Eider Research Articles

River influence on mercury bioaccumulation in the coastal food web of Eeyou Istchee, James Bay, Canada

Spatial patterns of bioaccumulated mercury were evaluated in coastal marine food webs of east Hudson Bay and east James Bay in the boreal subarctic of Canada. Two marine species, blue mussels ( Mytilus edulis) and common eider ducks ( Somateria mollissima) that consume mussels, were collected by a regional community-based monitoring network established in five communities. Stable isotope tracers (carbon, nitrogen, sulfur, and mercury) were measured to evaluate environmental drivers of mercury spatial patterns. Mercury concentrations of blue mussels and common eiders were twofold and fivefold higher, respectively, on the James Bay coast near the community of Chisasibi compared to sites in east Hudson Bay. Liver and muscle mercury concentrations of eiders from James Bay are among the highest values reported for the circumpolar subarctic and Arctic. Multiple lines of evidence (mercury spatial patterns, crustal elements in blue mussels, and mercury isotope values of common eiders) suggest elevated mercury in the coastal food web of east James Bay may be due to mercury loading from the La Grande River, which drains one of the largest hydroelectric developments in the world. These findings highlight the importance of further research on environmental processes linking large rivers to mercury bioaccumulation in northern coastal food webs.

Collaboration between local Indigenous and visiting non‐Indigenous researchers: Practical challenges and insights from a long‐term environmental monitoring program in the Canadian Arctic

Abstract There is a growing appreciation for the value of collaborative research projects involving local Indigenous and visiting non‐Indigenous researchers. Examples of such partnerships are now numerous and diverse, and best practices and respectful approaches have been well presented, including the five priorities of the National Inuit Strategy on Research (NISR) defined by Inuit Tapiriit Kanatami in Canada. However, the application of best practices remains challenging, and examples of ‘on‐the‐ground’ implementation remain scarce in the literature. We present a practical case study in which scientists from the Federal Department of Environment and Climate Change Canada and Inuit have co‐delivered a multidecade‐long monitoring program of nesting common eider ducks Somateria mollissima in the Arctic. We review our experience as southern‐based government researchers in this collaboration. We reflect on successes and, more importantly, on the practical challenges that prevent the full implementation of best practices in our program. First, we highlight challenges to co‐designing a data collection protocol that combines both Indigenous and Western scientific methods. We show how combining the strengths of Inuit Knowledge and rigorous random sampling design has led to a more powerful approach to eider population monitoring. Second, we review how the federal government's administrative approaches are poorly suited for employing seasonal Indigenous workers living in remote communities, particularly in Canada. We argue that to deliver respectful employment and payment practices, the financial and hiring administration of collaborative projects must be based at the community level. Finally, we show how sociocultural factors have made it challenging to ensure the safety of all field workers consistently. To increase their perceived value and uptake, we suggest that safety guidelines must be co‐designed by visiting researchers and local partners for each project to ensure that they are appropriate to the local culture, field conditions, and the nature of the fieldwork. Based on our experience, we draw attention to gaps that still exist between the best practices of collaborative research and factors that hamper their practical implementation. We invite other research teams to do the same so that, collectively, we can improve collaborative approaches nationally and internationally.

A colonial-nesting seabird shows no heart-rate response to drone-based population surveys

Aerial drones are increasingly being used as tools for ecological research and wildlife monitoring in hard-to-access study systems, such as in studies of colonial-nesting birds. Despite their many advantages over traditional survey methods, there remains concerns about possible disturbance effects that standard drone survey protocols may have on bird colonies. There is a particular gap in the study of their influence on physiological measures of stress. We measured heart rates of incubating female common eider ducks (Somateria mollissima) to determine whether our drone-based population survey affected them. To do so, we used heart-rate recorders placed in nests to quantify their heart rate in response to a quadcopter drone flying transects 30 m above the nesting colony. Eider heart rate did not change from baseline (measured in the absence of drone survey flights) by a drone flying at a fixed altitude and varying horizontal distances from the bird. Our findings suggest that carefully planned drone-based surveys of focal species have the potential to be carried out without causing physiological impacts among colonial-nesting eiders.

