SPACING BEHAVIOR AND REPRODUCTIVE ECOLOGY OF THE SEMIPALMATED PLOVER AT CHURCHILL, MANITOBA

We documented solitary and aggregative spacing patterns in Semipalmate d Plovers (Charadrius semipalmatus) near Churchill, Manitoba. Pairs ne sting on gravel directly on the coast nested in larger aggregations an d closer to other pairs than inland pairs. Coastal areas were similar to inland areas in (1) density of birds, (2) available gravel nesting habitat, and (3) climatic conditions. The number of pairs per gravel a rea deviated significantly from that expected from a Poisson distribut ion. Inland nests were significantly uniform in distribution, whereas coastal nests were distributed randomly among four sites. In 1988, pai rs nesting on the coast also nested later and had heavier eggs and chi cks than pairs nesting inland. Reproductive success in two years of st udy was higher at coastal nests than at inland nests. We suggest that the differences in spacing between the two sites may be due to differe nt predator populations at the two sites.