Showing papers by "Keith A. Hobson published in 2011"

Methylmercury photodegradation influenced by sea-ice cover in Arctic marine ecosystems

Abstract: Atmospheric deposition of mercury to remote areas has increased threefold since pre-industrial times. Mercury deposition is particularly pronounced in the Arctic. Following deposition to surface oceans and sea ice, mercury can be converted into methylmercury, a biologically accessible form of the toxin, which biomagnifies along the marine food chain. Mass-independent fractionation of mercury isotopes accompanies the photochemical breakdown of methylmercury to less bioavailable forms in surface waters. Here we examine the isotopic composition of mercury in seabird eggs collected from colonies in the North Pacific Ocean, the Bering Sea and the western Arctic Ocean, to determine geographical variations in methylmercury breakdown at northern latitudes. We find evidence for mass-independent fractionation of mercury isotopes. The degree of mass-independent fractionation declines with latitude. Foraging behaviour and geographic variations in mercury sources and solar radiation fluxes were unable to explain the latitudinal gradient. However, mass-independent fractionation was negatively correlated with sea-ice cover. We conclude that sea-ice cover impedes the photochemical breakdown of methylmercury in surface waters, and suggest that further loss of Arctic sea ice this century will accelerate sunlight-induced breakdown of methylmercury in northern surface waters. Atmospheric deposition of mercury to remote areas has increased threefold since pre-industrial times. Reductions in sea-ice cover accelerate the photodegradation of biologically accessible mercury in Arctic waters, according to an analysis of the isotopic composition of bird eggs in northern latitudes.

Isotopic ornithology: a perspective

Abstract: The use of measurements of naturally occurring stable isotopes of the light elements C, N, H, O, S in avian tissues and their associated foodwebs has grown tremendously during the last 30 years. Three primary applications of this approach have been (1) the delineation of diets or trophic relationships and sources of nutrients to individuals or populations, (2) the assessment of the relative contributions of endogenously and exogenously derived nutrients to reproduction in birds that travel to breed, and, more recently, (3) the assignment to origin of migratory individuals. This paper will briefly summarize the roots of these theme areas and highlight the benefits of an isotope perspective. However, the primary focus of this paper is on key assumptions, misunderstandings, information gaps and the path ahead. Specific recommendations for future research are outlined for all of these theme areas. Finally, a plea is made for more constructive criticism in the field of isotopic applications to animal ecological studies, especially those involving birds.

Combining stable-isotope (δD) and band recovery data to improve probabilistic assignment of migratory birds to origin

Abstract: The recent application of stable-isotope analyses, particularly the use of stable-hydrogen-isotope (deltaD) measurements of animal tissues, has greatly improved our ability to infer geographic origins of migratory animals. However, many individual sources of error contribute to the overall error in assignment; thus likelihood-based assignments incorporating estimates of error are now favored. In addition, globally, the nature of the underlying precipitation-based deltaD isoscapes is such that longitudinal resolution is often compromised. For example, in North America, amount-weighted expected mean growing-season precipitation deltaD is similar between the boreal forest of southwestern Canada and areas of northern Quebec/Labrador and Alaska. Thus, it can often be difficult to distinguish objectively between these areas as potential origins for broadly distributed migrants using a single isotopic measurement. We developed a Bayesian framework for assigning geographic origins to migrant birds based on combined stable-isotope analysis of feathers and models of migratory directions estimated from band recovery data. We outline our method and show an example of its application for assigning origins to a population of migrant White-throated Sparrows (Zonotrichia albicollis) sampled at a Canadian Migration Monitoring Network station at Delta Marsh, Manitoba, Canada. We show that likelihood-based assignments of geographic origins can provide improved spatial resolution when models of migration direction are combined with assignments based on deltaD analysis of feathers.

Fast carnivores and slow herbivores: differential foraging strategies among grizzly bears in the Canadian Arctic

Abstract: Categorizing animal populations by diet can mask important intrapopulation variation, which is crucial to understanding a species’ trophic niche width. To test hypotheses related to intrapopulation variation in foraging or the presence of diet specialization, we conducted stable isotope analysis (δ13C, δ15N) on hair and claw samples from 51 grizzly bears (Ursus arctos) collected from 2003 to 2006 in the Mackenzie Delta region of the Canadian Arctic. We examined within-population differences in the foraging patterns of males and females and the relationship between trophic position (derived from δ15N measurements) and individual movement. The range of δ15N values in hair and claw (2.0–11.0‰) suggested a wide niche width and cluster analyses indicated the presence of three foraging groups within the population, ranging from near-complete herbivory to near-complete carnivory. We found no linear relationship between home range size and trophic position when the data were continuous or when grouped by foraging behavior. However, the movement rate of females increased linearly with trophic position. We used multisource dual-isotope mixing models to determine the relative contributions of seven prey sources within each foraging group for both males and females. The mean bear dietary endpoint across all foraging groups for each sex fell toward the center of the mixing polygon, which suggested relatively well-mixed diets. The primary dietary difference across foraging groups was the proportional contribution of herbaceous foods, which decreased for both males and females from 42–76 to 0–27% and 62–81 to 0–44%, respectively. Grizzlies of the Mackenzie Delta live in extremely harsh conditions and identifying within-population diet specialization has improved our understanding of varying habitat requirements within the population.