Disease surveillance in England and Wales, June 2022.

Disease surveillance in England and Wales, June 2022.

Egg-laying increases body temperature to an annual maximum in a wild bird

Most birds, unlike reptiles, lay eggs successively to form a full clutch. During egg-laying, birds are highly secretive and prone to disturbance and predation. Using multisensor data loggers, we show that average daily body temperature during egg-laying is significantly increased (1 °C) in wild eider ducks (Somateria mollissima). Strikingly, this increase corresponds to the annual maximum body temperature (40.7 °C), representing a severe annual thermogenic challenge. This egg-laying-induced rise in body temperature may prove to be a common feature of wild birds and could be caused by habitat-related thermoregulatory adjustments and hormonal modulation of reproduction. We conclude our findings with new perspectives of the benefits of high body temperature associated with egg-laying of birds and the potential effect of heat stress that may occur with the future advent of heatwaves.

Environmental and life-history factors influence inter-colony multidimensional niche metrics of a breeding Arctic marine bird

Human industrialization has resulted in rapid climate change, leading to wide-scale environmental shifts. These shifts can modify food web dynamics by altering the abundance and distribution of primary producers (ice algae and phytoplankton), as well as animals at higher trophic levels. Methylmercury (MeHg) is a neuro-endocrine disrupting compound which biomagnifies in animals as a function of prey choice, and as such bioavailability is affected by altered food web dynamics and adds an important risk-based dimension in studies of foraging ecology. Multidimensional niche dynamics (MDND; δ13C, δ15N, THg; total mercury) were determined among breeding common eider (Somateria mollissima) ducks sampled from 10 breeding colonies distributed across the circumpolar Arctic and subarctic. Results showed high variation in MDND among colonies as indicated by niche size and ranges in δ13C, δ15N and THg values in relation to spatial differences in primary production inferred from sea-ice presence and colony migratory status. Colonies with higher sea-ice cover during the pre-incubation period had higher median colony THg, δ15N, and δ13C. Individuals at migratory colonies had relatively higher THg and δ15N, and lower δ13C, suggesting a higher trophic position and a greater reliance on phytoplankton-based prey. It was concluded that variation in MDND exists among eider colonies which influenced individual blood THg concentrations. Further exploration of spatial ecotoxicology and MDND at each individual site is important to examine the relationships between anthropogenic activities, foraging behaviour, and the related risks of contaminant exposure at even low, sub-lethal concentrations that may contribute to deleterious effects on population stability over time. Overall, multidimensional niche analysis that incorporates multiple isotopic and contaminant metrics could help identify those populations at risk to rapidly altered food web dynamics.

Seaduck engineers in the Arctic Archipelago: nesting eiders deliver marine nutrients and transform the chemistry of island soils, plants, and ponds

Seabirds are thought to provide ecological services such as the movement of nutrients between marine and terrestrial ecosystems, which may be especially critical to productivity and diversity in nutrient-poor environments. Most Arctic ecosystems are unaffected by local human impacts and are naturally nutrient poor and especially sensitive to warming. Here, we assessed the effects of nesting common eider ducks (Somateria mollissima) on soil, vegetation, and pond sediments on island archipelagoes in Hudson Strait between Nunavut and Québec, Canada. Soil, moss, and pond sediments were significantly higher in nitrogen on islands with large numbers of nesting eiders compared to sites with no nesting birds. The highest concentrations of nitrogen in soils and moss occurred at the margins of ponds on eider islands, which correspond to the areas of highest eider use. δ15N and δ34S values in soils, moss, and sediments indicated substantial marine-derived organic matter inputs at the higher nutrient sites. We propose that by foraging on coastal marine benthic invertebrates and returning to islands to nest, eider ducks bio-transport and concentrate marine-derived nutrients to their colony islands, fertilizing Arctic island ecosystems in the process. As common eiders nest on thousands of low to mid-latitude islands throughout the circumpolar Arctic, these nutrient inputs likely dramatically affect biota and ecosystem functioning throughout the tundra biome.

