The ecology of red -tailed hawks and red -shouldered hawks in forested landscapes and in landscapes fragmented by agriculture

Joelle Lynn Gehring, Purdue University

Abstract

Habitat alteration and loss have contributed to the decline in populations of several woodland raptors that once inhabited most of Indiana. When forests are fragmented, these area-sensitive raptors potentially experience increased disturbance from human activity, decreased availability of nesting sites, lower prey availability and diversity, increased competition for resources, and lowered nest productivity. The Red-shouldered Hawk (Buteo lineatus ) was once the most common hawk in eastern North America; however, it is now considered to be a rare and declining species throughout most of its range. Several observers have reported that larger, more generalist, Red-tailed Hawks (Buteo jamaicensis) displace Red-shouldered Hawks from forested nesting areas. I found that nest success was significantly different between these two raptor species and among areas with different levels of forest fragmentation. Red-tailed Hawks had the highest nest survival in the forested landscape whereas nest survival of Red-tailed Hawks in the most fragmented areas was significantly lower. Red-shouldered Hawks in the continuously-forested landscape had the lowest nest survival. Based on landscape-level habitat variables, I developed models that predicted the presence of nest site areas of both raptor species in habitats with varying amount of fragmentation. I also compared the two species food habits, food niche breadth, niche overlap, and nesting behavior. Red-tailed Hawks tended to consume mammals and snakes, whereas Red-shouldered Hawks consumed amphibians and invertebrates, in addition to mammals and snakes. Food niche overlap between the two hawk species was greater in the most contiguously-forested site than in the moderately fragmented site. Radio-telemetry data from Red-tailed Hawks in fragmented sites suggest that the proportion of agricultural row-crop fields in the landscape is positively related with home-range size. The flight behavior of Red-tailed Hawks is of particular interest because of their frequent collisions with military aircraft. I found significant relationships between Red-tailed Hawk flight altitude and corresponding temporal, spatial, and weather variables. I developed predictive models for flight altitude based on these variables. These models may be used to improve Bird Avoidance Models for the U.S. Air Force.

Degree

Ph.D.

Advisors

Weeks, Purdue University.

Subject Area

Forestry|Ecology|Environmental science

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