Comparative reproductive energetics and selenium ecotoxicology in three boreal-breeding waterfowl species

Environmental conditions on wintering or spring-staging areas may influence subsequent reproductive performance in migratory birds. These cross-seasonal effects may result from habitat loss and degradation (e.g., via contamination) which in turn reduce reproductive success, particularly in waterfowl that use stored nutrients for reproduction. North American lesser scaup (Aythya affinis) and white-winger scoter (Melanitta fusca) numbers have declined over the past 20 years, particularly in the boreal forest, and remain well below conservation goals, whereas ring-necked duck (A. collaris) numbers have increased. Environmental changes on scaup and scoter wintering and staging areas have raised concern about possible cross-seasonal effects on birds arriving on breeding grounds. The spring condition hypothesis (SCH) purports that many female scaup fail to acquire sufficient nutrients in late winter and spring, causing a decrease in breeding propensity and productivity. The contaminant hypothesis proposes that increased exposure to contaminants (particularly selenium [Se]) on wintering and staging areas has decreased scaup productivity. Accordingly, I compared body condition and studied Se concentrations in scaup, scoters and ringnecks to test the condition and contaminant hypotheses. Scaup had similar body condition to ringnecks, and had similar body mass compared to scaup collected near Yellowknife, NT, in 1968-70. There was no relationship between scaup and ringneck nutrient levels and claw tip carbon, nitrogen or hydrogen isotope values, suggesting that arrival body condition likely was not related to location or diet several months prior. Instead, scaup and ringnecks nutrient levels may be more affected by feeding or habitat conditions on or near the breeding grounds. Scaup had slightly higher liver Se concentrations than ringnecks, but levels in both species were below recognized harmful threshold concentrations; I found no relationship between Se and breeding propensity, or between Se and somatic lipid or protein stores. Scoters had much higher Se concentrations, yet contrary to predictions, there were positive relationships between Se and both lipid stores and breeding status. Follicle [Se] in scaup was below threshold concentrations; despite high liver Se in scoters, egg and follicle levels also were well below threshold concentrations. Using both body composition analysis and stable-isotope analysis I determined that scoters derive egg protein from their breeding ground diet, which likely prevents Se deposition from somatic protein to eggs, and egg lipids are apparently derived from somatic tissues. In all three species, liver Se concentrations were significantly correlated with claw tip ä15N. As the claw tip likely represents assimilated diet from 2-5 months prior to sampling, this correlation suggests that Se in these boreal breeding species is carried over from wintering and staging areas. Overall, results did not support either the spring condition or contaminant hypotheses. Scaup and scoters are late-nesting species, with highest pair densities occurring at the northern extent of their range. Maximum ring-neck pair densities occur at more southern latitudes. Ring-necks also nest earlier and appear to be more flexible in timing of nest initiation. Therefore, it is possible that due to climate change, early spring conditions alter the optimal timing of nest initiation to the detriment of late-nesting species such as scaup and scoters, and favour earlier nesters like ringnecks. Further research into this mismatch hypothesis is warranted

Eye Colour, Aging, and Decoy Trap Bias in Lesser Scaup, Aythya affinis

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

Cross-Seasonal Association Between Winter Trophic Status and Breeding Ground Selenium Levels in Boreal White-Winged Scoters

The effect of cross-seasonal interactions on reproduction and fitness in migratory species is of increasing interest to ecologists, particularly because of the conservation implications of habitat change. Variation in contaminant levels that can affect reproduction in migratory species may reflect differing exposure across seasons. We examined the relationship between concentrations of liver selenium, a known teratogen, and winter trophic level in breeding White-winged Scoters (Melanitta fusca) using claw δ15N values as an index of winter trophic level. Claw δ15N was a significant predictor of variation in breeding ground selenium levels (r = 0.32), and liver selenium increased by approximately 12 ± 5 SE μgâg-1 with one trophic level increase in δ15N (Î"3). This relationship demonstrates that contaminant exposure from wintering or staging areas can result in higher levels in birds on breeding grounds, where some contaminants are more likely to have impacts

Supplement 1. Annotated INLA code for the model with snow cover extent from 1967–2010.

<h2>File List</h2><div> <p><a href="INLA_code.R">INLA_code.R</a> (MD5: 68c372169a851d7616d30172ce203f50)</p> <p><a href="ss_model_inla.csv">ss_model_inla.csv</a> (MD5: 3b3bf472211df425134b22e33dbac549)</p> </div><h2>Description</h2><div> <p>INLA_code.R is an R script file to analyze scaup pair abundance using a Gompertz state-space model containing a covariate for snow cover extent. This script assumes that the INLA package has been downloaded from <a href="http://www.r-inla.org">http://www.r-inla.org</a>. The data set (ss_model_inla.csv) should be in the working directory when running this code.</p> <p>ss_model_inla.csv is a comma-separated text file containing the scaup dataset. Column definitions are:</p> <ol> <li>y: counts from each stratum in each year from BPOP aerial survey</li> <li>stratum: each stratum number, adjusted for analysis in INLA, where ‘1’ = Stratum 13 as defined by the BPOP survey, ‘2’ = Stratum 14, ‘3’ = Stratum 15, ‘4’ = Stratum 16, ‘5’ = Stratum 17, and ‘6’ = Stratum 18</li> <li>year: year since beginning of survey (1955)</li> <li>stand.snow: standardized covariate for snow cover extent</li> <li>N: number of segments flown in each stratum each year</li> </ol> </div

Appendix A. Model rankings of the independent analyses of climate (both 1958–2010 and 1968–2010 separately), predation, and density dependence.

Model rankings of the independent analyses of climate (both 1958–2010 and 1968–2010 separately), predation, and density dependence