A Surgery of a Star by Margarita Serafimova

BOOKS IN REVIEW the inevitable change of seasons and the elementary techniques of rendering raw nature hospitable. Jacobsen depicts the harshness in the encounters between people and their surroundings as well as the one between people themselves by strictly undernarrating the emotional dimension of his taciturn characters while sharing their rich knowledge of sustaining themselves in great detail. As a result, we learn more about their ways of gutting cod or selling the precious feathers of eider ducks than about the inner lives of men and women who don’t dwell in the pain inflicted on them. This is not to suggest that the tight economy of Jacobsen’s art of storytelling would deny his readers a suspenseful line of events. A plot is slowly set into motion when Ingrid clandestinely offers a soldier of unknown colors refuge in her home and in her heart. Washed ashore on Ingrid’s poverty-stricken island from a troop carrier sunk by British planes, the survival of the badly injured man needs to be hidden from the German occupying forces. The readers, too, will get to learn only specks of his identity: Ingrid “asked whether he was a Russian and he said Da, but only after she had repeated the question three times. She asked if he was a soldier and he answered yes and no, she had never felt more attractive , and she stopped asking questions.” Jacobsen does deny us, however, the illusion that there can be happiness in the time of collaboration and war, when knowing as little as possible appears to be as tantamount to survival as sharing even less. The brief moment in which Ingrid and her torn-up soldier “lay in the North Chamber like husband and wife” is crushed by the pitiless realities of brute force that threaten to render Ingrid helpless, if not lifeless altogether. After a vicious assault that robs Ingrid of her memory of the attack on her, she needs to set out to rebuild her sense of self as a member of a community in which it is at times impossible to tell friend from foe. Bodily harmed, she is also emotionally scarred as she and her readers are trying to reconstruct the circumstances and the motive of the assault on her. Despite the inability of the protagonist to articulate what she is experiencing and her lack of introspection, White Shadow is a powerful psychological novel precisely because it doesn’t bother to give a voice to Ingrid. Not knowing “the difference between what has to be remembered and what forgotten,” Ingrid emerges as a cipher for a people ravaged by an enemy who has taken more than just their land and homes. Over the course of the novel, it becomes clear that White Shadow is a powerful psychological novel about a people’s devastation by the war and their subsequent attempts at reestablishing order out of persecution; loss of property, memory, and honor; of poverty; and of nameless crimes. The narrowly constricted world of Ingrid’s tiny island—which in the first part of the Ingrid Barrøy trilogy could still be told as the story of a family—has been shattered and is replaced by the story of the displaced “Finns and Lapps,” no longer “kept separate from the Norwegians,” as they join Ingrid in rebuilding her home. Don Bartlett and Don Shaw offer a translation that conveys the book’s regionalisms (“Ingrid told him to clear off, an’ don’t show tha face hier again”) as well as the bone-dry cadence of a prose whose sentences tend to be anticlimactic—just like the lives that they tell. Thomas Nolden Wellesley College Margarita Serafimova A Surgery of a Star Trans. by the author. Sonoma County, Calif. Staring Problem Press. 2020. 48 pages. My eyes goldened. / You are mirrored in the surface / of my internal organs. –Margarita Serafimova, “My eyes goldened” ONE BLINK. A snapshot taken. Time frozen in a few lines. Margarita Serafimova’s poetry captures a moment in time as perceived by the poet, revealing her bodily and mental experiences to readers in words that appear simple in their choice but create complex, thought-provoking scenes from that simplicity...

