Population Studies of the Polyandrous Spotted Sandpiper

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Abstract
A color-banded population of Spotted Sandpipers (Actitis macularia) was studied over a 10-yr period on Little Pelican Island, Leech Lake, Minnesota. A total of 75 females and 107 males bred for 144 ♀ ♀ yr and 200 ♂ ♂ yr. The observed skew in the population sex ratio was due primarily to behavioral exclusion of inexperienced females. Density appeared to limit population size and productivity. Locally hatched chicks accounted for 31% and 40% of the breeding females in the final 2 yr. Females laid eggs for 1.35-2.06 males per year. Experienced females had significantly more mates, eggs, chicks, and fledglings than did inexperienced females. Locally hatched chicks accounted for 21% and 19% of the breeding males in the final 2 yr. Males mated with 1.0-1.4 females per year. Experienced males had more mates and received more replacement eggs than did inexperienced males; in contrast to females, however, inexperienced males had no less hatching or fledging success than did experienced males. Thirty-eight marked females and 16 marked males tried unsuccessfully to enter the population, and 6 females and no males were observed to be nonbreeders all season long. Of 1,142 eggs, 442 hatched and 256 fledged. Experienced birds returned to breed more often in subsequent years than did inexperienced ones (61% vs. 50%). Return rates of successful birds were consistently higher than those of unsuccessful birds, the difference decreasing with age. Young males appeared to be less site-faithful than were females and older males. Successfully breeding females lived an average of 3.7 yr. Relative to other scolopacids with multipurpose territories, the Spotted Sandpiper is considered a pioneering species that quickly and frequently colonizes new sites, emigrates in response to reproductive failure, breeds first at an early age, lives a relatively short time, lays many eggs per female per year, and has relatively low nest success.

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