Aythya Affinis Research Articles

Eye Colour, Aging, and Decoy Trap Bias in Lesser Scaup, <em>Aythya affinis</em>

Researchers routinely assume that samples of trapped or captured animals are representative of the overall population, though these assumptions are not always evaluated. We used decoy-trapped Lesser Scaup (Aythya affinis) to assess the reliability of classifying females as yearlings or adults from a distance, based on documented age-related eye-colour changes, and also to evaluate the presence of sex, condition and age biases in decoy trapping. We compared eye colour of trapped females to photographs of known-age females following a published procedure while females were (1) in traps (by using spotting scopes or binoculars) and (2) in-hand. Assuming in-hand age assessments were correct, we found that adults aged from a distance were frequently misclassified as yearlings, but yearlings were never misclassified as adults. Distance between observer and female, overall observation quality, and cloud cover did not influence age assignment success. A larger proportion of males was captured than observed during a survey of the local breeding population. We also found that decoy-trapped females had lower body mass and were more likely to be yearlings compared to pass- and jump-shot females from the same area. We conclude that female Lesser Scaup cannot be accurately aged from a distance using eye colour and concur with other researchers that possible sex, age and condition biases should be evaluated when using decoy traps.

Patterns of prey use by lesser scaup Aythya affinis (Aves) and diet overlap with fishes during spring migration

Recent decline in the lesser scaup Aythya affinis population has been linked to changes in wetland conditions along their spring migration routes. In particular, the use of amphipod prey by lesser scaup has declined in many regions of the upper Midwest U.S.A. and has been linked to expanded fisheries, although empirical data on diet overlap are lacking. To explore patterns of prey use by lesser scaup and diet overlap with fishes, we quantified diets of scaup and fishes during the 2003 and 2004 spring migration in eastern South Dakota, U.S.A. We compared diet overlap between lesser scaup and fishes collected from Twin Lakes, South Dakota—an important stopover location for spring-migrating scaup. Plant seeds occurred in >95% of lesser scaup diets (n = 118) and represented an appreciable amount of consumed biomass (>70%). Gastropods, amphipods, and chironomids were the most abundant invertebrate prey taxa and occurred in 29–34% of lesser scaup diets. Although relatively frequent, these taxa each contributed only 4–27% of the diet by weight. Percent dry mass of amphipods, a preferred prey by lesser scaup, was low (4%) indicating that amphipod availability may be reduced during spring migration. Analysis of fish diets showed that black bullhead Ameiurus melas and yellow perch Perca flavescens had the highest diet overlap with lesser scaup at 94% and 92%, respectively. Moreover, mean size of amphipods and chironomids found in fish diets were significantly larger than that consumed by lesser scaup. Our findings support the notion that amphipod use by spring-migrating lesser scaup has declined and that size-selective predation by fishes may influence prey availability for lesser scaup.

Contaminants in Lesser Scaup Eggs and Blood from Yukon Flats National Wildlife Refuge, Alaska

AbstractDocumented declines in Lesser Scaup (Aythya affinis) populations may be caused by several factors, including reduced reproductive success or survival from exposure to environmental contaminants during winter, migration, or breeding. We evaluated organochlorines and inorganic elements in Lesser Scaup blood (n = 14) and eggs (n = 10) from a breeding area in the relatively pristine Yukon Flats National Wildlife Refuge in interior Alaska. Most contaminants were not at concentrations of concern. Lead was detected in only four blood samples, with an average when detected (0.29 mg kg−1 wet weight [ww]) slightly above background levels (0.20 mg kg−1 ww). Our study area had little or no hunting, but since lead exposure is correlated with hunting pressure, lead should be evaluated in other Lesser Scaup breeding areas. Strontium in eggs (mean = 10.90 mg kg−1 dry weight [dw]) was significantly negatively correlated with eggshell thickness. Eggshell thickness was also 18% lower than in museum specimens, a percentage associated with population declines in other species, and was not correlated with other contaminants. Few comparative data in the literature exist, but productivity in this breeding area was low (mean nest success = 12%), so further research on the effects of strontium on productivity through the mechanism of eggshell thinning is needed. Most environmental contaminants are unlikely to be affecting Lesser Scaup populations breeding in interior Alaska, but lead and strontium should be studied further.

