Joel A. Schmutz

Winter survival of adult female harlequin ducks in relation to history of contamination by the Exxon Valdez oil spill

Harlequin duck (Histrionicus histrionicus) life-history characteristics make their populations particularly vulnerable to perturbations during nonbreeding periods. The 1989 Exxon Valdez oil spill was a major perturbation to nonbreeding habitats of harlequin ducks in Prince William Sound, Alaska, which resulted in population injury. To assess the status of population recovery from the oil spill and to evaluate factors potentially constraining full recovery, we used radiotelemetry to examine survival of adult female harlequin ducks during winters of 1995-96, 1996-97, and 1997-98. We implanted 294 harlequin ducks (154 and 140 in oiled and unoiled areas, respectively) with transmitters and tracked their signals from aircraft during October through March. We examined variation in survival rates relative to area and season (early, mid, and late winter) through comparisons of models using Akaikes information criterion (AIC c ) values. The 3 models best supported by the data indicated that survival of birds in oiled areas was lower than in unoiled areas. Inclusion of standardized body mass during wing molt in the 3 best models did not improve their fit, indicating that body mass during wing molt did not affect subsequent winter survival. In the model that best fit our data, survival was high in early winter for both areas, lower during mid and late winter seasons, and lowest in oiled areas during mid winter. Cumulative winter survival estimated from this model was 78.0% (SE = 3.3%) in oiled areas and 83.7% (SE = 2.9%) in unoiled areas. We determined that area differences in survival were more likely related to oiling history than intrinsic geographic differences. Based on a demographic model, area differences in survival offer a likely mechanism for observed declines in populations on oiled areas. Concurrent studies indicated that harlequin ducks continued to be exposed to residual Exxon Valdez oil as much as 9 years after the spill. We suggest that oil exposure, mortality, and population dynamics were linked and conclude that continued effects of the oil spill likely restricted recovery of harlequin duck populations through at least 1998.

Determinants of reproductive costs in the long-lived Black-legged Kittiwake: A multiyear experiment

We studied reproductive costs of Black-legged Kittiwakes (Rissa tridactyla) in Prince William Sound, Alaska (USA) by removing entire clutches from randomly selected nests over four successive years, and then contrasting survival and fecundity of adults from manipulated and unmanipulated nests in each subsequent year. To elucidate mechanisms that lead to the expression of reproductive costs, we simultaneously characterized several behavioral and physiological parameters among adults in the two treatment groups. We also examined naturally nonbreeding adults that previously bred to determine their survival and future nonbreeding probabilities. Food availability varied during the study, being generally poor at the onset, and improving in later years. Adult nest attendance and body condition (assessed late in the chick- rearing period) varied accordingly among years, and between adults raising chicks and adults that had their eggs removed. Adults from unmanipulated nests incurred significant survival costs in all years, although fecundity costs were strongly expressed in only one of four years. Neither survival nor fecundity costs were strongly influenced by body condition or food availability, and no difference in reproductive costs was detected between the sexes. Although unmanipulated breeders survived at lower rates than manipulated breeders due to costs of reproduction, their survival rates were elevated compared to those of natural nonbreeders, presumably due to differences in individual ability. These findings indicate that models of adult survival must consider not only an organisms reproductive state, but also the factors that lead to that state. Although body condition appeared to be weakly related to survival, it was insufficient to explain the full magnitude of survival costs observed. We suggest that other parameters that were found to differ between treatment groups (e.g., rates of energy turnover, baseline levels of stress, and patterns of allocating body reserves) may be important mechanistic determinants of reproductive costs in kittiwakes, and potentially other long-lived species. Future efforts should move beyond simple assessments of body condition and toward more integrated measures of physiological condition when attempting to identify factors that influence how long-lived species balance the costs and benefits of reproduction.

