Foraging Behavior of Northern Harriers Wintering in Southeastern Salt and Freshwater Marshes

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Abstract
We conducted a comparative study of the foraging behavior, hunting success, and diet of wintering Northern Harriers (Circus cyaneus) at North Inlet Marsh, a salt marsh in South Carolina, and Paynes Prairie, a freshwater marsh in Florida. The relative use of five hunting methods in the salt and freshwater marshes differed significantly (P < 0.0005). Harrier rates at Paynes pouncing Prairie were three times greater than at North Inlet Marsh, but their hunting success was significantly less (5.8% vs. 15.1%, P < 0.0005). Greater capture success at North Inlet Marsh was caused by differences in diet and vegetation structure rather than by differential use of hunting techniques. Harriers hunting at North Inlet Marsh captured exclusively birds, whereas at Paynes Prairie harriers captured primarily cotton rats (Sigmodon hispidus). Although differences in pouncing rate, capture success, and diet occurred between the two study areas, prey capture rates at North Inlet Marsh (27 g/h) and Paynes Prairie (23 g/h) were similar. Our findings that harriers had higher capture success hunting small- and medium-size birds on a salt marsh than cotton rats on a freshwater marsh contradicts the generalization that more mobile prey are more difficult to capture and illustrates the importance of comparative foraging studies.

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