Degree Name

Master of Science (MS)

Semester of Degree Completion

1998

Thesis Director

Eric K. Bollinger

Abstract

I studied habitat selection and reproductive success of a migratory population of Loggerhead Shrikes (Lanius ludovicianus migrans) as well as the temporal and spatial patterns of impaling exhibited by this population during the nesting season. The selection of breeding habitat was investigated at different spatial scales. Thirty-eight (67%) of 57 nests were located in osage orange (Maclura pomifera) trees. Shrike territories (area ≤ 200 m from nest site) contained significantly more pasture, fenceline, and perch sites, but less com, alfalfa, and forest than random sites. At larger spatial scales, more grassland was detected within 300 m of shrike nests than random locations. However, no differences were detected between shrike nests and random sites when larger radii (600, 900, 1500 m) were analyzed. Nest success (49%) and productivity (3.63 young/pair) were similar to North American averages, and habitat variables appeared to have little influence on nest success. However, nests located along roadways were significantly less successful (35%) than interior nests (70%).

I detected impaled prey on 88% of 24 breeding territories searched, with an average of 1.77 items found per search. Insects and reptiles were the most common taxa impaled comprising 56% of all items detected. Honey locusts (Gleditsia triacanthos) were the most frequently used impaling substrate holding 67% of all items. Abundance of impaled prey was highest during the nestling stage (2.24 ± 3.40 items/search), and shrikes impaled significantly closer to the nest during this stage (18.13 ± 11.02 m) than during either the incubation (31.13 ± 12.2 m) or fledgling (25.03 ± 8.08 m) stages. Finally, a significant positive correlation was observed between the abundance of impaled prey and reproductive output of successful nests. These results suggest that energy demand was an important factor affecting impaling patterns, and supplemental food delivery to incubating females and nestlings was a primary function of impaling during the nesting period.

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