REPRODUCTIVE SUCCESS AND TERRITORY RE-OCCUPATION RATES FOR RED-SHOULDERED HAWK 
(BUTEO LINEATUS) WITHIN THE MILAN BOTTOMS. 

Jon W. Stravers1, Kelly J. McKay2 , and Gary Swenson3.
1National Audubon Society, Upper Mississippi River Campaign, McGregor, IA 52157,
2Midwest Raptor Research Fund, Hampton, IL, 3U.S. Army Corps of Engineers 
Natural Resources Management Section, Rock Island District.

Between 1992 and 2002, we collected information on Red-shouldered Hawk (Buteo 
lineatus) nesting within the Milan Bottoms study area which includes 
approximately 1300 acres of bottomland forest and wetland habitat along the 
Mississippi River just below the confluence of the Rock River in Rock Island 
County, Illinois. The study area is managed by the U.S. Corps of Engineers 
Natural Resources Management Section, although some of the perimeter habitats 
are in private ownership. 

The number of nesting attempts we confirmed varied from year to year. We 
confirmed three attempts in 1998, 1999 and 2000, and two attempts in 2001 and 
2002. We confirmed a total of 26 Red-shouldered Hawk nesting attempts between 
1992 and 2002, and we were able to determine the outcome of 22 attempts.   Of 
these, 12 were successful (57.1%), and 21 nestlings reached fledging age (1.75 
per successful nest and 0.95 per nesting attempt).  This success rate is 
slightly lower than the average rate we found at the other known Red-shouldered 
Hawk nesting sites along the Mississippi River between 1983 and 2002.  During 
that period, we determined the outcome of 106 Red-shouldered Hawk nesting 
attempts (average of 5.3 per year). Of these, 69 were successful (65.1%) and 153 
nestlings reached fledging age (average of 2.22 per successful nest, or 1.44 per 
nesting attempt). Success rates varied from year to year, with a high of 88% to 
a low of 33% during the flood years of 1993 and 2001.

Red-shouldered Hawk nesting sites were usually located in mature or medium aged 
forests and most of the nests were situated within 100 meters of a waterway or 
slough.  Most nests were placed in areas where the overhead forest canopy was 
well developed.  Active nests were placed in Silver Maples (Acer saccharinum) 
(78%), Eastern Cottonwood (Populus deltoides) (14%), and in Green Ash (Fraxinus 
pennsylvanicus) (8%). The diameter at breast height of the nest trees ranged 
from 16.9" to 32.6".

During the course of this study we have found that 89% of Red-shouldered Hawks 
breeding territories that we monitored along the Mississippi River were active 
in subsequent years.  Because of this nest-site tenacity, we feel this species 
is an excellent “Umbrella Species” - an indicator of high quality habitat. 
Management practices that favor Red-shouldered Hawks are likely to benefit 
several species of concern that require large unfragmented forest tracts, 
especially some of the neotropical migrant passerines which may be more 
difficult to monitor.

Keywords:  Red-shouldered Hawk, Buteo lineatus, Upper Mississippi River, raptor 
monitoring, floodplain forests.