With birders now doing Christmas Bird Counts, here is an important study
using CBC data just published in the 104th Christmas Bird Count (2003-2004)
issue of American Birds. It has an article by Nick Bolgiano titled "Cause
and Effect: Changes in Boreal Bird Irruptions in Eastern North America
Relative to the 1970s Spruce Budworm Infestation". The most recent budworm
infestation of 1968-1985 defoliated approximately 55 million hectares
(about 140 million acres) across Ontario, Quebec and the Maritime
Provinces. To get an idea of the size of the infestation, it was about as
big as the combined area of New York, Pennsylvania, Maryland, West
Virginia, Virginia, and North Carolina. Using CBC data, Bolgiano found
changes in irruption patterns of seven species: Evening Grosbeak, Purple
Finch, Black-capped Chickadee, Boreal Chickadee, Pine Grosbeak, Red
Crossbill, and White-winged Crossbill. Birders know about the rise and fall
of the budworm warblers (Tennessee, Cape May, Bay-breasted), but this study
emphasizes that "an understanding of population trends of many of eastern
North America's boreal birds must include the role of the 1970s budworm
infestation." Bolgiano asks if the 1970s infestation contributed to the
general declines of neotropical migrants in the 1980s and concurrent
decline of the Sharp-shinned Hawk. He ends by saying that the Christmas
Bird Count and Breeding Bird Survey have informed us that the spruce
budworm event of the 1970s apparently had a major impact on boreal forest
bird populations. I recommend that you read the entire article for its full
meaning. The author acknowledges the help of Canadian birders and
ornithologists and three Ontario Ministry of Natural Resources foresters.
If you don't have this issue of American Birds, perhaps you could borrow it
from your CBC compiler or from a member of Bird Studies Canada.
This 128 page issue also has several other informative articles and the
regional summaries of last year's 104th Christmas Bird Count, including the
Ontario report by Sarah Rupert.
Reference: Bolgiano, Nicholis C. 2004. Cause & Effect: Cause and Effect:
Changes in Boreal Bird Irruptions in Eastern North America Relative to the
1970s Spruce Budworm Infestation. American Birds 58: 26-33. This article is
in The 104th Christmas Bird Count 2003-2004. Volume 58. 128 pages. American
Birds. Published by the National Audubon Society in association with the
Audubon Science Center and Bird Studies Canada.
Ron Pittaway
Ontario Field Ornithologists
Minden and Toronto
jeaniron AT sympatico.ca
