to population increase than upland birds. Coastal birds tended to be significantly more abundant in winter than in spring and 34% of the species showed significant positive trends and 25% of the species showed significant negative trends on one or both counts. Harlequin Duck showed a significant decline in spring but not in winter. However, the numbers in both seasons decreased from 1976 to the mid-1990s and then increased. Western Grebe showed significant declines on both counts; examination of the annual numbers showed a great variability among years on both counts, but clear declines to the late 1990s and a possible slight recent recovery in numbers. Bald Eagle showed significant, steady increase in numbers on both counts.
Almost half of the species of upland birds (46%) showed significant positive trends on one or both counts and only 10% showed significant negative trends. Differences by migration status were pronounced, with only 19% of 16 neotropical migrants showing significant positive trends compared with 57% of 42 short-distance migrants and residents combined; the proportion of species showing significant decreasing trends was similar (12% and 10%, respectively). Most of the species of upland birds that showed an increasing trend are species that concentrate in winter (sparrows, blackbirds, urban/suburban birds). Bewick’s Wren, aerial foragers (Violet-green Swallow, Barn Swallow) and finches (Purple Finch, Evening Grosbeak) showed significant negative trends and are of particular concern.
Key words: Comox Valley, population trends, Christmas Bird Count, spring migration, climate change, waterfowl, waterbirds, shorebirds, landbirds, Harlequin Duck, Histrionicus histrionicus, Western Grebe, Podiceps occidentalis, Bald Eagle, Haliaeetus leucocephalus, Bewick’s Wren, Thryomanes bewickii, Violet-green Swallow, Tachycineta thalassina, Barn Swallow, Hirundo rustica, Purple Finch, Carpodacus purpureus, Evening Grosbeak, Coccothraustes vespertinus
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