Relative effects of survival and reproduction on the population dynamics of emperor geese

Populations of emperor geese (Chen canagica) in Alaska declined sometime between the mid1960s and the mid-1980s and have increased little since. To promote recovery of this species to former levels, managers need to know how much their perturbations of survival and/or reproduction would affect population growth rate (X). We constructed an individual-based population model to evaluate the relative effect of altering mean values of various survival and reproductive parameters on X and fall age structure (AS, defined as the proportion of juv), assuming additive rather than compensatory relations among parameters. Altering survival of adults had markedly greater relative effects on A than did equally proportionate changes in either juvenile survival or reproductive parameters. We found the opposite pattern for relative effects on AS. Due to concerns about bias in the initial parameter estimates used in our model, we used 5 additional sets of parameter estimates with this model structure. We found that estimates of survival based on aerial survey data gathered each fall resulted in models that corresponded more closely to independent estimates of A than did models that used mark-recapture estimates of survival. This disparity suggests that mark-recapture estimates of survival are biased low. To further explore how parameter estimates affected estimates of X, we used values of survival and reproduction found in other goose species, and we examined the effect of an hypothesized correlation between an individuals clutch size and the subsequent survival of her young. The rank order of parameters in their relative effects on A was consistent for all 6 parameter sets we examined. The observed variation in relative effects on A among the 6 parameter sets is indicative of how relative effects on A may vary among goose populations. With this knowledge of the relative effects of survival and reproductive parameters on A, managers can make more informed decisions about which parameters to influence through management or to target for future study. J. WILDL. MANAGE. 61(1):191-201

Prey density and the behavioral flexibility of a marine predator: The common murre ( Uria aalge )

Flexible time budgets allow individual animals to buffer the effects of variable food availability by allocating more time to foraging when food density decreases. This trait should be especially important for marine predators that forage on patchy and ephemeral food resources. We examined flexible time allocation by a long-lived marine predator, the Common Murre (Uria aalge), using data collected in a five-year study at three colonies in Alaska (USA) with contrasting environmental conditions. Annual hydroacoustic surveys revealed an order-of-magnitude variation in food density among the 15 colony-years of study. We used data on parental time budgets and local prey density to test predictions from two hypotheses: Hypothesis A, the colony attendance of seabirds varies nonlinearly with food density; and Hypothesis B, flexible time allocation of parent murres buffers chicks against variable food availability. Hypothesis A was supported; colony attendance by murres was positively correlated with food over a limited range of poor-to-moderate food densities, but independent of food over a broader range of higher densities. This is the first empirical evidence for a nonlinear response of a marine predators time budget to changes in prey density. Predictions from Hypothesis B were largely supported: (1) chick-feeding rates were fairly constant over a wide range of densities and only dropped below 3.5 meals per day at the low end of prey density, and (2) there was a nonlinear relationship between chick-feeding rates and time spent at the colony, with chick-feeding rates only declining after time at the colony by the nonbrooding parent was reduced to a minimum. The ability of parents to adjust their foraging time by more than 2 h/d explains why they were able to maintain chick-feeding rates of more than 3.5 meals/d across a 10-fold range in local food density.

Survival and pre-fledging body mass in juvenile emperor geese

Wood Duck: a review, p. 45-60. In L. H. Fredrickson, G. V. Burger, S. P. Havera, D. A. Graber, R. E. Kirby, and T. S. Taylor [eds.], Proc. 1988 North Am. Wood Duck Symp., St. Louis, MO. HEPP, G. R., R. A. KENNAMER, AND W. F. HARVEY, IV. 1989. Recruitment and natal philopatry of Wood Ducks. Ecology 70:897-903. HEPP, G. R., R. A. KENNAMER, AND W. F. HARVEY, IV. 1990. Incubation as a reproductive cost in female Wood Ducks. Auk 107:756-764. KENNAMER, R. A., AND G. R. HEPP. 1987. Frequency and timing of second broods in Wood Ducks. Wilson Bull. 99:655-662. LEOPOLD, F. 1951. A study of nesting Wood Ducks in Iowa. Condor 53:209-220. LIMA, S. L. 1987. Clutch size in birds: a predation perspective. Ecology 64:1062-1070. MARTIN, K., AND F. COOKE. 1987. Biparental care in Willow Ptarmigan: a luxury? Anim. Behav. 35: 369-379.