Do purely capital layers exist among flying birds? Evidence of exogenous contribution to arctic-nesting common eider eggs

Abstract: The strategy of relying extensively on stored resources for reproduction has been termed capital breeding and is in contrast to income breeding, where needs of repro- duction are satisWed by exogenous (dietary) resources. Most species likely fall somewhere between these two extremes, and the position of an organism along this gradi- ent can inXuence several key life-history traits. Common eiders (Somateria mollissima) are the only Xying birds that are still typically considered pure capital breeders, suggest- ing that they depend exclusively on endogenous reserves to form their eggs and incubate. We investigated the annual and seasonal variation in contributions of endogenous and exogenous resources to egg formation in eiders breeding at the East Bay colony in the Canadian Arctic. We collected prey items along with females and their eggs during various stages of breeding and used two complementary analytical approaches: body reserve dynamics and stable isotope ( 13 C, 15 N) mixing models. Indices of protein reserves remained stable from pre-laying to post-laying stages, while lipid reserves declined signiWcantly during laying. Similarly, stable isotope analyses indicated that (1) exoge- nous nutrients derived from marine invertebrates strongly contributed to the formation of lipid-free egg constituents, and (2) yolk lipids were constituted mostly from endoge- nous lipids. We also found evidence of seasonal variation in the use of body reserves, with early breeders using pro- portionally more exogenous proteins to form each egg than late breeders. Based on these results, we reject the hypothe- sis that eiders are pure capital layers. In these Xying birds, the Wtness costs of a strict capital breeding strategy, such as temporary loss of Xight capability and limitation of clutch and egg size, may outweigh beneWts such as a reduction in egg predation rate.

Quantifying dietary pathways of proteins and lipids to tissues of a marine predator

Abstract: 1. Using measurements of naturally occurring stable isotopes in animal tissues is useful for monitoring diets of wide-ranging species that would otherwise be logistically difficult to evaluate. However, differential metabolic routing of macromolecules within a consumer can be problematic when using stable isotope analysis of bulk tissues to trace dietary input. 2. We used stable isotope (δ13C, δ15N) analysis to examine polar bear Ursus maritimus diet, which includes both lipid-rich blubber and the proteinaceous tissues of their marine mammal prey. Because the proportion of proteins and lipids consumed may depend on prey type and size, it was necessary to consider metabolic routing of these macromolecules separately in isotope mixing models. 3. Bayesian mixing models (MixSIR, version 1.04) were used to separately estimate protein (δ13C, δ15N) and lipid (δ13C) dietary inputs. We used existing knowledge of the relative lipid and protein intake for polar bears and isotopic information from both macromolecules to estimate overall diet composition. 4. The results for both male and female polar bears indicated that smaller prey (e.g. ringed seal Pusa hispida) contributed the largest proportion to the protein-metabolic pathway. In contrast, the largest proportion of the lipid-metabolic pathway for both sexes tended to consist of larger prey (e.g. bearded seal Erignathus barbatus). 5. The diet composition of male polar bears consisted of more large than small prey. Diet estimates for females overlapped to some degree with males but tended to consist of less large prey. 6. Synthesis and applications. Monitoring polar bear diet may help determine the effects of climate-induced environmental changes in Arctic marine ecosystems including shifts in prey composition. Additionally, tracing origins of anthropogenic pollutants is currently a priority for wildlife managers concerned with the health of marine mammals. However, our results indicate using stable isotopes to infer dietary inputs when proportions of macromolecules fluctuate amongst food sources requires the sampling and analysis of multiple tissues representing distinct macromolecular metabolic pathways. In such cases, utilizing only proteinaceous tissues for analysis will result in erroneous dietary source estimates and inaccuracies when examining trophic-level transfer of contaminants, especially those that are lipophylic.

Tracking Cats: Problems with Placing Feline Carnivores on δ18O, δD Isoscapes

Abstract: Background Several felids are endangered and threatened by the illegal wildlife trade. Establishing geographic origin of tissues of endangered species is thus crucial for wildlife crime investigations and effective conservation strategies. As shown in other species, stable isotope analysis of hydrogen and oxygen in hair (δDh, δ18Oh) can be used as a tool for provenance determination. However, reliably predicting the spatial distribution of δDh and δ18Oh requires confirmation from animal tissues of known origin and a detailed understanding of the isotopic routing of dietary nutrients into felid hair.

