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The Importance of Canada's Boreal Forest to Landbirds

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PART 2: HOW SIGNIFICANT ARE BOREAL LANDBIRDS THROUGHOUT CANADA, NORTH AMERICA AND THE WESTERN HEMISPHERE?

2. e. How significant are these migrants to the avifauna of other countries?

This analysis focuses on the United States, as there are several good datasets from which to estimate proportions of boreal migrants among all birds surveyed.³ Below are the results from the three datasets used for this report

1) The Gulf Coast Bird Observatory network for spring and fall migration (http://www.gcbo.org/) provides a useful dataset because it includes over 45,000 single day counts collected across a broad front of several states north of the Gulf of Mexico (Figure 6). Data were filtered to include counts only during periods of spring and fall migration (from March 20 to June 1, and from July 15 to October 31). This network detects mainly landbird species.

Figure 6: GCBO sample sites for spring and fall migration

2) Christmas Bird Count data from the contiguous U.S. (48 states) for 1990 to 1998 were also analysed. These data are the result of one day counts of all species observed within a 24-km (15-mile) diameter circle. Abundance indices were weighted among states by area covered.

3) Project FeederWatch data from 1997 to 2001 were also examined. For this comparison, statewide geometric mean abundance indices have been used as a measure of relative abundance of each species at feeders within the lower 48 states. Weighting of indices across states in the U.S.A. was done on the basis of number of feeder stations reporting in each state, on the assumption that this is reasonably proportional to interest in bird feeding in the various states.

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³The proportion of birds originating from Canada's boreal forest was estimated by calculating the number of boreal migrants that leave Canada (boreal migrants as in Tables 6 & 7 minus migrants remaining in non-boreal Canada, Table 9), and then dividing by the total numbers of birds (migrants or not) in the United States. This method was applied against three datasets.

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