Browsing by Author "McGowan, Conor Patrick"

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Factors affecting nesting success of American Oystercatchers (Haematopus pallitus) in North Carolina.
(2004-04-08) McGowan, Conor Patrick; Jaime Collazo, Committee Member; Ken Pollock, Committee Member; Theodore R. Simons, Committee Chair
American Oystercatchers are listed as a 'Species of High Concern' by the U. S. Shorebird Conservation Plan, in part because of threats during the breeding season. Oystercatchers nest on the sandy beaches of the East Coast of the United States and their nesting habitat is under increasing threat from human development and human disturbance. In this study, I analyzed 8 seasons of reproductive success data for American Oystercatchers in North Carolina. I identified the primary causes of nest failure and I examined spatial and temporal patterns of hatching success. Hatching and fledging success were very low, but highly variable among years and locations. Mammalian predation accounted for 29% of nest failures, and mammalian predator control would likely increase reproductive success of American Oystercatchers. I looked closely at the relationship between human disturbance and hatching success. Previous studies at Cape Lookout National Seashore showed that there were negative temporal and spatial associations between human disturbance and oystercatcher nesting success. I measured human disturbance three different ways; daily nest checks, beach surveys of human presence, and video monitoring at oystercatcher nests. I used logistic regression and 2x2 contingency table analyses to test for associations between higher levels of human disturbance and lower hatching success. Contingency table analyses of the daily nest check method showed that higher levels of human disturbance were associated with lower hatching success. There were no associations between human disturbance and nesting success for the other two measures of disturbance, but the analyses were constrained by small sample sizes and lack of information on the distances to sources of disturbance. I also tested the hypothesis that parental incubation behavior was a mechanism through which human disturbance lowered hatching success. I used video monitoring to record the behavior of American Oystercatchers during incubation. I calculated the rate of trips to and from the nest, and rate of movements while incubating, and the percent of time spent incubating. I assigned a cause for each trip away from a nest. Twenty-four percent of trips were associated with ATVs, 17% with trucks, 3% with pedestrians, 8% with territorial fighting, and 18% with exchanging incubation duties. I used linear regression to test for correlations between human disturbance and incubation behaviors. I also used logistic regression and 2x2 contingency table analyses to test for associations between varying levels of human disturbance and hatching success. Human disturbance, especially ATV traffic, was associated with more trips to and from nests and less time spent incubating. More frequent trips to and from the nests were associated with lower hatching success. It is probable that human disturbance reduces oystercatcher hatching success by increasing the activity of incubating adults.