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Mallard Recruitment in the Agricultural Environment of North Dakota

Capture and Radio Marking

Hens (N = 338) were captured with rocket-projected nets at baited sites on small ponds, or with a shoulder-held net-firing gun (Mechlin and Shaiffer 1980). Birds were banded with USFWS aluminum bands. Hens were weighed and measurements were taken of length of wing chord for calculation of a condition index. Secondary coverts 2 and 3 were pulled for later use in age determination. Each hen was equipped with a 24-g back-mounted radio transmitter with a harness similar to that described by Dwyer (1972). Radiolocations were obtained on each bird every 3-4 days and daily for nesting birds that were within 3 days of the estimated hatch date. Radio-equipped birds led us to 142 nests, 129 of which furnished sufficient data for calculating nest survival rates.

Because our study area was large, we depended primarily on aircraft for obtaining the initial location of radio-equipped birds (Gilmer et al. 1981). Subsequent visual observations and location of nests were obtained by ground observers using hand-held yagi antennas. To avoid unnecessary disturbance, nests were visited only twice—the first time when the nest was found, the second time when telemetry data indicated termination of the nest.

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