Technique to study poop offers a snapshot of diets, ecosystems, and climate

Hundreds of thousands of eider ducks once nested on the remote, rocky beaches of the Canadian Arctic. But sometime late in the 19th century, eiders began to disappear. Inuit oral traditions recall declines well before most scientific seabird censuses came so far north in the 1970s, says paleolimnologist Jules Blais at the University of Ottawa in Canada. To understand exactly when and why past duck populations crashed, Blais uses an emerging tool: stable isotope analysis of duck poop. The story of Baffin Island’s eider ducks is told in stable isotopes of duck poop stored in years of sediment. Researchers across fields are now using fecal isotope analysis to answer a range of research questions. Image credit: Grant Gilchrist (Environment and Climate Change Canada, Ottawa, Canada). Stable isotope analysis itself is nothing new. An established technique in several fields, it uses isotopes to trace physical and biological processes. For example, because isotopes—atoms of an element that vary in their number of neutrons—have slightly different weights, they exist in different kinds of food in distinctive ratios and therefore move into body tissues in distinctive ratios. These ratios are widely used to work backward from bone or hair to infer the diets of animals or ancient humans. But fecal matter hasn’t generally been a go-to material for this kind of isotope research—until recently. Fecal stable isotope analysis is catching on in ecology, paleoecology, and paleoclimatology in part because samples are easy to collect and offer a quick snapshot of an animal’s diet. Some researchers are applying stable isotope analysis to poop to study modern and ancient diets, whereas others use it to reconstruct past ecology, climates, and environments, says paleoecologist Rachel Reid at the Virginia Polytechnic Institute and State University in Blacksburg. In the eider duck case, Blais analyzed the ratio of stable …

Numerical modeling of submerged mussel longlines with protective sleeves

Farmers growing mussels in offshore environments have turned to submerged longline farming as a relatively safe, reliable and profitable way to produce mussels in the exposed ocean environment. However, variations in the environmental conditions (strong currents and storms) and potential presence of predator species (e.g. eider ducks) require robust engineering approaches to design longline mussel farms and their components.This paper describes application of a mechanistic fluid-structure interaction modeling software Hydro-FE to predict the dynamic response of several mooring/longline/dropper configurations subjected to typical and extreme environmental conditions of a North Atlantic mussel farming site. Hydro-FE is a software tool that expands and modernizes the approach previously implemented in the finite element program Aqua-FE developed at the University of New Hampshire to analyze flexible structures in marine environment. The numerical model takes into account smooth variation of the hydrodynamic forces around the free surface (continuous partial submergence), Reynolds number dependence of drag coefficients of mooring lines and includes contributions of predator-protection sleeves to the overall mechanical response of mussel droppers. The simulations provide estimates of anchor forces, mooring line tensions, and time-series data on the motion of the droppers. This information can be used in the design of mussel longlines to prevent anchor failure, rope breakage, line entanglement and mussel fall-off.

Anti-parasite treatment results in decreased estimated survival with increasing lead (Pb) levels in the common eider Somateria mollissima.

Field experiments where parasites are removed through treatment and contaminant levels in host tissues are recorded can provide insight into the combined effects of parasitism and contaminants in wild populations. In 2013 and 2014, we treated northern common eider ducks (Somateria mollissima) arriving at a breeding colony with either a broad-spectrum antihelminthic (PANACUR®) or distilled water, and measured their blood lead (Pb) levels. Breeding propensity and clutch sizes were inversely related to Pb in both treatment groups. In comparison, a negative effect of Pb on resight probability the following year was observed only in the anti-parasitic treatment (APT) group. These contrasting patterns suggest a long-term benefit to survival of intestinal parasitism in eiders experiencing Pb exposure. The arrival date of hens explained some, but not all, of the effects of Pb. We weigh the merits of different hypotheses in explaining our results, including protective bioaccumulation of Pb by parasites, condition-linked thresholds to costly reproduction and the direct effects of APT on eider health. We conclude that variation in helminth parasitism influences survival in this migratory bird in counterintuitive ways.

