CHANGES IN THE WINTER DISTRIBUTION OF 
THE ROUGH-LEGGED HAWK IN NORTH AMERICA 
EDWARD R. PANDOLFINO, 5530 Delrose Court, Carmichael, California 95608; 
erpfromca@aol.com 
KIMBERLY SUEDKAMP WELLS, ENVIRON International Corporation, 3019 Miller 
Road, Ann Arbor, Michigan 48103 
ABSTRACT: We used Christmas Bird Count (CBC) data to demonstrate a shift in the 
winter distribution of the Rough-legged Hawk ( Buteo lagopus) in North America from 
the late 1970s to the early 2000s. Data from nearly 300 CBC circles reveal decreases 
in the Rough-legged Hawk's abundance on the east and west coasts and throughout the 
southern portion of this species’ winter range. Its abundance increased in the northern 
portions of the Great Plains. This distributional shift was associated with a decrease in 
the number of December days with substantial snow cover in the northern Great Plains 
and an increase in the winter abundance of the Red-tailed Hawk ( Buteo jamaicensis ) 
throughout most of the range of the Rough-legged Hawk. In addition, increasing human 
populations and associated loss of open country may have contributed to this shift. 
The Rough-legged Hawk ( Buteo lagopus ) is a holarctic breeder that, in 
North America, winters from southern Canada through all but the most 
southerly parts of the continental United States (Johnsgard 1990, Bechard 
and Swem 2002). On the basis of Christmas Bird Count (CBC) data from 
1962 to 1972, Root (1988) showed that its main areas of winter abundance 
were the northern Great Basin and the Great Plains from western Kansas to 
eastern Montana. The northern limit of the winter range seems determined 
by climate (Bock and Lepthien 1976, Root 1988, Olson and Arsenault 
2000), while it is unclear what factors determine the southern limit. 
Although there are no obvious continent-wide trends in breeding or win- 
ter populations of the Rough-legged Hawk in North America (McCay et al. 
2001, Bechard and Swem 2002), from the late 1980s into the late 1990s 
local declines were reported from New Jersey (Walsh et al. 1999), Delaware 
(Hess et al. 2000), Colorado (Schmidt and Bock 2005), and California (Pan- 
dolfino 2006). To determine if these local changes represent a widespread 
phenomenon, we examined CBC data from throughout the Rough-legged 
Hawk’s North American winter range over roughly the past three decades. 
We examined climate data, changes in Red-tailed Hawk abundance, and 
trends in the human population (possibly an indicator of habitat loss) to 
assess possible effects of these factors on the Rough-legged Hawk’s winter 
distribution. Winter temperature and/or snow cover can affect the Rough- 
legged Hawk’s distribution (Root 1988), movements (Theil 1985, Watson 
1986a), and behavior (Schnell 1968, Klein and Mason 1981, Temeles and 
Wellicome 1992, Watson 1986b, Lingle 1989), and the Red-tailed Hawk is 
a documented interspecific competitor (Schnell 1968, Bildstein 1987). 
METHODS 
CBC Data 
We obtained CBC data from the National Audubon Society’s database 
(www.audubon.org/bird/cbc/hr/index.html). For all analyses we used the 
210 
Western Birds 40:210-224, 2009 