Effects of Cadmium, Mercury, and Selenium on Reproductive Indices in Male Lesser Scaup (Aythya affinis) in the Western Boreal Forest

Combined lesser scaup (Aythya affinis) and greater scaup (A. marila) populations decreased from the 1980s to the 1990s and have not recovered. Factors limiting reproduction, including effects of contaminants and trace elements, have been highlighted as a concern in female scaup, but no studies have examined possible effects on male scaup. We examined the effects of cadmium, mercury, selenium, and corticosterone on pair status and on male reproductive indices, including testosterone, testes mass, and seminiferous tubule diameter, in male lesser scaup collected in the western boreal forest near Yellowknife, Northwest Territories, May and June, during 2004 and 2005. Male scaup that were larger in size (p = 0.048) and with better body condition (p = 0.038) were more likely to be paired. No relations were observed between independent variables and testosterone and testes mass. However, results suggested that seminiferous tubule diameter is influenced by a complex array of biologic and toxicologic parameters, which differ depending on pair status. Tubule diameters of paired male scaup were negatively influenced by hormones, whereas contaminants influenced diameter in unpaired male scaup. The effects of selenium were attenuated when bound with cadmium but not mercury. When selenium concentrations were high (greater than median value), there was a positive effect of cadmium on tubule diameter (R(2) = 0.30, n = 10, p = 0.007) but a negative relation with mercury (R(2) = 0.15, n = 10, p = 0.09). Seminiferous tubule diameter may be a sensitive indicator of sublethal effects of contaminants. This study showed contaminant and trace element effects at concentrations lower than threshold levels associated with major toxic effects. This study also demonstrated the complex nature of biologic systems and the importance of considering interactions to accurately characterize effects of metals.

Is selenium affecting body condition and reproduction in boreal breeding scaup, scoters, and ring-necked ducks?

Elevated levels of selenium (Se) have been detected in wintering and spring-staging lesser scaup. Here, we compared spring scaup Se and mercury (Hg) levels to those of ring-necked ducks and white-winged scoters, species exhibiting increasing and decreasing boreal populations, respectively. Mercury concentrations were low in all three species. Geometric mean (95%CI) liver Se concentrations were 6.2 (5.5–7.0), 4.6 (4.0–5.4), and 32.6 (28.4–37.3) mg/kg dry weight (dw) in scaup, ringnecks and scoters, respectively. Only scoter livers (66%) were above 33 mg/kg dw Se. Scaup and ringneck Se levels were unrelated to breeding status or lipid and protein levels; breeding scoters and females with greater lipid mass had higher Se than non-breeders. Egg and follicle concentrations in scaup and scoters were normal (mean [95%CI] = 2.3 [1.9–2.6] and 2.4 [2.1–2.7] mg/kg dw, respectively). Overall, we found no support for a relationship between selenium and boreal scaup and scoter declines, and discuss current Se threshold concentrations.

