James B. Grand

Factors influencing depredation of artificial duck nests

Because artificial nests can facilitate controlled experiments of nest success, we used them to assess whether human visitation, nest density, vegetation structure, and proximity to habitat edge could affect depredation of duck nests on Yukon Flats National Wildlife Refuge, Alaska. More (P 0.05) between depredated and undisturbed nests

Intraspecific Variation in Nutrient Reserve Use During Clutch Formation by Lesser Scaup

Abstract We studied nutrient reserve dynamics of female Lesser Scaup (Aythya affinis) to identify sources of intraspecific variation in strategies of nutrient acquisition for meeting the high nutritional and energetic costs of egg formation. We collected data from interior Alaska and combined these with data for Lesser Scaup from midcontinent breeding areas (Afton and Ankney 1991), allowing a rangewide analysis for the species. We found little evidence that nutrient reserve use differed between Alaskan and midcontinent Lesser Scaup, except that subarctic birds used a small amount of protein reserves when forming eggs, whereas midcontinent birds did not. Mineral reserves contributed relatively little to the clutch, but endogenous lipid accounted for approximately two-thirds of the lipid in the clutch. Levels of endogenous lipid and protein at initiation of clutch formation declined with date of initiation. Also, absolute amounts of lipid and protein reserves used declined through the season, corresponding to smaller clutch sizes. Our data are consistent with a seasonally variable threshold of lipid reserves for initiation of clutch formation and considerable reliance on lipid reserves, suggestive of lipid control of productivity via effects on clutch size and initiation dates. However, our data cannot refute the hypothesis that clutch size or initiation dates are set by other factors that in turn dictate the amount of lipid reserves that are stored and used. Despite uncertainty regarding the role of nutrient limitations on productivity, maintenance of adequate food resources on winter, migration, and breeding areas should be a management concern, given the high costs of clutch formation by Lesser Scaup, evidence of recent population declines, and potential links between nutrition and productivity. Variación Intraespecífica en el Uso de las Reservas de Nutrientes durante la Formación de Huevos en Aythya affinis Resumen.u2003Estudiamos la dinámica en la reserva nutricional de hembras de Aythya affinis para identificar fuentes de variación intraespecífica en las estrategias de adquisición de nutrientes. Estos nutrientes permiten afrontar los altos costos nutricionales y energéticos que demanda la producción de huevos. Colectamos datos en el interior de Alaska y los combinamos con información sobre A. affinis para áreas de cría del centro del continente (Afton y Ankney 1991), permitiendo un análisis para una extensa área de distribución de la especie. Encontramos escasa evidencia sobre variaciones en el uso de nutrientes de reserva entre A. affinis de Alaska y del centro del continente. Como excepción, las aves subárticas usaron una pequeña cantidad de las reservas proteicas cuando produjeron los huevos, en contraposición con las aves del centro del continente que no las usaron. Las reservas minerales contribuyeron relativemente poco a la formación de huevos, pero los lípidos endógenos representaron casi dos-tercios de los lípidos presentes en los huevos. Los niveles de lípidos endógenos y de proteínas al comienzo de la producción de huevos disminuyeron en relación con la fecha de inicio. Además, las cantidades absolutas de reserva de lípidos y proteínas usadas disminuyeron a lo largo de la estación, correspondiéndose con nidadas más pequeñas. Nuestros datos son consistentes con la existencia de un umbral estacional variable en las reservas de lípidos que determina el inicio de la formación de huevos, y con la seguridad relativa que ofrecen las reservas de lípidos. Estos resultados sugieren que los lípidos controlan la productividad de las aves a través de efectos sobre el tamaño de la nidada y la fecha de inicio. Sin embargo, nuestros datos no pueden refutar la hipótesis que el tamaño de la nidada o la fecha de inicio estén determinados por otros factores que a su vez determinen la cantidad de reservas de lípidos que son almacenadas y usadas. A pesar de las dudas sobre el rol que juega la limitación de nutrientes sobre la productividad, las estrategias de manejo deberían considerar el mantenimiento de reservas alimenticias adecuadas en áreas de invernada, migración y reproducción. Esto se justifica dado el alto costo que representa para A. affinis la producción de huevos, la evidencia sobre recientes disminuciones poblacionales, y los vínculos potenciales entre nutrición y productividad.

Effect of lead poisoning on spectacled eider survival rates

Spectacled eider (Somateria fischeri) populations on the Yukon-Kuskokwim Delta (Y-K Delta), Alaska, declined rapidly through the 1980s, and low adult female survival was suggested as the likely cause of the decline. We used mark-resighting techniques to study annual survival rates of adult female spectacled eiders at 2 sites on the Y-K Delta during 1993-96. Our data suggest survival rates may differ among sites. However, a model fit to a subset of data on females for which we knew lead levels in blood suggests lead exposure influences survival. Adult females exposed to lead prior to hatching their eggs survived at a much lower rate (0.44 ± 0.10) each year than females not exposed to lead before hatch (0.78 ± 0.05). We suggest most mortality from lead exposure occurs over winter, and the related reduction in adult survival may be impeding recovery of local populations. We encourage managers to curtail input of lead shot into the environment.

