Alan D. Afton

BIOENERGETICS OF BREEDING NORTHERN SHOVELERS: DIET, NUTRIENT RESERVES, CLUTCH SIZE, AND INCUBATION'

We analyzed food habits, digestive organs, and nutrient reserves (lipid, protein, and mineral) of male and female Northern Shovelers (Anas clypeata) nesting in southern Manitoba. We studied shovelers because, on an annual basis, they consume more animal matter than do other Anas spp. Thus, they are ideal subjects for testing the hypothesis that the inability of female ducks to obtain animal protein during egg laying limits clutch size. Predictably, we found that, during prelaying and laying, males and females primarily ate aquatic invertebrates. Despite this, the intestine lengths of breeding shovelers, particularly of females, are longer than those of many other waterfowl, which may be a response to an energy-deficient diet. Nutrient reserves of males changed little during prelaying and laying. Lipid reserves of females, on average, declined by 0.72 g for every 1 g of lipid that they deposited in eggs. Furthermore, in females that had laid 2 five eggs, there was a positive correlation (+0.60) between number of developing ovarian follicles and size of lipid reserves. Remarkably, however, the protein reserves of females increased by 0.1 g for every 1 g of protein committed to reproductive tissue. Mineral reserves were unrelated to eggshell pro- duction. The decline in lipid and protein reserves of incubating females could account for 26% of their energy requirements during that period. The protein : lipid ratio in shoveler diets was about 14: 1, whereas that in the reproductive tissue (eggs and oviduct) was near unity. Thus, we argue that lipid reserves, not protein acquisition, limit clutch size of shovelers and also that the importance of protein to tem- perate-nesting waterfowl has been overemphasized. We conclude that most intraspecific variation in clutch size of waterfowl is proximately caused and, thus, that few females lay the optimum clutch size, i.e., the average clutch size is not directly a product of natural selection, and probably reflects nutrients available to the average female.

Declining scaup populations : A retrospective analysis of long-term population and harvest survey data

We examined long-term databases concerning population status of scaup (lesser [Aythya affinis] and greater scaup [A. marila] combined) and harvest statistics of lesser scaup to identify factors potentially limiting population growth. Specifically, we explored evidence for and against the general hypotheses that scaup populations have declined in association with declining recruitment and/or female survival. We examined geographic heterogeneity in scaup demographic patterns that could yield evidence about potential limiting factors. Several biases exist in survey methodology used to estimate scaup populations and harvest statistics; however, none of these biases likely accounted for our major findings that (1) the continental scaup breeding population has declined over the last 20 years, with widespread and consistent declines within surveyed areas of the Canadian western boreal forest where most lesser scaup breed; (2) sex ratios of lesser scaup in the U.S. harvest have increased (more males now relative to females); and (3) age ratios of lesser scaup in the U.S. harvest have declined (fewer immatures now relative to adults), especially in the midcontinent region. We interpreted these major findings as evidence that (1) recruitment of lesser scaup has declined over the last 20 years, particularly in the Canadian western boreal forest; and (2) survival of female lesser scaup has declined relative to that of males. We found little evidence that harvest was associated with the scaup population decline. Our findings underscore the need for both improvements and changes to population survey procedures and new research to discriminate among various hypotheses explaining the recent scaup population decline.

Data set incongruence and correlated character evolution : an example of functional convergence in the hind-limbs of stifftail diving ducks

The unwitting inclusion of convergent characters in phylogenetic estimates poses a serious problem for efforts to recover phylogeny. Convergence is not inscrutable, however, particularly when one group of characters tracks phylogeny and another set tracks adaptive history. In such cases, convergent characters may be correlated with one or a few functional anatomical units and readily identifiable by using comparative methods. Stifftail ducks (Oxyurinae) offer one such opportunity to study correlated character evolution and function in the context of phylogenetic reconstruction. Morphological analyses place stifftail ducks as part of a large clade of diving ducks that includes the sea ducks (Mergini), Hymenolaimus, Merganetta, and Tachyeres, and possibly the pochards (Aythyini). Molecular analyses, on the other hand, place stifftails far from other diving ducks and suggest, moreover, that stifftails are polyphyletic. Mitochondrial cytochrome b gene sequences of eight stifftail species traditionally supposed to form a clade were compared with each other and with sequences from 50 other anseriform and galliform species. Stifftail ducks are not the sister group of sea ducks but lie outside the typical ducks (Anatinae). Of the four traditional stifftail genera, monophyly of Oxyura and its sister group relationship with Nomonyx are strongly supported. Heteronetta probably is the sister group of that clade, but support is weak. Biziura is not a true stifftail. Within Oxyura, Old World species (O. australis, O. leucocephala, O. maccoa) appear to form a clade, with New World species (O. jamaicensis, O. vittata) branching basally. Incongruence between molecules and morphology is interpreted to be the result of adaptive specialization and functional convergence in the hind limbs of Biziura and true stifftails. When morphological characters are divided into classes, only hind-limb characters are significantly in conflict with the molecular tree. Likewise, null models of synonymous and nonsynonymous substitution based on patterns of codon-degeneracy and chemical dissimilarity indicate that the nucleotide and amino acid changes postulated by the molecular tree are more plausible than those postulated by the morphological tree. These findings teach general lessons about the utility of highly adaptive characters (in particular those related to foraging ecology) and underscore the problems that convergence can pose for attempts to recover phylogeny. They also demonstrate how the concept of natural data partitions and simple models of evolution (e.g., parsimony, likelihood, neutrality) can be used to test the accuracy of independent phylogenetic estimates and provide arguments in favor of one tree topology over another.