Allocation of body reserves during winter in eider Somateria mollissima as preparation for spring migration and reproduction

Capital breeders, such as the eider duck Somateria mollissima, accumulate resources before the start of breeding. Eiders preferentially feed on blue mussels Mytilus edulis to build up body condition during winter. We explored how body condition and gizzard mass of wintering eiders relate to mussel quality and quantity, winter climate and body condition of females at the breeding grounds. Body condition during winter (defined as scaled body mass index) of eiders increased during winter and the magnitude of the effect depended on age and mussel quality. Gizzard mass of eiders increased during winter with effects of mussel quality, mussel stocks and sex. Body condition in winter of adult females increased from the first half of January to the second half of February on average by 1.5%, equal to c. 96 g. During the same period gizzard mass of adult females increased by 12.2%, i.e., a nearly ten-fold increase compared to that observed in body condition in winter. Body condition of females at the breeding grounds in Finland (defined as body condition at hatching) was significantly positively correlated with gizzard mass in winter, but not significantly correlated with body condition in winter. Thus, eiders allocate body reserves to increase gizzard mass but less so to increase body condition in winter. This can be considered an adaptive migratory strategy of these eiders, whereby large winter (pre-migratory) gizzards increase food processing capacity, making it possible for eiders to arrive at the breeding grounds with superior body condition and a high reproductive potential.

Sources of variation in endohelminth parasitism of common eiders over-wintering in the Canadian Arctic

Documenting how climate change will affect Arctic ecosystems and food web dynamics requires an understanding of current sources of variation in species distributions, frequency, and abundance. Host–parasite interactions are expected to be altered in the coming decades under warming conditions. However, in many Polar Regions, there is little information describing parasite–host assemblages. We examine how gastrointestinal helminths of northern common eider ducks (Somateria mollissima sedentaria) in the low Arctic vary with host age, sex and sampling year. We found that the prevalence of an acanthocephalan (Profilicollus sp.) varied in eiders with age, sex and year, while a cestode (Microsomacanthus sp.) varied with host sex. Two other species of endohelminths (Lateriporus sp., Corysonoma sp.) were not found to vary with sex, age or sampling year, and another species (Microphallus sp.) did not vary with sex or age. Our results highlight the complexity inherent in Arctic host–parasite assemblages, and the need for more detailed studies to better understand how changing climatic conditions may affect species distributions, frequency or abundance.

Breeding eider ducks strongly influence subarctic coastal pond chemistry

Arctic freshwater ponds are typically pristine and oligotrophic, however seabird biovectors can markedly alter water quality via enrichment with marine-derived nutrients and bioaccumulated metals. These ornithogenic inputs can be the dominant factor structuring aquatic biota and the surrounding island flora. Here, we measured a suite of limnological water chemistry variables and sediment geochemistry from 21 freshwater ponds influenced by Common Eiders (Somateria mollissima) in Hudson Strait, near the northern communities of Cape Dorset (Nunavut) and Ivujivik (Quebec). Nest counts and sedimentary δ15N values were used as proxies of bird abundance. Nutrient-rich guano from the nesting eiders visibly promoted the growth of catchment vegetation. Elevated metal (Al, Cd, Zn), metalloid (Se), and nutrient concentrations (N, P) in the water of eider-affected sites were recorded (Sign test; p = 0.004), but the proximity of many sites to the coast meant that variables related to ocean spray (conductivity, Na+, Mg2+, Cl−, Sr) confounded the effects of birds on pond water chemistry. In contrast, sediment geochemistry appeared to more clearly characterize sites according to the level of eider activity in their catchments by tracking Pb, Cd, N, and P sedimentary concentrations (Sign test; p = 0.02). These results have direct implications for reconstructing historical eider population trends using sediment archives, which is necessary to inform effective conservation management strategies.

Increased male bias in eider ducks can be explained by sex-specific survival of prime-age breeders.