A model of northern pintail productivity and population growth rate

Our objective was to synthesize individual components of reproductive ecology into a single estimate of productivity and to assess the relative effects of survival and productivity on population dynamics. We used information on nesting ecology, renesting potential, and duckling survival of northern pintails (Anas acuta) collected on the Yukon-Kuskokwim Delta (Y-K Delta), Alaska, 1991-95, to model the number of ducklings produced under a range of nest success and duckling survival probabilities. Using average values of 25% nest success, 11% duckling survival, and 56% renesting probability from our study population, we calculated that all young in our population were produced by 13% of the breeding females, and that early-nesting females produced more young than later-nesting females. Further, we calculated, on average, that each female produced only 0.16 young females/nesting season. We combined these results with estimates of first-year and adult survival to examine the growth rate (λ) of the population and the relative contributions of these demographic parameters to that growth rate. Contrary to aerial survey data, the population projection model suggests our study population is declining rapidly (λ = 0.6969). The relative effects on population growth rate were 0.1175 for reproductive success, 0.1175 for first-year survival, and 0.8825 for adult survival. Adult survival had the greatest influence on λ for our population, and this conclusion was robust over a range of survival and productivity estimates. Given published estimates of annual survival for adult females (61%), our model suggested nest success and duckling survival need to increase to approximately 40% to achieve population stability. We discuss reasons for the apparent discrepancy in population trends between our model and aerial surveys in terms of bias in productivity and survival estimates.

Variation in egg size of the northern pintail

Egg size is an important determinant of reproductive investment by birds. For many species, total investment in a clutch is limited by the size of stored reserves (Ankney and MacInnes 1978, Esler and Grand 1994a). Egg size determines the unit by which these stored reserves are partitioned. Individual females in most species of waterfowl show a high repeatability for egg size, implying that individuals either cannot, or do not, alter their egg size in response to varying environmental conditions (Batt and Prince 1979, Duncan 1987, Laurila and Hario 1988, Lessells et al. 1989, Flint and Sedinger 1992). Thus differences in egg size appear to represent different reproductive strategies among individuals. Fitness can be measured by the number of offspring an individual contributes to a population. Egg size may be related to fitness in some species of waterfowl as young from larger eggs are better able to survive extreme conditions (Ankney 1980, Thomas and Brown 1988). Birds laying larger clutches are almost always more fit as they fledge more young (Lessells 1986, Rockwell et al. 1987, Flint 1993). These fitness patterns create the potential for a trade-off between clutch size and egg size where females laying large clutches of small eggs have the same fitness as females laying smaller clutches of large eggs. The fact that Northern Pintails (Anas acuta) utilize stored reserves (Mann and Sedinger 1993, Esler and Grand 1994a) and have a high repeatability for egg size (i.e., egg size is fixed) (Duncan 1987), makes them candidates to engage in clutch sizeegg size trade-offs (Rohwer 1988, Rohwer and Eisenhauer 1989). An inverse relationship between egg size and clutch size would be indicative of a phenotypic trade-off among these fitness components. Our goal in this study was to describe egg size variation in Northern Pintails (hereafter pintails) with regard to female age, body size, clutch size, year, initiation date, and nesting attempt. We compare our results to those from other populations of nesting pintails and discuss whether phenotypic clutch size-egg size trade-offs exist for pintails.

Allocation of Limited Reserves to a Clutch: A Model Explaining the Lack of a Relationship between Clutch Size and Egg Size

Lack (1967, 1968) proposed that clutch size in waterfowl is limited by the nutrients available to females when producing eggs. He suggested that if nutrients available for clutch formation are limited, then species producing small eggs would, on average, lay more eggs than species with large eggs. Rohwer (1988) argued that this model also should apply within species. Thus, the nutrient-limitation hypothesis predicts a tradeoff among females between clutch size and egg size (Rohwer 1988). Field studies of single species consistently have failed to detect a negative relationship between clutch size and egg size (Rohwer 1988, Lessells et al. 1989, Rohwer and Eisenhauer 1989, Flint and Sedinger 1992, Flint and Grand 1996). The absence of such a relationship within species has been regarded as evidence against the hypothesis that nutrient availability limits clutch size (Rohwer 1988,1991, 1992; Rohwer and Eisenhauer 1989). Failure to detect a negative correlation between clutch size and egg size is not necessarily evidence against regulation of clutch size by nutrient reserves. If both clutch size and egg size are correlated with a third variable, then variation in the third variable could conceal a correlation between clutch size and egg size at the population level. In this paper we discuss evidence that both nutrient reserves and egg size are positively correlated with body size for species that rely on reserves for egg production, and we explore how these correlations might influence detection of tradeoffs between clutch size and egg size. We have assumed that individual females have a fixed amount of reserves available for the entire reproductive attempt (i.e. clutch formation and incubation) and a phenotypically fixed egg size. Waterfowl, in general, show high repeatability of egg size, suggesting that females cannot (or do not) alter their egg size in response to nutrient reserves or environmental conditions (e.g. Flint and Grand 1996). Reserves are used for egg production, but optimal investment in the clutch is less than the maximum possible (Fig. 1) because reserves are retained for use during incubation (Klomp 1970, Ryder 1970, Raveling 1979, Ankney 1984, Ankney and Alisauskas 1991, Gloutney and Clark 1991, Afton and Paulus 1992, Er-