. The Canadian field-naturalist. 44 The Canadian Field-Naturalist Vol. 94 ^^KOM m ⢠-1 No. of occurrences ⢠â 2-6 ⢠-7-12 193 0 kn â »â > normal range O I hypothetical. ^^SK -N- man ONT ^SMB Figure 1. Extralimital occurrences of Clark's Nutcracker in Canada to 1976. The differently sized dots indicate the total number of occasions on which nutcrackers (groups as well as single birds) have been recorded at each site. The normal range includes breeding range plus the lower elevations regularly visited in autumn and winter altitudinal migrations (from Godfrey 1966 for Canada and Skaar 1975
. The Canadian field-naturalist. 44 The Canadian Field-Naturalist Vol. 94 ^^KOM m ⢠-1 No. of occurrences ⢠â 2-6 ⢠-7-12 193 0 kn â »â > normal range O I hypothetical. ^^SK -N- man ONT ^SMB Figure 1. Extralimital occurrences of Clark's Nutcracker in Canada to 1976. The differently sized dots indicate the total number of occasions on which nutcrackers (groups as well as single birds) have been recorded at each site. The normal range includes breeding range plus the lower elevations regularly visited in autumn and winter altitudinal migrations (from Godfrey 1966 for Canada and Skaar 1975 for Montana). The "hypothetical range" is based on an unpublished report from A. J. Erskine and two records in Munro(1947). The Canadian distribution of Whitebark Pine is adapted from Hosie (1969). The solid dot in the Alaska Panhandle represents two observations at Sitka in August 1866 and March-April 1933 (Gabrielson and Lincoln 1959). viduals recorded in August through November prob- ably underestimate the virtual exclusiveness of the fall as the time for eruptive dispersal. For Alberta 70% of the birds were observed in August and September, while in British Columbia 60% were recorded in October and November. The six Yukon observations are inconclusive, ranging from April to August (Table 1), which could indicate local breeding there, but seven of eight records from Alaska range from August to November (Gabrielson and Lincoln 1959; Gibson and Byrd 1973), indicating late summer eruptive dis- persal from British Columbia. The largest monthly mean flock sizes (excluding June because of only one observation then) occurred in August () and September () (Figure 2). There was a wide variation in group size (2-30), but the largest flocks of extralimital nutcrackers were record- ed in Alberta not far from the normal range (Fisher 1979). Single birds were involved in 70% of the records. 2. Synchrony and Regularity In the autumn of 1919 extralimital occurren
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