In contrast to theoretical predictions of even adult sex ratios, males are dominating in many bird populations. Such bias among adults may be critical to population growth and viability. Nevertheless, demographic mechanisms for biased adult sex ratios are still poorly understood. Here, we examined potential demographic mechanisms for the recent dramatic shift from a slight female bias among adult eider ducks (Somateria mollissima) to a male bias (about 65% males) in the Baltic Sea, where the species is currently declining. We analysed a nine-year dataset on offspring sex ratio at hatching based on molecularly sexed ducklings of individually known mothers. Moreover, using demographic data from long-term individual-based capture-recapture records, we investigated how sex-specific survival at different ages after fledgling can modify the adult sex ratio. More specifically, we constructed a stochastic two-sex matrix population model and simulated scenarios of different survival probabilities for males and females. We found that sex ratio at hatching was slightly female-biased (52.8%) and therefore unlikely to explain the observed male bias among adult birds. Our stochastic simulations with higher survival for males than for females revealed that despite a slight female bias at hatching, study populations shifted to a male-biased adult sex ratio (> 60% males) in a few decades. This shift was driven by prime reproductive-age individuals (≥5-year-old), with sex-specific survival of younger age classes playing a minor role. Hence, different age classes contributed disproportionally to population dynamics. We argue that an alternative explanation for the observed male dominance among adults–sex-biased dispersal–can be considered redundant and is unlikely, given the ecology of the species. The present study highlights the importance of considering population structure and age-specific vital rates when assessing population dynamics and management targets.

Sustaining ecological and subsistence functions in conservation areas: eider habitat and access by Native hunters along landfast ice

SUMMARYIn the Arctic, rapid climate change has kindled efforts to delineate and project the future of important habitats for marine birds and mammals. These animals are vital to subsistence economies and cultures, so including the needs of both animals and hunters in conservation planning is key to sustaining social-ecological systems. In the northeast Chukchi Sea, a nearshore corridor of open water is a major spring migration route for half a million eider ducks that are hunted along the landfast ice. Zoning areas for industrial activities or conservation should consider both eider habitat and hunter access to those habitats from the variable ice edge. Based on benthic sampling in 2010‒2012, a model of eider foraging energetics and satellite data on ice patterns in April and May 1997‒2011, we mapped the range of positions of the landfast ice edge relative to a given dispersion of habitat suitable for eider feeding. In some sectors, feeding areas were too limited or too far from landfast ice to provide regular hunting access. In other sectors, overlap of the ice edge with eider feeding habitat was quite variable, but often within a consistent geographic range. Areas accessible to hunters were a small fraction of total eider habitat, so areas adequate for conserving eiders would not necessarily include areas that meet the hunters’ needs. These results can inform spatial planning of industrial activities that yield cash income critical to subsistence hunting in less developed locations. Our study provides an approach for mapping ‘subsistence conservation areas’ throughout the Arctic and an example for such efforts elsewhere.

Anti-parasite treatment, but not mercury burdens, influence nesting propensity dependent on arrival time or body condition in a marine bird

Arctic wildlife can be exposed to high mercury (Hg) levels, and are also naturally exposed to gastrointestinal parasites that can reduce condition and negatively affect reproductive output and/or survival in similar ways. Importantly, both Hg and parasites are increasing in wildlife in some Arctic regions. We studied the northern common eider duck (Somateria mollissima) to explore how Hg in association with both natural levels and experimentally reduced parasitic infections, affect reproduction and survival. Female eiders were measured, banded, and blood sampled to determine blood Hg burdens, prior to breeding. Propensity to nest, clutch size, nest survival, nest attendance, and return rates were assessed in relation to both Hg burden and parasite treatment. Neither reproduction nor return rates of females varied with Hg concentrations, but females arriving late to the colony, or in low body condition, showed increased nesting propensity when given the anti-parasite treatment as compared to placebo treatment. Our results suggest that parasites can play a critical role in decisions to invest in avian breeding annually, particularly among individuals with a late onset to breeding, and in poor condition.

Does hyperthermia constrain flight duration in a short-distance migrant?

