Fred Cooke

Winter philopatry in migratory waterfowl

Philopatry in migratory species can apply to any location used during the annual cycle. The degree of philopatry influences the genetic structure of populations, but only at the stage of the annual cycle when pair formation and gene exchange occur. Because pair formation in birds typically occurs during the breeding season, most studies have fo- cused on breeding-site philopatry. Waterfowl (Anseriformes) are an important exception to this pattern because pair formation often occurs during the winter months. Yet, surprisingly few studies have examined winter philopatry in waterfowl. To serve as an impetus for future research, we summarize published information on winter philopatry in waterfowl and ex- amine these patterns in light of current hypotheses proposed to explain philopatric behavior. Our analyses indicate that geese, swans, and sea ducks show high levels of winter philopatry, with homing rates varying between 49 and 98% to small study areas. In contrast, return rates (0 to 20%) and homing rates (35 to 85%) to large study areas probably are comparatively lower for dabbling ducks and pochards. Unfortunately, detailed comparisons among groups are hindered by variation in the scale at which philopatric behavior is evaluated (ranging from <1 km2 to 105 kM2), and by confounding of return rates with homing rates. Future studies of winter philopatry would benefit by the adoption of a more standardized meth- odology. Many of the hypotheses proposed to explain breeding philopatry apply equally well to winter philopatry. In particular, both genetic and ecological mechanisms may play a role in the evolution of philopatry to the wintering ground. Additional field studies are needed to test these hypotheses, and we suggest future directions for a more detailed ex- amination of this neglected area of research. Received 9 September 1996, accepted 28 April 1998.

Reproductive Habits in the Snow Goose: The Influence of Female Age

Parental age influences reproductive performance in several avian species. Clutch size increases and nesting becomes earlier after the first year of breeding in certain species (e.g., Great Tit (Parus major), Kluijver 1951; Blacklegged Kittiwake (Ra Canada Goose (Bruntu cunudensis muxha), Brakhage 1965). Other species show no effect of female age and, in a few instances, clutch size declines with age (see Klomp 1970). The correlation of parental age with hatching and fledging success shows similar variability among species. In many colonial nesting species, young birds establish territories in peripheral or marginal habitats (e.g. Coulson 1971) either because of their inferior competitive ability in acquisition of central nest sites (Coach 1958, WynneEdwards 1962) or because adults, nesting earlier, establish central territories by precedence ( Coulson 1971). The Lesser Snow Goose ( Anser cuerulescens caerulescens; Delacour 1954) has been under study at a small nesting colony (3,000 pairs) at La P&rouse Bay, Manitoba (58”24’ N 94”24’ W) since 1968. Many of the birds of this colony are individually identifiable through coded plastic leg bands. In this paper, we examine the age of females as a factor affecting the spatial distribution of nests in the colony, reproductive success and the timing of nesting. Annual differences in the proportion of young birds that nest are also examined. Male geese that hatch at La P&rouse Bay seldom return to the colony after reaching reproductive maturity (Cooke et al. 1975). We have, therefore, been unable to establish a population of banded males of known age and to examine the influence of male age on reproduction.

GENE FLOW BETWEEN BREEDING POPULATIONS OF LESSER SNOW GEESE

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

Environmental change and the cost of philopatry: an example in the lesser snow goose

The consequences of philopatric and dispersal behaviours under changing environmental conditions were examined using data from the colony of Lesser Snow Geese (Anser caerulescens caerulescens) breeding at La Pérouse Bay, Manitoba, Canada. In response to increased population size and decreased food abundance over time, increasing numbers of family groups have been dispersing from the traditional feeding areas. Goslings from dispersed broods were significantly heavier (7.3%), and had longer culmens (3.1%), head lengths (2.6%) and marginally longer tarsi (1.9%) on average than goslings that remained within La Pérouse Bay itself. These differences were consistent in each of 5 years. There was no evidence that the larger size of dispersed goslings was due to either a tendency for larger adults to disperse to alternative sites, or increased mortality of smaller goslings among dispersed broods. The most likely cause for the larger size of goslings from dispersed broods was the significantly greater per capita availability of the preferred salt-marsh forage species at non-traditional brood-rearing areas. The larger goslings in non-traditional feeding areas showed significantly higher firstyear survival, suggesting that the use of deteriorating traditional feeding areas may currently be maladaptive in this population.

Rape in the Lesser Snow Goose

Rape attempts were found to be a consistent feature of Lesser Snow Goose biology. In the light of attendant male behaviour in response to a rape attempt on his mate as well as rapist behaviour and chronology of rapes relative to nesting, it is suggested that rape is part of the overall reproductive strategy of the male and therefore, evolutionarily relevant.