NUTRIENT-RESERVE DYNAMICS OF BREEDING LESSER SCAUP: A TEST OF COMPETING HYPOTHESES

We analyzed nutrient reserves (lipid, protein, mineral) and organs of Lesser Scaup (Aythya afinis) breeding in southwestern Manitoba. Our analysis provided weak support for the hypothesis that paired males are physically superior to those pairing later or not at all. Protein reserves of paired males were larger than those of unpaired males, whereas fat and mineral reserves were similar in size between pair-status groups. Except for a marked decline in lipid reserves, body components and organs of paired males changed little while on breeding areas before laying by their mates. Nutrient reserves of males also did not change relative to the nutrient commitment to reproduction by their mates. Females accumulated protein and mineral reserves and at least maintained lipid reserves while on breeding areas before laying. Lipid reserves of females declined, on average, 0.5 g for every 1 g of lipid deposited in eggs. Mineral reserves declined, on average, 0.1 g for every 1 g of egg shell produced. Declines in nutrient reserves of incubating females could account for 12% of their energy requirements during that period. Lipid-reserve dynamics of females were consistent with predictions of the lipid-limitation hypothesis, but contradicted those ofthe protein-limitation and migrational-uncertainty hypotheses. Food availability on breeding areas may limit lipid storage by females, and serve as an important proximate factor affecting clutch size of Lesser Scaup.

Timing of nest searches for upland nesting waterfowl

Searches for duck nests should maximize the probability of locating nests, while minimizing the possibility of causing nest abandonment. Thus, we collected nest attendance data for 44 mallard (Anas platyrhynchos), 13 blue-winged teal (A. discors), 12 lesser scaup (Aythya affinis), 8 northern shoveler (Anas clypeata), 6 gadwall (A. strepera), and 4 green-winged teal (A. crecca) females to determine the optimal times of day to search for active nests. Females of most species attended nests from 0800 to 1400 central standard time (CST). The overall probability of nest attendance during this time was 91.4 ± 2.6 (SE) %. Consequently, nest searches for upland nesting waterfowl should be initiated after 0800 and should be terminated by 1400 CST

NUTRIENT RESERVES OF LESSER SCAUP (AYTHYA AFFINIS) DURING SPRING MIGRATION IN THE MISSISSIPPI FLYWAY: A TEST OF THE SPRING CONDITION HYPOTHESIS

Abstract The continental scaup population (Lesser [Aythya affinis] and Greater [A. marila] combined) has declined markedly since 1978. One hypothesis for the population decline states that reproductive success has decreased because female scaup are arriving on breeding areas in poorer body condition than they did historically (i.e. spring condition hypothesis). We tested one aspect of that hypothesis by comparing body mass and nutrient reserves (lipid, protein, and mineral) of Lesser Scaup at four locations (Louisiana, Illinois, Minnesota, and Manitoba) between the 1980s and 2000s. We found that mean body mass and lipid and mineral reserves of females were 80.0, 52.5, and 3.0 g higher, respectively, in the 2000s than in the 1980s in Louisiana; similarly, body mass and lipid and mineral reserves of males were 108.8, 72.5, and 2.5 g higher, respectively. In Illinois, mean body mass and lipid reserves of females were 88.6 and 56.5 g higher, respectively, in the 2000s than in the 1980s; similarly, body mass and lipid and mineral reserves of males were 80.6, 76.0, and 2.7 g higher, respectively. Mean body mass of females were 58.5 and 58.9 g lower in the 2000s than in the 1980s in Minnesota and Manitoba, respectively; mean body mass of males, similarly, were 40.7 g lower in Minnesota. Mean lipid reserves of females in the 2000s were 28.8 and 27.8 g lower than those in the 1980s in Minnesota and Manitoba, respectively. Mean mineral reserves of females in the 2000s were 3.2 g lower than those in the 1980s in Manitoba. Consequently, females arriving to breed in Manitoba in the 2000s had accumulated lipid reserves for 4.1 fewer eggs and mineral reserves for 0.8 fewer eggs than those arriving to breed there in the 1980s. Accordingly, our results are consistent with the spring condition hypothesis and suggest that female body condition has declined, as reflected by decreases in body mass, lipids, and mineral reserves that could cause reductions in reproductive success and ultimately a population decline.

