James S. Sedinger

Environmental Influence on Life-History Traits: Growth, Survival, and Fecundity in Black Brant (Branta Bernicla)

We studied relationships between body size of female Black Brant goslings (Branta bernicla nigricans) late in their growth period and first year survival, eventual adult body size, breeding propensity, and size and volume of clutches they eventually produced to examine the relationship between growth and fitness in this population. We indexed body size by calculating PC1 scores based on either culmen and tarsus, or culmen, tarsus, and mass. Gosling (PC scores based on culmen and tarsus) size was positively correlated with resighting rate (P = 0.005), indicating that larger goslings survived at a higher rate than did smaller goslings. Gosling size was correlated with adult size of the same individuals (P = 0.0004). Larger goslings were more likely to breed as 2- or 3-yr-olds than were medium or small goslings (P = 0.008). Larger adult brant laid more eggs (P = 0.03) and produced clutches with greater total volume (P = 0.03) than did smaller brant. Given the important role of foraging environment in growth of goslings, these data suggest an important role of early environment in determining life-history traits.

Timing of nesting by Canada geese in relation to the phenology and availability of their food plants

(1) This study examined seasonal variation in the foraging behaviour of cackling Canada geese (Branta canadensis minima) and in the nutrient content and availability of tundra grasses and sedges (graminoids) and arrowgrass during the nesting and brood-rearing periods, 1977-79 on the Yukon-Kuskokwim Delta, Alaska. (2) Nitrogen concentrations in nearly all graminoids and arrowgrass began to decline either prior to, or during, hatching of cackling goose clutches. Grazing or clipping of vegetation resulted in higher and prolonged peaks in nitrogen concentration but peak nitrogen levels in these plants still occurred within a week of the end of the hatching period. (3) Standing crops of graminoids increased until early August while the standing crop of arrowgrass (the most nutritious plant in the diet) in preferred foraging habitat began to decline in mid-July due to grazing by geese. (4) Peck-rates of adult cackling geese tended to decline as brood-rearing progressed, indicating that preferred foods declined in availability during this period. Also, late in brood-rearing, preferred foraging areas were used less and arrowgrass comprised a smaller proportion of the diet. (5) Changes in plant nutrient levels and shifts in diet and habitat use reduced the nutritional quality of the diet as brood-rearing progressed. Thus, as a result of both the natural phenology of tundra plants and grazing by geese, late hatching broods were at a nutritional disadvantage compared to those hatching early. (6) We conclude that a seasonal decline in the quality of foraging conditions is probably an important factor favouring early nesting by geese.

Feedback dynamics of grazing lawns: coupling vegetation change with animal growth

We studied the effects of grazing by Black Brant (Branta bernicla nigricans) geese (hereafter Brant) on plant community zonation and gosling growth between 1987 and 2000 at a nesting colony in southwestern Alaska. The preferred forage of Brant, Carex subspathacea, is only found as a grazing lawn. An alternate forage species, C. ramenskii, exists primarily as meadow but also forms grazing lawns when heavily grazed. We mowed plots of ungrazed C. ramenskii meadows to create swards that Brant could select and maintain as grazing lawns. Fecal counts were higher on mowed plots than on control plots in the year after plots were mowed. Both nutritional quality and aboveground biomass of C. ramenskii in mowed plots were similar to that of C. subspathacea grazing lawns. The areal extent of grazing lawns depends in part on the population size of Brant. High Brant populations can increase the areal extent of grazing lawns, which favors the growth of goslings. Grazing lawns increased from 3% to 8% of surface area as the areal extent of C. ramenskii meadows declined between 1991 and 1999. Gosling mass was lower early in this time period due to density dependent effects. As the goose population stabilized, and area of grazing lawns increased, gosling mass increased between 1993 and 1999. Because larger goslings have increased survival, higher probability of breeding, and higher fecundity, herbivore-mediated changes in the distribution grazing lawn extent may result in a numerical increase of the population within the next two decades.

NATAL AND BREEDING PHILOPATRY IN A BLACK BRANT, BRANTA BERNICLA NIGRICANS, METAPOPULATION

We estimated natal and breeding philopatry and dispersal probabilities for a metapopulation of Black Brant (Branta bernicla nigricans) based on observations of marked birds at six breeding colonies in Alaska, 1986–1994. Both adult females and males exhibited high (>0.90) probability of philopatry to breeding colonies. Probability of natal philopatry was significantly higher for females than males. Natal dispersal of males was recorded between every pair of colonies, whereas natal dispersal of females was observed between only half of the colony pairs. We suggest that female-biased philopatry was the result of timing of pair formation and characteristics of the mating system of brant, rather than factors related to inbreeding avoidance or optimal discrepancy. Probability of natal philopatry of females increased with age but declined with year of banding. Age-related increase in natal philopatry was positively related to higher breeding probability of older females. Declines in natal philopatry with year of banding corresponded negatively to a period of increasing population density; therefore, local population density may influence the probability of nonbreeding and gene flow among colonies.

Adaptations to and consequences of an herbivorous diet in grouse and waterfowl

I review diet selection in grouse and waterfowl in the context of their herbivorous diets and discuss adaptations to herbivory in these groups. Both grouse and waterfowl prefer plant foods containing higher concentrations of protein than nonpreferred foods; grouse and small waterfowl include invertebrates in the diet to meet protein demands during periods of high tissue production. Grouse tend to avoid plant foods containing high concentrations of anti-herbivore compounds and the relative roles of these compounds versus nutrients in diet selection by grouse is presently unclear. Grouse and waterfowl have similar digestive morphology, except for the ceca, which are 5 times longer in grouse than in geese. Enlarged ceca are associated with improved nitrogen economy in grouse; evolution of these structures in geese may have been precluded by energetic costs of carrying enlarged ceca during migration.

