Philopatry, Site Tenacity, and Mate Fidelity in the Semipalmated Sandpiper

Abstract

Philopatry, site tenacity, and mate fidelity were examined in a 5-yr study of a population of male-territorial, monogamous Semipalmated Sandpipers (Calidris pusilla) breed- ing at La Perouse Bay, near Churchill, Manitoba. There was no sex bias in natal philopatry and no significant difference in adult philopatry, although males tended to return to the breeding area at higher frequencies than females. However, males nested significantly closer to previous nests than did females. Pairs that had reunited did not move as far from their previous nest site as birds that had changed mates, and this effect was more pronounced in females. Birds that had nested successfully the previous year returned at higher rates than those that had been unsuccessful. However, there was no significant difference in distance moved from a previously successful vs. unsuccessful nest. There also was no significant difference in site tenacity when distances one and two years or two and three years apart were compared. However, nest distances increased significantly when three years had elapsed between utilization of sites. Each year approximately 50% of the marked birds in the study area had reunited with their mate of the previous year. If both members of the pair returned, close to 80% remained paired. There was no tendency for birds that had divorced to have been less successful nesters in the previous year, compared to pairs that had reunited. Subsequent nesting success was not significantly different between birds that had changed or retained mates. However, in 1 of 4 yr, nests of pairs that had changed mates hatched significantly later than did those of remated pairs. Received 23 April 1984, accepted 4 October 1984. IN recent years a number of authors have dis- cussed the influence of social structure and mating system on philopatry and dispersal. Gauthreaux (1978) proposed that dominance hierarchies in a population could explain dif- ferential dispersal and migration between the sexes, as well as among age groups. Greenwood (1980), however, refuted Gauthreaux's hypoth- esis with respect to differential sex dispersal. Greenwood noted that while males are domi- nant to females in most mammals, mammals rarely show female-biased dispersal. He sug- gested that the direction of the sex bias in dis- persal could be predicted from the mating sys- tem. In a resource-defense (territorial) system, the sex that defends the resource would be ex- pected to be more philopatric. This assumes that acquisition and/or maintenance of a breeding territory, for example, would be facilitated by familiarity with the area. Dispersal of one sex relative to the other is thought to be related to the level of genetic similarity between poten- tial mates insofar as no dispersal may present a loss in breeding success due to inbreeding, but too much dispersal may lead to genetic in- compatibility (Shields 1983). Factors other than gender also may have an effect on adult philopatry and site tenacity. These include mate change (Wilcox 1959), pre- vious breeding success (Oring and Lank 1982, Oring et al. 1983), and number of years elapsed between nest sites.