Effects of size and diet on stable hydrogen isotope values (δD) in fish: implications for tracing origins of individuals and their food sources

Abstract: Recent studies suggest that stable hydrogen isotope ratios (δD) of fish can be used to track their watershed origin and the relative contributions of source material. Both applications assume that ...

Lekking birds in a tropical forest forego sex for migration

Abstract: Facultative, partially migratory animals provide a contemporary window into the evolution of migration, offering rare opportunities to examine the life-history trade-offs associated with migration. For the first time, to our knowledge, we describe the nature of these trade-offs, using a lek-breeding tropical bird, the white-ruffed manakin (Corapipo altera). Previous evidence indicated that weather drives post-breeding migration to lower elevations bringing condition-related benefits. Using elevation-sensitive stable isotope measurements and more than 1200 h of behavioural observations, we show that male manakins which migrate incur costs of diminished social status and matings with females the following breeding season. Because migratory tendency depends on inter-annual variation in weather, physical costs of displays and breeding prospects the following year, migratory decisions are subject to both natural and sexual selection, with the outcome of such decisions linked to changing climatic regimes.

Tracking large carnivore dispersal using isotopic clues in claws: an application to cougars across the Great Plains

Abstract: Summary 1. Cougar (Puma concolor) populations, like other large carnivores, have increased during recent decades and may be recolonizing their former ranges in Midwestern North America. The dispersal routes taken by these animals from established populations are unknown and insight into these movements would facilitate their conservation and management. 2. We inferred the origin and migration route of four dispersing cougars using stable hydrogen (dD) and carbon (d 13 C) isotope values along one of their claws. We compared isotopic variations within claws to regional and large-scale isoscapes of d Da ndd 13 C values in prey species. Using a likelihood-based assignment approach, we predicted the most likely dispersal route of each cougar (among several least-cost dispersal paths to potential source populations) in a chronological sequence dating back from its final location. 3. Our model predicted the origin of a radio-collared short-distance disperser and inferences about the most likely dispersal corridors for two long-distance dispersers matched reported information from re-sighting events and genetic investigations. 4. Insights about the most likely migration corridors may help identify critical areas and guide future conservation efforts of cougars and other large carnivores. We encourage managers to extend regional isoscapes based on sedentary prey species as they prove to be valuable tools in isotopic tracking of long-distance migration. 5. Our isotopic approach may be extended to other metabolically inert tissues that grow continuously, to investigate dispersal paths of species of interest, providing that individuals disperse across known isotopically structured landscapes.

Monarch butterflies cross the Appalachians from the west to recolonize the east coast of North America.

Abstract: Each spring, millions of monarch butterflies (Danaus plexippus) migrate from overwintering sites in Mexico to recolonize eastern North America. However, few monarchs are found along the east coast of the USA until mid-summer. Brower (Brower, L. P. 1996 J. Exp. Biol. 199, 93–103.) proposed that east coast recolonization is accomplished by individuals migrating from the west over the Appalachians, but to date no evidence exists to support this hypothesis. We used hydrogen (δD) and carbon (δ13C) stable isotope measurements to estimate natal origins of 90 monarchs sampled from 17 sites along the eastern United States coast. We found the majority of monarchs (88%) originated in the mid-west and Great Lakes regions, providing, to our knowledge, the first direct evidence that second generation monarchs born in June complete a (trans-) longitudinal migration across the Appalachian mountains. The remaining individuals (12%) originated from parents that migrated directly from the Gulf coast during early spring. Our results provide evidence of a west to east longitudinal migration and provide additional rationale for conserving east coast populations by identifying breeding sources.

Morphometrics and stable isotopes differentiate populations of Northern Wheatears (Oenanthe oenanthe)

Abstract: Linking events of breeding, wintering and stopover areas has important ecological and conservation implications for migratory species. To find a tool to connect these different events in a long-distance migrating songbird, the Northern Wheatear Oenanthe oenanthe, we applied a discriminant analysis based on morphometrics and analysed stable isotope values (δ13C, δ15N, δD) in feathers. Morphometric differences were additionally analysed with respect to wing shape as an adaptation to migration routes. Discriminant analysis 100% separated a group of long-winged migrants passing the German offshore island of Helgoland from Icelandic and Norwegian breeding birds, as well as from Northern Wheatears passing the Baltic Sea coast on migration. This clear assignment suggests a Greenlandic origin of these long-winged Northern Wheatears. The most likely Greenlandic origin was further supported by depleted δD values in feathers of these birds grown on the breeding grounds. We found a relatively high proportion of presumed Greenlandic birds on Helgoland and especially on Fair Isle (Scotland) during spring migration. Morphometric differences were based mainly on wing morphology and could be successfully connected with migration routes. Presumed Greenlandic Northern Wheatears showed more pointed wings than birds from other European breeding areas. Such wings might be natural selection’s solution for the long obligatory non-stop flights during the Atlantic crossings.