Chromium and Selenium in Invertebrate Prey of Lesser Scaup

Abstract: The combined lesser scaup (Aythya affinis) and greater scaup (A. marila) population in North America has steadily declined from an average of 7.5 million breeding birds in the 1970s to an all‐time low of 3.39 million in 2005. Bioaccumulation is widely known as the means of elevated levels of toxins in vertebrates. Our goal was to determine whether chromium and selenium were factors contributing to the continental scaup population decline by identifying wetlands used by scaup that potentially contain dangerous concentrations of chromium and selenium. We hypothesized that zebra mussels (Dreissena polymorpha) would contain the highest concentrations of selenium and chromium because they are filter feeders, whereas amphipods would contain the lowest concentrations because of their short life span. We collected zebra mussels, fingernail clams (Sphaerium transversum), chironomid larvae, snails (Gastropoda), and amphipods on randomly selected traditional lesser scaup staging and breeding wetlands. We found higher chromium concentrations in zebra mussels from Iowa, USA, than in those from Wisconsin, USA (P = 0.0074). In addition, selenium concentrations in zebra mussels from Wisconsin were higher than in those from Iowa (P < 0.0001). Higher selenium concentrations in amphipods were associated with sampled wetlands surrounded by developed land. Invertebrates with >5 μg/g selenium and >1 μg/g chromium are potentially hazardous for scaup. Chromium concentrations in Iowa were the highest for most species examined, whereas they were the lowest in Minnesota, USA. Based on our results, lesser scaup probably accumulate the highest concentrations of selenium on Lake Onalaska, Wisconsin, whereas they probably accumulate the lowest concentrations in Iowa. Waterfowl biologists are searching for explanations to the scaup decline; we propose chromium and selenium concentrations in amphipods and fingernail clams may be a factor.

Relationships of cadmium, mercury, and selenium with nutrient reserves of female lesser scaup (Aythya affinis) during winter and spring migration

Trace elements may have important effects on body condition of ducks during spring migration, because individuals are experiencing energetically costly events (e.g., migration, nutrient reserve accumulation, pair formation, feather molt, and ovarian follicle development). We examined relationships among hepatic cadmium, mercury, and selenium concentrations (microg/g dry wt) and nutrient reserves (lipid, protein, and mineral) of female lesser scaup (Aythya affinis) during winter and spring migration at four locations within the Mississippi Flyway (LA, IL, and MN, USA, and MB, Canada). Selenium concentrations (range, 3.73-52.29 microg/g dry wt) were positively correlated with lipid reserves (F1,73 = 22.69, p < 0.001, type III partial r2 = 0.24), whereas cadmium was negatively correlated with lipid reserves (F1,73 = 6.92, p = 0.010, type III partial r2 = 0.09). The observed relationship between cadmium and lipid reserves may be cause for concern, because lipid reserves of females declined by 55 g (47%), on average, within the range of observed cadmium concentrations (0.23-7.24 microg/g dry wt), despite the relatively low cadmium concentrations detected. Mean cadmium concentrations were higher in Minnesota (1.23 microg/g dry wt) and Manitoba (1.11 microg/g dry wt) than in Louisiana (0.80 microg/g dry wt) and Illinois (0.69 microg/g dry wt). However, mean cadmium concentrations predict lipid reserves of females to be only 11 g lower, on average, in Minnesota than in Illinois. Previous research documented that lipid reserves were 100 g lower in Minnesota than in Illinois; consequently, cadmium is unlikely to be the sole cause for decreases in lipid reserves of females during late-spring migration.

Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats, Alaska

Abstract: Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands &gt;10 ha, small wetlands &lt;10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood‐rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.

Contaminants in Lesser and Greater Scaup Staging on the Lower Great Lakes

The decrease and subsequent lack of recovery of the North American scaup population has increased concerns about contaminants acquired during migration. We collected 189 fall- and spring-migrant lesser (Aythya affinis) and greater scaup (A. marila) on the lower Great Lakes (LGL) to determine if organic contaminants and trace elements in scaup livers were increased and to evaluate sources of variation in selenium (Se) burdens. We found that all organic contaminants were below toxic levels. Of 18 trace elements, only Se was detected at increased (>10-ppm dry-mass) levels. Se in lesser scaup increased but remained constant in greater scaup throughout fall; levels were increased in 14% of lesser scaup and 46% of greater scaup. During spring, Se increased in lesser scaup but decreased slightly in greater scaup; levels were increased in 75% of lesser scaup and 93% of greater scaup. We suggest that Se may be problematic for some breeding female scaup after departing the LGL, but more research is needed to determine the extent to which it affects scaup demographics.

