The vegetation at a Lesser Snow Goose breeding colony was examined to determine if particular plant species or species associations were characteristic of the nest sites of the geese. A stepwise discriminant analysis revealed that nest sites could be satisfactorily distinguished from the ambient vegetation using 2 of the 29 plant species growing in the quadrats. These two species, lyme grass (Elymus arenarius ssp. mollis) and arctic daisy (Chrysanthemum arcticum ssp. polare) were strongly associated with Snow Goose nest sites.Possible explanations for the association are examined. It is suggested that rather than a cause and effect relationship between plants and nest sites, E. arenarius and C. arcticum have similar ecological requirements to those of the geese for a nesting site.
THE measurement of gene flow between natural populations of animals in the field has rarely been achieved in population biology.The nesting colonies of Lesser Snow Geese (Chen c. caerulescens) in the Hudson Bay area provide a favorable situation for such measurements-they are relatively discrete, often separated by hundreds of miles (Fig. 1), and, at many of the colonies, large numbers of geese have been marked with leg bands, facilitating the detection of movement between colonies.The Lesser Snow Goose is dichromatic, comprising blue and white (snow) phases; this dichromatism is controlled by a single gene or tightly linked group of genes (Cooke and Mirsky 1972).In this paper the names Lesser Snow Goose or Snow Goose will be used to denote the species, and blue and white to denote the color phases.The ratios of blue to white phase individuals differ significantly from colony to colony and have changed within colonies in the recent past (Cooch 1963).A westward spread of the blue phase led Cooch to postulate some exchange between colonies.The lack of morphological differentiation between Lesser Snow Geese from different colonies (in contrast to that of Canada Geese (Branta canadensis) nesting in the same region that show significant regional morphological variation (Maclnnes 1966)) is consistent with the considerable gene exchange between different Snow Goose colonies.The two color phases mate assortatively (Cooch and Beardmore 1959).Cooke and Cooch (1968), on the basis of a genetic analysis of the Boas River colony, postulated that individuals select mates according to the color phase of their parents.Mate selection might be modified by the relative availability of each color phase at the time of mate selection.Lemieux and Heyland (1967) and Cooch (1961) showed that white phase birds from the Koukdjuak and Boas River colonies, respectively, tended to have a more westerly fall migration route and wintering range than blue phase birds from the same colonies, although separation was far from absolute.This phenomenon is hereafter referred to as differential phase migration.The migration and wintering distributions of the two colonies shared large areas of overlap, indicating that birds from at least two colonies mixed at this time.If pair formation occurred during this period, interchange between colonies would result unless the geese possessed a special means of recognizing birds from their own colony or unless birds from a single colony maintained exclusive flocks.The purpose of this paper is to determine the amount of gene flow
The interplay between gene flow and selection is examined in the chromatic lesser snow goose (Anser caerulescens caerulescens). A major component of this species nests in several large colonies (segments) in the Canadian Arctic and migrates to the gulf coast of Texas and Louisiana, where there is considerable mixing of birds from different segments. Pair formation occurs when birds from different nesting segments are mixing and frequently occurs between birds from different segments. Females usually return to their natal nesting segment, whereas males only do so if they pair with birds from their own natal segment. The consequence is considerable gene flow among the different nesting segments. Gene flow into the small nesting segment at La Pérouse Bay, Manitoba, is estimated to be around 50% per generation. Gene flow into the larger segments is expected to be somewhat less. With this amount of gene flow, one would expect little local adaptation within the various nesting segments. This conclusion is examined in view of the apparently stable differences in color frequencies among the nesting segments. It is argued that behavioral aspects of the breeding biology of the species, rather than natural selection, sufficiently account for both the massive gene flow and the color differentiation among nesting segments.
This book augments discussions of behavioural ecology with a comprehensive study of a single species, using it to illustrate and discuss many theoretical issues. Taking the shelduck as its principal example, the book considers how an animal's behaviour helps it to survive and reproduce in a hostile environment. It also discusses the effects of behaviour, particularly social behaviour, in the limitation of animal population size. The arrangement of the text follows the phases of the shelduck's annual cycle and discusses the different behavioural problems encountered at each stage. In this account a wide variety of topics in behavioural ecology have been brought together and applied to a thorough field study of this highly territorial species.
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.
The reproductive performance of Lesser Snow Geese (Anser caerulescens caerulescens) at La Pérouse Bay was examined in individuals retaining and in those changing their mate of the previous breeding season. Females retaining their mate had on average a slightly higher clutch size than those which did not. Other measures of reproductive success did not differ significantly between the two groups. The phenomenon of larger clutch size was not detectable in samples of older females. Females breeding for the second time, whether they changed mates or not, had a smaller clutch than did older birds, and clutch size was found to increase with age and/or experience, at least up to the third breeding attempt. We conclude that there is no causative relationship between mate loss and lowered clutch size. Nevertheless, females who breed for the first time are more likely to lose their mates and to have a lower-than-average clutch size as second-time breeders. In addition, first-time breeders were less co-ordinated in nest defense than more experienced birds.
