La Perouse Bay Research Articles

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

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.

Recruitment and the Timing of Reproduction in Lesser Snow Geese (Chen caerulescens caerulescens)

Abstract Recruitment of offspring into a breeding population of Lesser Snow Geese (Chen caerulescens caerulescens) at La Perouse Bay, Manitoba was used as a measure of reproductive success to assess the relative fitness of females who hatched their clutches early, middle, and late in the breeding season. In three of seven seasons investigated, goslings from early-hatching clutches showed significantly greater recruitment rates than their middle- or late-hatching counterparts. No significant differences in recruitment rates were detected in the other four seasons, although early-hatching clutches showed numerically higher recruitment rates in three of these seasons. There is, therefore, some indication of directional selection for early breeding. This conclusion contrasts with that drawn by Cooke and Findlay (1982), who, using fledging success as a measure of reproductive fitness, showed that females whose clutches hatched in the middle period had the highest fitness and concluded that the population was being exposed to stabilizing selection for synchronization. The discrepancy between these results and those presented in this paper indicates that conclusions concerning the action of selection in natural populations depend heavily upon the stage of the life cycle during which reproductive success is estimated. As such, evolutionary biologists must be cautious of relying too heavily on measures taken too early in the life of the organism.

Life history studies of the Lesser Snow Goose (Anser caerulescens caerulescens)

We examined the spatial distribution of nesting cohorts of female Lesser Snow Geese (Anser caerulescens caerulescens) in a small colony located at La Perouse Bay, Manitoba. In general, cohorts show a heterogeneous spatial distribution, which arises from a tendency of females of the same cohort affiliation to cluster together. Further-more these associations are maintained through time, such that cohorts tend to dominate particular regions of the colony over several breeding seasons. These findings provide further evidence for breeding site fidelity among female lesser snow geese.

A Genetic Analysis of Lesser Snow Goose Families

ALTHOUGH genetic polymorphism is well-documented with respect to avian plumage color, surprisingly few studies have investigated the genetic basis of the polymorphism. The major limitations on studies of this nature have been an inadequate sample size and a lack of expression of the polymorphic character at some stage in the life cycle. In the Lesser Snow Goose, Anser caerulescens caerulescens, these limitations do not apply and it has been possible to undertake an investigation into the blue and white phases of this species. Earlier work has indicated that the dimorphism is regulated by a single pair of alleles with the blue phase dominant over white (Cooke and Cooch, 1968). This conclusion was based on analyses where data from several different families were pooled to give genetic ratios. This method, while adequate to show the probable genetic basis for the polymorphism, would have been more convincing if individual families had been available for analysis. Further, it gave no clear indication as to whether the gene controlling color was sex-linked or not. During the summers of 1968, 1969, and 1970 it was possible to collect individual family data from the La Perouse Bay colony near Churchill, Manitoba. An analysis of data from families collected from this colony has supported the earlier findings of Cooke and Cooch as well as demonstrating that the gene is autosomal and not sex linked. METHODS Collection of data.-In the breeding colony, nests were marked with stakes and numbered several days prior to hatch. Much of the colony was marked in this manner, and it is thought that no sampling bias exists. At hatch both parents remain near the nest, and at this time the phenotypes of parents and goslings could be scored. The color phases were recorded according to the criteria of Cooke and Cooch (1968), and little difficulty was encountered in assigning birds a given color category. Families were recorded only at the marked nest site. If all goslings had not hatched when a given nest was visited, the family was recorded as having only those offspring that had hatched, even though the final family size would presumably be larger. This could give the data some bias if certain genotypes hatch earlier than others. Families with more than five offspring were ignored in the statistical analysis, as it has been shown (Cooch, 1961), and the present study confirms,that large families have a tendency to arise from two or more females laying eggs in the same nest. Segregation analysis.-A number of features of the Lesser Snow Goose restricted the type of genetic analysis that could be attempted on the sample population.

AGE OF LAVA FLOWS ON HALEAKALA, MAUI, HAWAII

La Perouse9s chart of the Hawaiian Islands, drawn in 1786, was compared with Vancouver9s chart of 1793 in an attempt to date the lava flow near La Perouse Bay, Maui. The prominent bulge formed by the flow is shown by Vancouver but not the accurately drawn chart of La Perouse, so that the date of eruption of the flow may be set at 1790 ± 4 years.