CONTAMINANTS IN LESSER SCAUP EGGS AND BLOOD FROM YUKON FLATS NATIONAL WILDLIFE REFUGE, ALASKA

Abstract Documented declines in Lesser Scaup (Aythya affinis) populations may be caused by several factors, including reduced reproductive success or survival from exposure to environmental contaminants during winter, migration, or breeding. We evaluated organochlorines and inorganic elements in Lesser Scaup blood (n = 14) and eggs (n = 10) from a breeding area in the relatively pristine Yukon Flats National Wildlife Refuge in interior Alaska. Most contaminants were not at concentrations of concern. Lead was detected in only four blood samples, with an average when detected (0.29 mg kg−1 wet weight [ww]) slightly above background levels (0.20 mg kg−1 ww). Our study area had little or no hunting, but since lead exposure is correlated with hunting pressure, lead should be evaluated in other Lesser Scaup breeding areas. Strontium in eggs (mean = 10.90 mg kg−1 dry weight [dw]) was significantly negatively correlated with eggshell thickness. Eggshell thickness was also 18% lower than in museum specimens,...

Effects of Dietary Selenium on Reproduction and Body Mass of Captive Lesser Scaup

Effects of Dietary Selenium on Reproduction and Body Mass of Captive Lesser Scaup

Body Mass of Lesser Scaup during Fall and Winter in the Mississippi Flyway

The combined continental breeding population of greater and lesser scaup (Aythya marila and A. affinis, respectively) in North America has declined markedly since the mid-1980s (Afton and Anderson 2001). Annual breeding population estimates have been consistently below the North American Waterfowl Management Plan (NAWMP) goal of 6.3 million scaup (United States Fish and Wildlife Service and Canadian Wildlife Service 1986), and the 2005 estimate was 46% below the NAWMP goal and the lowest on record (Wilkins et al. 2005). Afton and Anderson (2001) reported the overall decline in scaup may be driven primarily by reductions in the lesser scaup population. Multiple hypotheses have been posed to address the scaup population decline, which may be influenced by factors operating throughout the annual cycle and range of scaup (Austin et al. 2000, Afton and Anderson 2001). Anteau and Afton (2004) evaluated the spring condition hypothesis and reported nutrient reserves of female lesser scaup at spring stopover areas in the upper Mississippi Flyway and breeding areas in Manitoba, Canada, were lower in 2000 and 2001 than in the 1980s and reported that these nutrient reserves may impact female survival, breeding propensity, and reproductive success. However, body mass dynamics of fall migrating and wintering scaup have not been studied since the 1980s and early 1990s in the Mississippi Flyway, and investigations of body mass and nutrient reserves of lesser scaup are needed throughout the annual cycle and range of the species (Austin et al. 2000). Fall and winter body condition influences survival, physiological and behavioral events, and subsequent reproduction of waterfowl (Dubovsky and Kaminski 1994, Barboza and Jorde 2002). Nutrient reserves acquired from foods consumed on wintering and migrational areas can influence breeding propensity and reproductive performance of geese, some ducks, and other migratory birds (Ankney and MacInnes 1978, Alisauskas and Ankney 1992, Norris 2005), including lesser scaup that use lipids acquired during winter, spring migration, or on breeding areas for clutch formation (Esler et al. 2001). We collected lesser scaup during fall 1999–2000 and winter 2000–2001 from Manitoba, Canada, southward within the Mississippi Flyway to Louisiana, USA. Our objectives were to 1) estimate body mass of lesser scaup and analyze sex-specific variation in mass in relation to location of scaup collection, age, body morphometrics, and date of collection, and 2) compare our contemporary estimates of scaup mass to those from previous studies conducted at similar locations.