Forced copulation results in few extrapair fertilizations in Ross’s and lesser snow geese

Extrapair paternity varies from 0 to over 70% of young among various populations of birds. Comparative studies have suggested that this variation is related to nesting density, breeding synchrony and the proportion of extrapair copulations. We used minisatellite DNA fingerprinting to examine levels of extrapair paternity in Rosss geese, Chen rossi, and lesser snow geese, C. caerulescens c. (hereafter snow geese) nesting in the largest known goose colony in the world. These geese have one of the highest known percentages of extrapair copulation (46-56% of all attempted copulations), and all of these appeared to be forced. Among all successful copulations, 33 and 38% were extrapair in Rosss and snow geese, respectively. Despite the high percentage of extrapair copulations, extrapair paternity was low in both Rosss and snow geese (2-5% of young). Extrapair paternity was not related to nest density in either species. However, in snow geese, extrapair paternity was more likely to occur in nests of females that nested asynchronously, either early or late in the season. This is one of a few reported examples of a negative relationship between extrapair paternity and breeding synchrony. Extrapair young also tended to come from eggs laid later in the clutch. Although forced extrapair copulations appear to be a relatively inefficient reproductive tactic for males, they may provide a reproductive advantage for some males. Copyright 1999 The Association for the Study of Animal Behaviour.

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. Estudiamos 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.

Use of Habitats by Female Northern Pintails Wintering in Southwestern Louisiana

The breeding population of northern pintails (Anas acuta) in 1996 was 39% below the long-term average. Because winter habitat quality may influence subsequent breeding population size in pintails, identification of habitats used by wintering pintails and factors influencing use of habitats may be important for managing for population increase. We examined variation in diel use of habitats by radiotagged female pintails (n = 272) in southwestern Louisiana in relation to age (imm and ad), winter (1991-92 and 1992-93), and time period within winters (pre-hunting season, first hunting season, time between split hunting seasons, second hunting season, and post-hunting season). Diurnal use of refuges was significantly greater during hunting seasons than during immediately preceding or succeeding nonhunting seasons. Consequently, we reject Tamisiers (1976) hypothesis that high diurnal use of refuges by pintails in southwestern Louisiana occurs independent of hunting. Nocturnal use of refuges was low (<14%) during all time periods, and declined later in winters. Time-period differences in diurnal and nocturnal use of habitats (large permanent pools, marsh, rice, fallow [idle], and other agriculture [primarily soybeans]) were not consistent between winters. Diel use of refuges or habitats did not differ in relation to female age. Females used fallow and rice agriculture extensively, particularly at night, and these habitats collectively accounted for 68-93% of nocturnal use. Differential use of habitats between winters was related to annual differences in relative abundances of rice and fallow agriculture. Proximity of refuges to agricultural areas should be an important management consideration for wintering pintails and other waterfowl.

Direct recovery rates of lesser scaup banded in northwest Minnesota : Sources of heterogeneity

Heterogeneity in direct recovery rates is an important area of study because deductions about survival rates and hunting mortality are made from recovery data. We tested the hypothesis of condition bias in hunter-killed lesser scaup (Aythija affinis) and tested differences among direct recovery rates (f= proportion of birds banded that are killed by a hunter ≤3 months after release and reported) of scaup staging on Thief Lake Wildlife Management Area (TLWMA) and Agassiz National Wildlife Refuge (ANWR) in northwestern Minnesota Scaup were trapped, held for 24 hr, weighed, banded with standard aluminum leg bands, and released during 4 October-8 November 1983-86 at TLWMA, and 1984-86 at ANWR. During 1984-86 e also sprayed areas of white plumage with fluorescent paint, colorcoded by age and location. Recovery data obtained from cooperative hunters and the U.S. Geological Survey Bird Banding Laboratory were subjectec to 3 sets of analyses. In an analysis of variance (ANOVA), after adjusting for sex, age, year, location of capture, and date of capture body mass at capture of recovered birds was lower, on average, than those not recovered Logistic regression mdicated (1) probability of recovering a bird decreased with increasing body mass; (2) within years, probability of recovery increased with date of first capture; (3) scaup at TLWMA were recovered at greater rates than scaup at ANWR: (4) hatching-year (HY) scaup were recovered at greate r rates than were after-hatcbing-year (AHY) birds; and (5) recovery was more likely during 1984-86 than in 1983. Finally, in a crude test of recovery distribution, recoveries of birds banded at ANWR were about half as likely as those banded on TLWMA to occur in Minnesota. We conclude that cohort membership (age, capture site) and condition, as measured by body mass, influence susceptibility to hunting mortalitv. These and other sources of heterogeneity in recovery rates should be considered when modeling survival of scaup.