Estimating prefledging survival: allowing for brood mixing and dependence among brood mates

Estimates of juvenile survival from hatch to fledging provide important information on waterfowl productivity. We develop a model for estimating survival of young waterfowl from hatch to fledging. Our model enables interchange of individuals among broods and relaxes the assumption that individuals within broods have independent survival probabilities. The model requires repeated observations of individually identifiable adults and their offspring that are not individually identifiable. A modified Kaplan-Meier procedure (Pollock et al. 1989a,b) and a modified Mayfield procedure (Mayfield 1961, 1975; Johnson 1979) can be used under this general modeling framework, and survival rates and corresponding variances of the point estimators can be determined.

Seasonal and annual survival of adult Pacific brant

Declining mid-winter counts of Pacific brant (Branta bernicla nigricans) and reduced numbers of nesting birds on their main breeding grounds prompted us to assess factors that may be limiting recovery of this population. We estimated seasonal and annual survival rates of adult brant in 1986-93 from resightings of leg-banded birds. Brant were banded at a major colony on the Yukon-Kuskokwim Delta, Alaska (Y-K Delta) in 1986-92, and resighted there in 1987-93 as well as at major fall and spring migration and wintering areas in 1990-93. Seasonal survival was the same for males and females. Mean monthly survival rate was lowest (P ≤ 0.05) in late spring migration (15 Apr-1 Jun), the period of greatest subsistence harvest on the breeding grounds, and highest in winter (1 Jan-1 Mar), the period of greatest sport harvest. Annual survival rate did not vary among years (F = 0.51; 5, 718 df; P = 0.91) and averaged 0.840 (SE = 0.031) from 1986 to 1993. Subsistence harvest has contributed to low population levels of Pacific brant.

Reproductive implications of egg-size variation in the black brant

-We analyzed variation in egg size of Black Brant (Branta bernicla nigricans) in relation to clutch size, laying date, female age, year, and position in the laying sequence. A total of 3,478 eggs was measured over three years. Egg size increased with clutch size and female age, and decreased with laying date, year, and position in the laying sequence. We did not detect a negative phenotypic correlation between clutch size and egg size. However, overlap in total clutch volumes for clutches of different sizes indicated trade offs occurred among individuals with comparable investments in their clutches. Received 1 October 1991, accepted 30 March 1992. THE COMBINATION of clutch size and egg size determines the total energetic investment in clutch formation by a laying female. Egg size may affect female fitness through its effects on initial size, early growth and survivorship of hatchlings (Cole 1979, Ankney 1980, Thomas and Brown 1988, Sedinger and Flint 1991), whereas clutch size is related to fitness via its effect on the potential number of offspring produced (Lessells 1986). Arctic-nesting geese rely heavily on stored lipid and protein reserves for egg production and incubation (Ankney and MacInnes 1978, Raveling 1979, Ankney 1984). Thus, nutrients available for a clutch are limited and at least partially predetermined when geese arrive on the breeding grounds. This limitation on reproductive investment, combined with the fitness advantages of both large clutches and large eggs, creates the potential for both ultimate and proximate trade offs between clutch size and

Foraging behavior of cackling Canada Goose goslings: implications for the roles of food availability and processing rate

SummaryTime spent foraging (and in other activities), rate of pecking at food items and length of foraging and nonforaging periods were studied in cackling Canada goose (Branta canadensis minima) goslings during brood-rearing on the Yukon-Kuskokwim Delta, Alaska in 1978 and 1979. Brood density on the study area was twice as high in 1978 (23 broods) as in 1979 (12 broods) owing in part to annual variation in nesting density and success. Peck-rates were lower in meadows during 1978 than in 1979. There was no between-year difference in time spent foraging prior to the adult molt (59% of daylight hours) but during molt, goslings spent more time feeding in 1978 (70%) than in 1979 (56%). Prior to the adult molt, 12.2 and 11.9 hours were spent feeding each day in 1978 and 1979 respectively, whereas goslings fed for 13.4 and 10.6 hours daily, in the two years during molting and fledging. Increased foraging time during the molt in 1978 completely compensated for lower peck rates so that total number of pecks per day during this period were similar in 1978 (62,800 pecks/d) and 1979 (57,900 pecks/d). Elsewhere, we reported that cackling geese significantly reduced the availability of their preferred food in 1979 and this food comprised a smaller proportion of the diet in 1978 than 1979. This variation in diet suggests that preferred foods were less available at higher brood densities, resulting in annual variation in foraging behavior. Lengths of foraging periods increased during brood-rearing in both years but were longer on average in 1978. There was no seasonal or between year variation in the length of nonforaging periods. The alternating pattern of foraging and nonforaging periods suggests that rate of processing limits rate of food intake because a relatively constant period of time was regularly required to empty the esophagus before foraging could be resumed. The restriction of food intake by digestive processes increased the importance of dietary nutrient concentrations because low nutrient concentrations could not be compensated for by higher rates of food intake.

Archiving primary data: solutions for long-term studies

The recent trend for journals to require open access to primary data included in publications has been embraced by many biologists, but has caused apprehension amongst researchers engaged in long-term ecological and evolutionary studies. A worldwide survey of 73 principal investigators (Pls) with long-term studies revealed positive attitudes towards sharing data with the agreement or involvement of the PI, and 93% of PIs have historically shared data. Only 8% were in favor of uncontrolled, open access to primary data while 63% expressed serious concern. We present here their viewpoint on an issue that can have non-trivial scientific consequences. We discuss potential costs of public data archiving and provide possible solutions to meet the needs of journals and researchers.