Lesser Scaup Winter Foraging and Nutrient Reserve Acquisition in East-Central Florida

Lesser scaup (Aythya affinis) populations have been declining since the late 1970s. One of the explanations to account for this decline, the spring-condition hypothesis (SCH), is based on the premise that scaup are limited by their ability to acquire or maintain nutrient reserves during migration to the breeding grounds, leading to an impairment of their reproductive potential. Available evidence suggests that endogenous reserves required for reproduction are obtained at a later stage of migration or after arrival at the breeding grounds, not wintering sites. However, only one study has addressed body-condition levels on a southern wintering site in the last decade, with results limited to the wintering grounds on the Mississippi Flyway. We documented foraging behavior, nutrient levels, and body mass of lesser scaup in east-central Florida, USA, where 62% of the Atlantic Flyway population overwinters, during the winters of 2002 and 2003. Diurnal foraging did not increase seasonally. Nocturnal foraging increased seasonally by 76% or 43 minutes per night in females and by 478% or 1.9 hours per night in males. Measures of body condition did not change seasonally during 2002 for either sex. Between early and later winter in 2003 corrected body mass (CBM) and lipid reserves of male scaup increased 77 g and 39 g, respectively. Our results suggest that lesser scaup maintain or may slightly improve their physiological condition in east-central Florida during winter. Lower body mass and differences in nutrient levels in east-central Florida, compared to a wintering site in Louisiana, likely stem from geographic variation and lower thermal requirements associated with the warmer Florida environment. Lesser scaup depart Florida with sufficient reserves to initiate spring migration, but they maximize nutrient reserves used during reproduction elsewhere during migration or on the breeding grounds. These results suggest that maintaining the ecological integrity of this wintering ground is critical in minimizing winter mortality and preventing it from becoming an ancillary factor in current declines. Future research should address understanding survival rates during spring migration and at critical staging areas to provide new insight into the ramifications of scaup leaving wintering habitats such as MINWR with lower body condition than at other wintering sites in other flyways.

Shot Ingestion in Scaup on the Lower Great Lakes After Nontoxic Shot Regulations in Canada

Use of lead shot for waterfowl hunting was banned in the United States in 1991 to reduce the incidence of lead toxicosis in waterfowl. In 1999 Canada implemented a similar ban. The lower Great Lakes (LGL) are important migratory areas for greater (Aythya marila) and lesser scaup (A. affinis). Prior to the implementation of the Canadian ban, 11% and 8% of greater and lesser scaup harvested in the LGL, respectively, had ingested lead shot. We collected greater and lesser scaup on the Canadian side of lakes Erie, Ontario, and St. Clair during autumn 1999 and spring 2000 to determine if lead shot ingestion declined 1 year after the ban in Canada. There were no intraspecific (lake, season, sex, or age) or interspecific differences in proportion of birds containing ingested shot. Overall, only 0.6% of birds (n = 4 of 722) contained lead shot and only 3.1% contained nontoxic shot. The low frequency of toxic relative to nontoxic shot ingestion suggests that shot may quickly become inaccessible to scaup on lacustrine areas of the Great Lakes. Thus, the risk of lead toxicosis to scaup migrating through the LGL appears low at this time. Pre- and postban differences in overall ingestion frequencies (8–11% vs. 3.7%) suggests that preban numbers may have been biased (elevated) because lead shot ingestion can increase harvest susceptibility. However, recent scaup dietary shifts may also have contributed to overall declines in shot consumption. Low postban lead shot ingestion may also be indicative of high hunter compliance with nontoxic shot regulations in Canada.

Diets of Lesser and Greater Scaup During Autumn and Spring on the Lower Great Lakes

