CHANGES IN THE WINTER DISTRIBUTION OF THE ROUGH-LEGGED HAWK 
Plains region they increased (36/43, 84%). Similarly, when counts are 
pooled by region, Rough-legged Hawk numbers decreased in the western- 
most, easternmost, and southern regions but increased in the North Plains 
(Table 1). The North Intermountain West and the two Great Lakes regions 
showed decreases that were not statistically significant. The results of linear 
regression by region (Figure 2) were qualitatively identical, with negative 
trends for the southern and coastal regions and a strong positive trend for 
the North Plains. 
Logistic regression of the change in the Rough-legged Hawk versus single 
predictor variables indicated there were statistically significant negative effects 
on the abundance of the Rough-legged of the abundance of the Red-tailed 
(coefficient = -1.90 ± 0.38, P < 0.001; odds ratio = 0.15, 95% confidence 
interval 0.07-0.32; n = 293) and of an increase in the number of December 
days with snow cover >5 cm (coefficient = -0.19 ± 0.05, P < 0.001; odds 
ratio = 0.83, 95% confidence interval 0.75-0.92; n = 199). Increase in 
human population had a significant negative effect on Rough-legged Hawk 
abundance (coefficient = -1.12 ± 0.54, P = 0.04; odds ratio = 0.33, 95% 
confidence interval 0.11-0.94; n = 245). Changes in average December 
temperature had no significant effect (coefficient = 0.14 ± 0.11, P = 0.21; 
odds ratio = 1.15, 95% confidence interval 0.92-1.44; n = 262). 
Pacific Coast Regions 
In the Pacific Coast regions Rough-legged Hawk abundance was relatively 
low while Red-tailed Hawk abundance was relatively high (Figure 3). The 
South Pacific Coast had the highest Red-tailed Hawk abundance of any 
region with numbers consistently over 130 birds/100 party hours. Red- 
tailed Hawk numbers in both Pacific Coast regions were relatively stable, 
in contrast to the increases seen in nearly every other region. As snowfall 
was generally light to none in these regions, snow cover was not a factor 
Table 1 Changes in Numbers of the Rough-legged Hawk (per 100 Party 
Hours) on Christmas Bird Counts in Ten Regions of North America. 
Region 
Count years 
79-92 
Count years 
93-106 
Change 
P a 
CBCs (n) 
N. Pacific Coast 
8 
4 
-50% 
<0.001 
15 
S. Pacific Coast 
6 
2 
-59% 
0.003 
10 
N. Intermountain West 
43 
34 
-22% 
NS b 
35 
S. Inter mountain West 
24 
11 
-54% 
0.002 
16 
N. Plains 
13 
21 
60% 
<0.001 
43 
S. Plains 
13 
9 
-32% 
0.002 
27 
W. Great Lakes 
10 
9 
-12% 
NS b 
53 
E. Great Lakes 
8 
7 
-12% 
NS b 
50 
East 
12 
6 
-49% 
<0.001 
27 
Atlantic Coast 
8 
3 
-64% 
<0.001 
17 
All 
13 
10 
-20% 
NS b 
293 
“Paired t test. 
fa Not significant, P > 0.005. 
214 
