CHANGES IN THE WINTER DISTRIBUTION OF THE ROUGH-LEGGED HAWK 
Figure 7. Average numbers of the Rough-legged Hawk (RLHA) and Red-tailed 
Hawk (RTHA) per 100 party hours and number of December days with snow cover 
in excess of 5 cm in four successive 7-year periods (1, count years 79-85; 2, count 
years 86-92; 3, count years 93-99; 4, count years 100-106) for the North and 
South Plains regions. 
regions the Rough-legged Hawk declined, and in the Atlantic Coast region 
its abundance in the later 14-year period (2 birds/100 party hours) was 
the lowest of any region. In both regions days with significant snow cover 
remained relatively stable, with only a slight increase in snow cover for the 
last two 7-year periods for the Atlantic Coast. Human population growth 
in the counties associated with the CBC circles in both regions was low (8% 
for the East; 15% for the Atlantic Coast). 
DISCUSSION 
Christmas Bird Counts reveal changes in the winter distribution of the 
Rough-legged Hawk throughout its North American range. Ranges and 
migration dates of many species are changing in response to climate change 
(Moller et al. 2004, Schneider and Root 2002, Niven et al. 2009, Kim et 
al. 2009), and this northward shift in the Rough-legged Hawk’s distribution 
is consistent with many other bird species in North America (Niven et al. 
2009). 
Logistic regression showed no significant effect of average December 
temperature on Rough-legged Hawk abundance. For snow cover (December 
days with cover >5 cm), however, the effect was negative and significant (P 
< 0.001). It is not surprising that Rough-legged Hawks might remain farther 
north or shift their wintering range to the north in response to less snow 
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