We examined diets of lesser scaup (Aythya affinis) and greater scaup (A. marila) during autumn 1999 and spring 2000 at 3 major stopover sites on lakes Erie, Ontario, and St. Clair in southern Ontario, Canada. Overall dietary composition did not differ between sexes in lesser or greater scaup. We also did not detect interspecific or sex-related differences in average size of zebra mussels (Dreissena polymorpha) consumed by scaup, but both species ate slightly larger zebra mussels during spring, as compared with autumn. Dietary intake of lesser scaup differed between seasons and among stopover sites. Lesser scaup generally ate more zebra mussels during spring and more gastropods and plants during autumn. Lesser scaup at Lake Ontario, Lake Erie, and Lake St. Clair, respectively, consumed more zebra mussels, nonmollusk animal matter (crustaceans and insects), and plant matter than did conspecifics at the other 2 locations. Greater scaup diets differed depending on both season and stopover site. At Lake Ontario greater scaup diets contained more zebra mussels but fewer gastropods during spring as compared with autumn, but there were no seasonal differences in consumption of those 2 food items at Lake Erie. Greater scaup at both Lake Ontario and Lake Erie did not show seasonal differences in consumption of plant matter, but autumn-staging birds at Lake Erie contained more plant matter than did autumn-staging birds at Lake Ontario. Interspecific comparisons of dietary intake of scaup staging at lakes Erie and Ontario showed that greater scaup generally ate more gastropods and plant matter than did lesser scaup, whereas lesser scaup consumed more zebra mussels than did greater scaup. Overall, our study showed that zebra mussels, gastropods, and submerged aquatic plants all currently are important foods during both autumn and spring for lesser and greater scaup staging on the lower Great Lakes (LGL). Consumption of zebra mussels by scaup is of particular concern because of the hypothesized link between scaup foraging ecology, zebra mussels, and elevated selenium burdens documented recently in scaup staging on the LGL. Thus, our findings that both scaup species generally ate more and larger zebra mussels during spring illustrates the need for further investigation into contaminant acquisition and burdens in wintering, staging, and breeding scaup, particularly those using, or originating from, the LGL region.

Evaluating cytochrome P450 in lesser scaup (Aythya affinis) and tree swallow (Tachycineta bicolor) by monooxygenase activity and immunohistochemistry: Possible nonlethal assessment by skin immunohistochemistry

Six-month-old lesser scaup (Aythya affinis) and nestling tree swallows (Tachycineta bicolor) were injected intraperitoneally with beta-naphthoflavone (BNF) in corn oil or in vehicle alone. Liver samples were taken and stored at -80 degrees C until microsome preparation and monooxygenase assay. Skin samples were placed in buffered formalin for subsequent immunohistochemical (IHC) analysis for cytochrome P4501A (CYP1A). Lesser scaup treated with BNF at 20 or 100 mg/kg body weight showed approximately 6- to 18-fold increases in four monooxygenases (benzyloxyresorufin-O-dealkylase, ethoxyresorufin-O-dealkylase, methoxyresorufin-O-dealkylase, and pentoxyresorufin-O-dealkylase). No IHC response was observed for CYP1A in the skin of vehicle-injected ducks, whereas in the skin from BNF-treated ducks, the positive IHC response was of similar magnitude for both dose levels of BNF. Tree swallows injected with BNF at 100 mg/kg, but not at 20 mg/kg, showed significant increases (approximately fivefold) in hepatic microsomal O-dealkylase activities. Cytochrome P4501A was undetectable by IHC response in skin from corn oil-treated swallows, but positive IHC responses were observed in the skin of one of five swallows at 20 mg/kg and four of five swallows at 100 mg/kg. Although these data do not allow construction of significant dose-response curves, the IHC responses for CYP1A in skin support the possible use of this nonlethal approach for biomonitoring contaminant exposure of birds. In addition, the CYP1A signal observed at the bases of emerging feathers suggest that these might provide less invasive sampling sites for IHC analysis of CYP1A.

Geographic variation in the isotopic (δD, δ13C, δ15N, δ34S) composition of feathers and claws from lesser scaup and northern pintail: implications for studies of migratory connectivity