Effects of neck collars and radiotransmitters on survival and reproduction of emperor geese

Neck collars have been used widely for studies of goose population biology. Despite concerus abon their negative impacts, few studies have employed designs capable of clearly demonstraling these effects. During a 1993-98 study of emperor geese (Cheu canagica), we contrasted survival and reproduction of gees clarked with tarsal bands to those marked with either small neck collars, large neck collars, or small neck collars with attached radiotransmitters. Ammal survival of adult females marked with tarsal bands varied among years and averaged 0.807 ± 0.140 (x ± SE. Survival of geese with other types of markers also varied among years but was lower (0.610 ± 0.198). Collars with radiotransmitters lowered breeding propensity, as indexed by resighting rates. Although elutch sizes of tarsal banded birds were similar to those for unmarked birds, other markers reduced elutch sizes by about 1 egg. Egg mass and hatch date were not affected by marker type Future studies of goose demographics should scriously consider use of alternative markers.

Survival of greater white-fronted geese: Effects of year, season, sex, and body condition

Information regarding the magnitude and variation in survival rates is necessary for understanding the causes of large changes in population size. We examined survival of greater white-fronted geese (Anser albifrons frontalis) in the Pacific Flyway during 1979-82. The population declined by 75% in the decade preceding our study but was stable during our investigation. Annual survival of adults (0.749, SE = 0.045) was 7% higher than during an earlier study. We developed a simple population model which suggests that recent (1985-96) survival rates may be as much as 10% higher in adults than the 1979-82 rate, which corresponds to population increases observed since 1985. Survival of adult females varied seasonally; monthly survival during a period of winter when no hunting or migration occurred was higher (0.986, SE = 0.015) than monthly survival at other times (0.964, SE = 0.006). Survival of adult males varied among years and with a general seasonal trend inverse to that for females. An index of body condition was positively related to survival of adult females in fall and spring, but not for adult males or immature geese. Monthly survival of immatures was lower during their first hunting season (0.886, SE = 0.026) than during all subsequent seasons (0.963, SE = 0.007). Annual survival of immatures beginning 1 October, immediately before the hunting season, was 0.471. Corresponding variations in survival rates, population numbers, and hunting regulations suggest that hunting may have influenced survival in this population of greater white-fronted geese.

Geographic, temporal, and age-specific variation in diets of Glaucous Gulls in western Alaska

We collected boluses and food remains of adult Glaucous Gulls (Larus hyperboreus) at or near nests and chicks, and digestive tracts from adults at three sites on the Yukon-Kuskokwim Delta, Alaska that differed in proximity to marine and terrestrial foods. We observed both geographic and temporal variation in diet; gulls consumed proportionately more terrestrial prey after peak hatch in late June, and gulls near the coast consumed proportionately more marine prey than gulls at two inland areas. Goslings occurred in > 60% of all samples from these inland areas. We compared these data to those from a previous study in western Alaska and found no marked differences. Evidence for similar patterns of geographic and temporal variation in diet was found using measurements of stable-carbon and nitrogen isotopes in gull and prey tissues. Stable isotope analysis further revealed that adult gulls consumed proportionately more marine prey (saffron cod, Eleginus gracilis) than they fed to their young. Using isotopic models, we estimated that 7-22% and 10-23% of the diet of adult and juvenile Glaucous Gulls, respectively, was comprised of terrestrial species. In addition to significant age-related variation, dietary estimates varied among geographic areas and between pre- and post-hatch periods. Overall, our isotopic estimates of the contribution of terrestrial prey to the diet of Glaucous Gulls was less than what may be inferred from conventional methods of diet analysis. Our study emphasizes the benefit of combining stable-isotope and conventional analyses to infer temporal and geographic changes in diet of wild birds and other organism.

An adaptive-management framework for optimal control of hiking near golden eagle nests in Denali National Park.

