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Where available, census data on seabirds often do not extend beyond a few years or decades, challenging our ability to identify drivers of population change and to develop conservation policies. Here, we reconstruct long-term population dynamics of northern common eiders ( Somateria mollissima borealis ). We analyzed sterols together with stable nitrogen isotopes in dated pond sediment cores to show that eiders underwent broadscale population declines over the 20th century at Canadian subarctic breeding sites. Likely, a rapidly growing Greenland population, combined with relocation of Inuit to larger Arctic communities and associated increases in the availability of firearms and motors during the early to mid-20th century, generated more efficient hunting practices, which in turn reduced the number of adult eiders breeding at Canadian nesting islands. Our paleolimnological approach highlights that current and local monitoring windows for many sensitive seabird species may be inadequate for making key conservation decisions., Competing Interests: The authors declare no conflict of interest., (Copyright © 2019 the Author(s). Published by PNAS.)

With changing climate, delineation of protected areas for sensitive species must account for long-term variability and geographic shifts of key habitat elements. Projecting the future adequacy of protected areas requires knowing major factors that drive such changes, and how readily the animals adjust to altered resources. In the Arctic, the viability of habitats for marine birds and mammals often depends on sea ice to dissipate storm waves and provide platforms for resting. However, some wind conditions (including weak winds during extreme cold) can consolidate pack ice into cover so dense that air-breathing divers are excluded from the better feeding areas. Spectacled Eiders (Somateria fischeri) winter among leads (openings) in pack ice in areas where densities of their bivalve prey are quite high. During winter 2009, however, prevailing winds created a large region of continuous ice with inadequate leads to allow access to areas of dense preferred prey. Stable isotope and fatty acid biomarkers indicated that, under these conditions, the eiders did not diversify their diet to include abundant non-bivalve taxa but did add a smaller, less preferred, bivalve species. Consistent with a computer model of eider energy balance, the body fat of adult eiders in 2009 was 33-35% lower than on the same date (19 March) in 2001 when ice conditions allowed access to higher bivalve densities. Ice cover data suggest that the eiders were mostly excluded from areas of high bivalve density from January to March in about 30% of 14 winters from 1998 to 2011. Thus, even without change in total extent of ice, shifts in prevailing winds can alter the areal density of ice to reduce access to important habitats. Because changes in wind-driven currents can also rearrange the dispersion of prey, the potential for altered wind patterns should be an important concern in projecting effects of climate change on the adequacy of marine protected areas for diving endotherms in the Arctic.

The king eider (Somateria spectabilis) is a migratory species of sea duck whose North American population is thought to be declining. We determined levels of cadmium, lead, selenium, and mercury in blood from female king eiders nesting in the central Canadian Arctic from 2001 to 2003. Year-to-year repeatability estimates were calculated from birds sampled in 2 or 3 years. Repeatability coefficients were 0.45, 0.35, 0.58, and 0.25 for cadmium, lead, selenium, and mercury, respectively. The first three were significantly different from zero (p < 0.05), whereas the last approached significance (0.05 < p < 0.1). In 2001 and 2002, we also identified probable wintering locations of a subset of the birds. In both years, cadmium levels were higher and selenium levels were lower in birds inferred to have wintered in the eastern part of their range compared to those that had wintered in the west. There was little evidence that timing of breeding, timing of sampling, or body condition were related to levels of these trace elements, although in 1 of 2 years, lead levels were influenced by body condition and nest initiation date (R(2) = 0.24) and cadmium levels were related to incubation day (partial R(2) = 0.04). Year-to-year repeatability of cadmium and selenium levels among individuals in this population of king eiders was likely influenced by where they wintered.

Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. Previous studies have shown that the acquired immunity of female common eider ducks (Somateria mollissima) is suppressed during their incubation, during which they entirely fast. Corticosterone was proposed to be an underlying physiological mechanism for such immunosuppression. Therefore, the current study aimed to assess the effects of exogenous corticosterone on acquired immunity in captive eiders. To this end, females were implanted with corticosterone pellets at different stages of their incubation fast. We measured total immunoglobulin levels, T-cell-mediated immune response, body mass and corticosterone levels in these females and compared them with those of control females prior to and after manipulation (i.e. corticosterone pellet implantation). To mimic corticosterone effects on body mass, we experimentally extended fasting duration in a group of females termed ;late fasters'. Implanted females had corticosterone levels 6 times higher and lost 35% more mass than control females. Corticosterone levels in ;late fasters' were similar to those in control females but body mass was 8% lower in the former. The decrease in the immunoglobulin levels of corticosterone implanted females was twice as high as in control females, while the T-cell-mediated immune response was not significantly affected by the treatment. We found a decrease in the T-cell-mediated immune response only in ;late fasters' (by 60%), while the immunoglobulin level was not lower in this group than in corticosterone implanted or control females. Our study shows that in incubating eiders, exogenous corticosterone only decreased humoral immunity. We suggest that the immunosuppressive effect of corticosterone could be mediated through its effects on body reserves. Further experiments are required to determine the relationship between body condition and immune system in fasting birds.