While some migratory birds perform non-stop flights of over 11 000 km, many species only spend around 15% of the day in flight during migration, posing a question as to why flight times for many species are so short. Here, we test the idea that hyperthermia might constrain flight duration (FD) in a short-distance migrant using remote biologging technology to measure heart rate, hydrostatic pressure and body temperature in 19 migrating eider ducks (Somateria mollissima), a short-distance migrant. Our results reveal a stop-and-go migration strategy where migratory flights were frequent (14 flights day(-1)) and short (15.7 min), together with the fact that body temperature increases by 1°C, on average, during such flights, which equates to a rate of heat storage index (HSI) of 4°C h(-1) Furthermore, we could not find any evidence that short flights were limited by heart rate, together with the fact that the numerous stops could not be explained by the need to feed, as the frequency of dives and the time spent feeding were comparatively small during the migratory period. We thus conclude that hyperthermia appears to be the predominant determinant of the observed migration strategy, and suggest that such a physiological limitation to FD may also occur in other species.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.

Implications of mercury and lead concentrations on breeding physiology and phenology in an Arctic bird

Although physiological traits and phenology are thought to be evolved traits, they often show marked variation within populations, which may be related to extrinsic factors. For example, trace elements such as mercury (Hg) and lead (Pb) alter biochemical processes within wildlife that may affect migration and breeding. While there is a growing understanding of how contaminants may influence wildlife physiology, studies addressing these interactions in free-living species are still limited. We examined how four non-essential trace elements (cadmium, Hg, Pb and selenium) interacted with physiological and breeding measures known to influence breeding in a free-living population of common eider ducks (Somateria mollissima). We collected blood from female eiders as they arrived at a breeding colony in northern Canada. Blood was subsequently assessed for baseline corticosterone (CORT), immunoglobulin Y (IgY), and the four trace elements. We used model selection to identify which elements varied most with CORT, IgY, arrival condition, and arrival timing. We then used path analysis to assess how the top two elements from the model selection process (Hg and Pb) varied with metrics known to influence reproduction. We found that arrival date, blood Hg, CORT, and IgY showed significant inter-annual variation. While blood Pb concentrations were low, blood Pb levels significantly increased with later arrival date of the birds, and varied negatively with eider body condition, suggesting that even at low blood concentrations, Pb may be related to lower investment in reproduction in eiders. In contrast, blood Hg concentrations were positively correlated with eider body condition, indicating that fatter birds also had higher Hg burdens. Overall, our results suggest that although blood Hg and Pb concentrations were below no-effect levels, these low level concentrations of known toxic metals show significant relationships with breeding onset and condition in female eider ducks, factors that could influence reproductive success in this species.

Direct and indirect causes of sex differences in mercury concentrations and parasitic infections in a marine bird

In many animal species, males and females differ in their levels of contaminants and/or parasitic infections. Most contaminants and gastro-intestinal parasites are obtained through prey ingestion, and thus the causes of sex differences in the distribution of these factors might follow similar pathways. We studied the northern common eider duck (Somateria molissima borealis) as an avian model, and used directed separation path analysis to explore the causes of sex differences in mercury (Hg) and gastro-intestinal helminths. Two trophically transmitted helminths were examined: a cestode (Lateriporus sp.) and an acanthocephalan (Polymorphus sp). We found that the number of Lateriporus sp. varied positively with stable isotope signature (as indicated by δ15N in eider breast muscle tissue), and negatively with crustaceans being present in the short term diet. We also found that Polymorphus sp. varied positively with eider tissue stable isotope signature. However, Polymorphus sp. varied negatively with sex indirectly through condition and liver mass. Similarly, Hg concentrations also varied negatively with sex indirectly through condition and liver mass, with both Polymorphus sp. intensity and Hg concentrations significantly higher in males. We found that model fit increased when a negative relationship between the two helminth species was included, suggesting a yet unknown causal mechanism linking these parasites. Our findings suggest that although Hg and gastro-intestinal parasites are both trophically transmitted through the eider's prey items, the factors that contribute towards bioaccumulation of these two burdens differ in source, likely caused by several different factors and may potentially influence each other.