Intraspecific nest parasitism and extra-pair copulation in lesser snow geese

Intraspecific nest parasitism and extra-pair fertilization contributed significantly to individual reproductive success in a colony of plumage polymorphic lesser snow geese,Chen caerulescens caerulescens, studied for 14 years in northern Manitoba, Canada. Parasitic females preferred to lay in or adjacent to occupied, defended nests, rather than undefended nests. Nesting females usually rolled eggs that had been laid nearby into their nests. Nest-attendant males typically attacked the intruding females mate, who usually remained at a short distance, thereby drawing the resident male away from the nest. Plumage genetics were used to estimate rates of both nest parasitism and extra-pair fertilization. Nests of homozygous dominant blue morph pairs produced 4·03% homozygous recessive white goslings (N = 4938), which must have been unrelated to both parents, providing information on the rate of nest parasitism. Nests of homozygous recessive white morph pairs produced 2·12% blue goslings (N = 45 777), which must have been unrelated to either one or both parents, providing information on the rate of nest parasitism plus extra-pair fertilization. Using colony-wide estimates of the colour ratio of goslings produced (28·5% blue) and of the blue allele frequency in males (21%), it was calculated that nest parasitism accounted for 5·6% of hatching goslings, and that 2·4% of goslings were fathered by extra-pair fertilization.

Assortative mating in lesser snow geese (Anser caerulescens).

Assortative mating occurs in the dimorphic lesser snow geese in the wild. Mixed matings between the blue and white phases are much less frequent than would be expected by chance. Evidence from marked birds in field conditions indicated that mate choice was correlated with familial color. Birds from white families usually chose white mates, birds from blue families usually chose blue mates, and birds from mixed families chose mates of either color. Similar results were obtained under captive conditions when offspring from foster families with particular parental and offspring color combinations were allowed to choose mates. Both parental color and sibling color appeared to influence mate choice. The birds own color did not appear to be important in mate choice in either field or experimental conditions, and in those cases where male and female parents differed in color neither parental color was more influential than the other in determining offspring mate choice. The results provide the first evidence, to our knowledge, that mate selection based on familial appearance operates intraspecifically in the wild.

Sexual selection and spring arrival times of red-necked and Wilson's phalaropes

SummarySeasonal changes in sex ratios during a 4-year study of red-necked phalaropes and a 3-year study of Wilsons phalaropes showed that females preceded males to breeding and/or courtship areas. The degree to which females preceded males may have been constrained by harsh weather, as the arrival of red-necked phalaropes was synchronous in 1983, when spring was unusually late. Neither sex defended territories; females competed vigorously for direct access to males. These findings show that selection for sexually asynchronous arrival need not act through territoriality. We interpret early female arrival as an adaptation for obtaining mates and coclude that sexual selection may be an important determinant of arrival times in mate defense social systems.

Pre-incubation feeding activities and energy budgets of Snow Geese: can food on the breeding grounds influence fecundity?

The potential contribution of early spring feeding conditions in the Arctic to clutch size variation was examined in a population of Lesser Snow Geese Anser caerulescens caerulescens. Behavioural observations were combined with energetic analyses of food material to derive an estimate of the energy budgets of pre-laying and laying females. Food intake of females between arrival on the breeding grounds and incubation was considerable; estimated energy gains in this period were in the same magnitude as the cost of one or several eggs. The pre-laying period spent on the breeding grounds can thus be energetically beneficial rather than costly. Accumulation of resources for reproduction in Snow Geese is a continual process including the breeding grounds, and nutrient limitation after arrival in the Arctic cannot sufficiently explain the environmental component of clutch size variation. The timing of migration and follicle development is such that clutch size decisions are sometimes made during the late stages of migration and some-times after arrival. In the latter case food conditions on the breeding grounds may greatly influence clutch size; in the former case they may still influence readjustments of clutch size after the initial decision. The universal negative correlation between clutch size and laying date in Snow Geese can be explained by negative fitness consequences of late hatching, which outweigh the benefits of delayed laying and further nutrient accumulation. Food shortage on the breeding grounds may sometimes be a secondary factor contributing to seasonal clutch size decline.

Bi-parental care in willow ptarmigan: a luxury?

Abstract Willow ptarmigan, Lagopus lagopus , usually pair monogamously and both parents invest considerable time and energy in the care of offspring. However, the species is occasionally polygynous (5–9%), and in these cases only the females care for offspring. To examine the consequences of uni-parental care for the production of offspring and the body condition of mates, either the male or the female parent was removed at the onset of incubation and at hatch. Natural removals were also observed. Lone hen willow ptarmigan (widows) defended eggs and incubated clutches successfully, whereas single parent males (widowers) did not. After hatch, widows (mates removed either at the onset of incubation or at hatch) and pairs raised equivalent numbers of chicks to fleging, but widowers (mate removed at hatch) were less successful. There were no differences between parental types in numbers of offspring returning in a subsequent season or in the mating status of offspring in the first year of return. Widows and paired hens had similar rates of survival during the breeding season, and, in subsequent years, similar return rates and mate fidelity. Willow ptarmigan, after the onset of incubation, provided more parental care than is required to produce offspring and maintain survival and body condition of their mates. Thus, these hypotheses can be eliminated as probable factors maintaining monogamy for willow ptarmigan at this site during 1981–1984. Bi-parental care in willow ptarmigan may have developed as a salvage strategy for males as a consequence of their remaining throughout incubation to guard their mates and capitalize on the potential to re-nest.