Concentrations and total organ content of mercury, selenium and cadmium, as well as liver, kidney and body mass were determined in female common eiders from 1997 to 2000 at the East Bay Migratory Bird Sanctuary in the eastern Canadian arctic. In 1997 and 1999, female eiders were collected during the pre-nesting period when they eat copious amounts of food and gain substantial weight in preparation for the rigours of nesting. In 1998 and 1999, female eiders were collected during the mid to late stages of the nesting period when they eat very little, if at all, and, as a consequence undergo dramatic weight loss. Total body mass, liver mass and kidney mass were highest in pre-nesting birds, especially in 1997. They were significantly lower in nesting birds collected in 1998 and 2000. In contrast, mercury and cadmium concentrations were lowest in pre-nesting birds collected in 1997 and 1999 and increased to significantly higher concentrations in nesting birds collected in 1998 and 2000. In contrast to these results, the total contents of mercury in liver and cadmium in kidney did not change significantly over the 4-year period. Hepatic selenium concentrations were relatively stable over the 4-year study period while changes in the total content of selenium in the liver paralleled changes in liver mass and body mass. The results suggest that mercury and cadmium concentrations in female common eiders change in response to normal changes in body and organ mass that occur during the reproductive period. Thus, it may be important to consider body condition or reproductive stage when using common eiders (and perhaps other species of sea ducks) in biomonitoring studies or when interpreting concentrations of metals in tissues in terms of the risk they pose to these ducks.

Adult long-tailed ducks (Clangula hyemalis) were collected from nine locations across their breeding grounds in northern Canada and measurements of stable isotopes of carbon (delta(13)C), nitrogen (delta(15)N) and sulfur (delta(34)S) in bone collagen were used to investigate if relative use of freshwater habitats such as the Great Lakes (with expected depleted stable isotope profiles) compared with coastal marine environments (with expected enriched stable isotope foodweb profiles) could explain tissue trace element profiles. Contrary to expectation, all three stable isotopes did not covary in our sample, suggesting that mechanisms other than simple freshwater vs. marine isotopic gradients were involved among populations. All three stable isotopes varied significantly with collection location and both delta(15)N and delta(13)C values varied significantly between sexes suggesting that males exploit either a different food base or occur in different geographic areas than females for at least part of the year. The delta(34)S data, in particular, suggested that many of the birds breeding in the western Canadian Arctic probably overwinter in the Great Lakes along with many of the birds breeding in Hudson Bay. Males at the majority of collection locations had higher concentrations of hepatic Hg (1.1-8 microg/g dw), Cu (25-40 mug/g dw), Se (7.3-27 mug/g dw) and renal Cd (33-129 microg/g dw) than females. Concentrations of Hg, Cu and Cd were well below toxicological threshold levels found in the literature. However, hepatic Se concentrations in 64% of the females exceeded 10 mug/g dw and concentrations in 8% of the birds measured exceeded 33 microg/g dw suggesting levels of potential concern.

We examined relationships between trace metal concentrations in tissues of common eider ducks (cadmium, mercury, and selenium) and selected biomarkers of health (stress response, immune function, and body condition). This study was conducted at an eider nesting colony in the Canadian arctic in 1998 and 1999. Capture-induced stress, measured as the rise in corticosterone concentrations following capture, was positively related (P=0.03) to renal cadmium concentration in 1998 when incubating eiders were sampled, but not in 1999 when prenesting eiders were sampled. Stress response was inversely related (P=0.02) to selenium concentrations in 1999. Following capture and blood sampling in 1999, eiders were placed in a flight pen on-site for eight days in order to examine immune function. Cell-mediated immunity, measured as the skin-swelling response to an intradermal injection of phytohemagglutinin-P, (PHA-P), was positively related (P=0.003) to hepatic selenium. The heterophil:lymphocyte ratio was inversely related (P=0.08) to hepatic selenium. In 1998, selenium was positively related to body mass (P=0.01), abdominal fat mass (P=0.07), kidney mass (P=0.03), and liver mass (P=0.07). In 1999, hepatic mercury was negatively related to abdominal fat mass (P=0.01), spleen mass (P=0.07) and body mass at capture (P=0.09) in prenesting eiders.

We review nesting sea duck population declines in Alaska during recent decades and explore the possibility that contaminants may be implicated. Aerial surveys of the surf scoter (Melanitta perspicillata), white-winged scoter (M. fusca), black scoter (M. nigra), oldsqaw (Clangula hyemalis), spectacled eider (Somateria fischeri), and Steller's eider (Polysticta stellei) show long-term breeding population declines, especially the latter three species. The spectacled eider was recently classified threatened under the Endangered Species Act. In addition, three other diving ducks, which commonly winter in coastal areas, have declined from unknown causes. Large die-offs of all three species of scoters during molt, a period of high energy demand, were documented in August 1990, 1991, and 1992 at coastal reefs in southeastern Alaska. There was no evidence of infectious diseases in those scoters. The die-offs may or may not be associated with the long-term declines. Many scoters had elevated renal concentrations of cadmium (high of 375 micrograms/g dry weight [dw]). Effects of cadmium in sea ducks are not well understood. Selenium concentrations in livers of nesting white-winged scoters were high; however, the eggs they laid contained less selenium than expected based on relationships for freshwater bird species. Histological evaluation found a high prevalence of hepatocellular vacuolation (49%), a degenerative change frequently associated with sublethal toxic insult. Cadmium and selenium mean liver concentrations were generally higher in those birds with more severe vacuolation; however, relationships were not statistically significant. We do not know if sea duck population declines are related to metals or other contaminants.