Unintended effects of recreational activities in protected areas are of growing concern. We used an adaptive-management framework to develop guidelines for optimally managing hiking activities to maintain desired levels of territory occupancy and reproductive success of Golden Eagles (Aquila chrysaetos) in Denali National Park (Alaska, U.S.A.). The management decision was to restrict human access (hikers) to particular nesting territories to reduce disturbance. The management objective was to minimize restrictions on hikers while maintaining reproductive performance of eagles above some specified level. We based our decision analysis on predictive models of site occupancy of eagles developed using a combination of expert opinion and data collected from 93 eagle territories over 20 years. The best predictive model showed that restricting human access to eagle territories had little effect on occupancy dynamics. However, when considering important sources of uncertainty in the models, including environmental stochasticity, imperfect detection of hares on which eagles prey, and model uncertainty, restricting access of territories to hikers improved eagle reproduction substantially. An adaptive management framework such as ours may help reduce uncertainty of the effects of hiking activities on Golden Eagles.

TEMPORAL AND GEOGRAPHIC VARIATION IN SURVIVAL OF JUVENILE BLACK BRANT

Abstract First-year survival has important implications for the structure and growth of populations. We examined variation in seasonal survival of first-year Pacific Black Brant (Branta bernicla nigricans) marked late in summer in Alaska at two brood-rearing areas on the Yukon-Kuskokwim Delta (Tutakoke and Kokechik) and one area on the Arctic Coastal Plain to provide insight into the magnitude and timing of mortality during fall migration. First-year survival was lower in early fall (15 July–1 October), when birds fledged from brood-rearing areas and migrated to their primary fall staging area at Izembek Lagoon, Alaska, than during late fall and early winter (1 October–15 February), when birds made a long-distance transoceanic flight (>5000 km) to wintering areas in Baja California, Mexico. When compared to other years, monthly survival during early fall was 20–24% lower in 1992, the year of latest hatch dates and slowest growth of goslings. There was strong evidence to indicate that survival varied geographically within the early fall period. Monthly survival estimates during early fall were lowest for birds from Tutakoke, highest for birds from the Arctic Coastal Plain, and intermediate at Kokechik. Our findings revealed that most juvenile mortality occurred during the first 2 months following banding, and variation in juvenile survival during this period was likely influenced significantly by environmental parameters and habitat conditions on the breeding grounds. Monthly survival estimates during the subsequent 4 months were similar across geographic areas, and long-distance migration was likely the most important contributor to juvenile mortality during this period. Variación Temporal y Geográfica en la Supervivencia de Juveniles de Branta bernicla nigricans Resumen. La supervivencia durante el primer año de vida tiene implicancias importantes para la estructura y el crecimiento de las poblaciones. Examinamos la variación en la supervivencia estacional en individuos añales de Branta bernicla nigricans marcados al final del verano en Alaska en dos áreas de cría del Delta Yukon-Kuskokwim (Tutakoke y Kokechik) y un área en la planicie costera ártica para brindar información sobre la magnitud y el esquema temporal de mortalidad durante la migración de otoño. La supervivencia durante el primer año fue menor a principios del otoño (15 July–1 October), cuando las aves abandonaron las áreas de cría y migraron hacia el área principal de permanencia otoñal en Izembek Lagoon, Alaska, que durante fines de otoño y comienzos del invierno (1 October–15 February), cuando las aves realizaron un vuelo transoceánico de larga distancia (>5000 km) hacia las áreas de invernada en Baja California, México. Comparando con otros años, la supervivencia mensual durante principios del otoño fue un 20–24% menor en 1992, el año con fechas más tardías de eclosión y con crecimiento más lento de los polluelos. Hubo fuerte evidencia para indicar que la supervivencia varió geográficamente a principios del otoño. Las estimaciones mensuales de supervivencia durante principios del otoño fueron menores para las aves de Tutakoke, mayores para las aves de la planicie costera ártica, e intermedias para Kokechik. Nuestros resultados revelaron que la mayoría de la mortalidad juvenil ocurrió durante los dos primeros meses luego del anillado, y la variación en la supervivencia de los juveniles durante este período fue probablemente influenciada de forma significativa por parámetros ambientales y condiciones del hábitat en las áreas de cría. Las estimaciones mensuales de supervivencia durante los cuatro meses siguientes fueron similares para las distintas áreas geográficas, y la migración de larga distancia fue probablemente la causa más importante de mortalidad juvenil durante este período.