Stable hydrogen isotope (δD) measurements of bird feathers can reveal approximate North American latitudes where feathers were grown by linking feather δD values to well-defined geographic patterns in δD values in growing-season precipitation. In waterfowl, this approach may require caution because wetlands are potentially “disconnected” from predictable isotopic patterns in precipitation waters. Stable carbon (δ13C), nitrogen (δ15N), and sulphur (δ34S) isotope values of avian tissues may show geographic structure but can be complicated by land use. We analyzed claws of wintering adult northern pintails (Anas acuta L., 1758) from California and Texas, and feathers and claws of lesser scaup ( Aythya affinis (Eyton, 1838)) ducklings from northwestern North America, to determine geographic variation in δD, δ13C, δ15N, and δ34S values. Wintering pintails from Texas and California were distinguished with claw δD and δ15N values. In scaup, feather δD values differed among biomes and were positively associated with latitude; geographic variation in other isotopes was less pronounced. The δD values in feathers and claws of individual scaup ducklings were correlated. A positive relationship between scaup feather δD values and δD values in growing-season precipitation was similar to results reported for songbirds. Thus, δD values in waterfowl feathers can provide new knowledge about natal origins and moulting sites.

Effects of water quality on habitat use by lesser scaup (Aythya affinis) broods in the boreal Northwest Territories, Canada

Effects of water quality on habitat use by lesser scaup (Aythya affinis) broods in the boreal Northwest Territories, Canada

Spatial structure of a diving duck (Aythya, Oxyura) guild: how does habitat structure and competition influence diving duck habitat use within northern prairie wetlands?

What circumstances allow the coexistence of similar species is a common but complex question in community ecology. It is often assumed that sympatric species within the same guild must employ some mechanism of niche diversification to coexist. Diving duck (Anatidae: Aythya Boie, 1822 and Oxyura Bonaparte, 1828) competition is poorly understood and current evidence of coexistence mechanisms is contradictory. In the spring and summer of 2001 and 2002, we tested whether diving ducks foraging within prairie potholes segregate by depth to avoid competition. We sought to explain any segregation by sampling sediment particle size, compactness, and organic content; submergent vegetation; and benthic invertebrate densities in the foraging locations of each species. Our study was conducted at the wetland scale in southwestern Manitoba, Canada. We found that Redheads ( Aythya americana (Eyton, 1838)), Ruddy Ducks ( Oxyura jamaicensis (J.F. Gmelin, 1789)), Canvasbacks ( Aythya valisineria (Wilson, 1814)), and Ring-necked Ducks ( Aythya collaris (Donovan, 1809)) foraged most often at shallow depths (50–100 cm), while Lesser Scaups ( Aythya affinis (Eyton, 1838)) foraged at shallow to intermediate depths (50–150 cm). Thus, most divers did not segregate by depth. These results conflict with an earlier study that reported diving ducks segregated by depth to avoid competition. Diving ducks likely forage where prey abundance is greatest relative to the cost of diving to obtain that prey.

Lesser Scaup Spring Nutrient Reserve Dynamics on the Lower Great Lakes

The North American lesser scaup (Aythya affinis) population has declined since the mid-1980s. The acquisition of nutrient reserves during spring migration may play a role in explaining that trend. We studied nutrient-reserve dynamics of lesser scaup collected during spring at 3 major stopover sites and assessed whether reserves of birds on the lower Great Lakes (LGL) differed from those at other staging (or breeding) areas. At lakes Ontario and St. Clair, males had larger fat reserves than females, but no other substantial sex-related differences were observed in fat, protein, or mineral reserve levels of lesser scaup. Protein in males and mineral reserves of both sexes at lakes Erie and St. Clair did not change throughout spring. Male fat reserves remained constant at Lake Erie and increased at Lake St. Clair, whereas female fat and protein reserves increased at both stopover sites. Patterns of fat and protein dynamics in males partly may be due to energetic costs of courtship and pair-bond maintenance. However, maintenance and accumulation of fat reserves in both sexes while on the LGL is important for impending migration and subsequent reproduction. Female lesser scaup staging on the LGL had fat reserves comparable to, or slightly higher than, those reported in other studies of northern spring-staging and breeding birds. Fat reserves of LGL females, however, were much lower than those reported for birds at another midlatitude stopover site. These comparisons suggest that events occurring on Atlantic Flyway wintering areas or LGL staging areas are potential factors contributing to nutrient-reserve limitation and possibly to observed declines in scaup numbers in North America.