Geographic Origins and Timing of Fall Migration of the Veery in Northern Colombia

Abstract: . Establishing migratory connectivity between migratory birds' breeding, wintering, and stopover sites is an important component of their effective conservation and management. For neotropical migrants, geographic origins and migration patterns have been poorly documented. During fall migration of 2009, we identified geographic origins of the Veery (Catharus fuscescens) at stopover sites in the Sierra Nevada de Santa Marta, northern Colombia, by analyzing stable hydrogen isotopes (δD) in feathers and from values expected from a long-term isoscape for North America of δD in feathers. We evaluated the importance of the Sierra Nevada de Santa Marta to the Veery on the basis of the birds' geographic origins and assessed the relationship between timing of migration and geographic origins and age. We estimated that 100 of the 197 individuals captured originated from the southwest and/or the northeast regions of their breeding range, but applying abundance in the breeding range as an informed prior proba...

9. Understanding Declines In Rusty Blackbirds

Abstract: Wells_6480005_watermark.indd 1 10/20/11 1:40 PM 107 Abstract. The Rusty Blackbird (Euphagus carolinus), a formerly common breeding species of boreal wetlands, has exhibited the most marked decline of any North American landbird. North American Breeding Bird Survey (BBS) trends in abundance are estimated to be 12.5%/yr over the last 40 years, which is tantamount to a 95% cumulative decline. Trends in abundance calculated from Christmas Bird Counts (CBC) for a similar period indicate a range-wide decline of 5.6%/yr. Qualitative analyses of ornithological accounts suggest the species has been declining for over a century. Several studies document range retraction in the southern boreal forest, whereas limited data suggest that abundance may be more stable in more northerly areas. The major hypotheses for the decline include degradation of boreal habitats from logging and agricultural development, mercury contamination, and wetland desiccation resulting from global warming. Other likely reasons for decline include loss or degradation of wooded wetlands of the southeastern U.S and mortality associated with abatement efforts targeting nuisance blackbirds. In addition, the patchy breeding distribution of this species may inhibit population consolidation, causing local populations to crash when reduced to low levels. Progress in understanding the causes and mechanisms for observed declines has remained limited until recently. Here we present initial attempts to understand the habitat requirements of Rusty Blackbirds and offer specific predictions associated with each of the hypotheses for decline as a way of guiding future research.

Exploiting the closest productive area: geographical segregation of foraging grounds in a critically endangered seabird

Abstract: While breeding, seabirds are limited to exploiting resources within a restricted area around their breeding site and should exploit the closest productive marine areas within their distri- bution range. We investigated this hypothesis in one of the most endangered European seabirds, the Balearic shearwater Puffinus mauretanicus (ca. 3200 breeding pairs), restricted to the Balearic Islands. Our aims were (1) to assess whether isotopic evidence (i.e. stable isotopes of � 13 C and � 15 N) of foraging habitat partitioning occurs among northern, central and southern populations, (2) to geo- graphically locate population-specific potential foraging grounds along the Iberian continental shelf, and (3) to assess whether oceanographic conditions could explain observed patterns of stable iso- topes (SI). SI values showed a latitudinal gradient, with birds from the northern population having lower � 15 N and � 13 C values than central and southern populations. Potential foraging grounds of northern, central and southern populations were centred in Cape Creus, Ebro Delta and Cape La Nao, respectively, results which were supported by habitat models. Oceanographic conditions in each potential foraging ground were different; the northern population used richer, colder and deeper waters compared to the central and southern populations. Chlorophyll a was the main oceanographic variable that explained variation in SI values. We hypothesised that SI differences among Balearic shearwater populations might be a consequence of differences in baseline isotopic values among potential foraging grounds rather than real differences in diet. Our comprehensive study also provides important information for management strategies to conserve this critically endangered shearwater.

Nutrient Allocation Strategies to Eggs by Lesser Snow Geese (Chen caerulescens) at a Sub-Arctic Colony

Abstract: . The relative allocation of endogenous- and exogenous-derived nutrients to reproductive investment in Arctic-nesting geese is affected by body size, migration distance, and proximate conditions on the wintering, staging, and breeding grounds prior to clutch initiation. We used δ13C and δ15N measurements of muscle tissue and egg lipid-free yolk and albumen and δ13C analysis of abdominal fat and egg yolk lipids, together with isotopic analyses of foraging plants, to quantify the relative use of endogenous and exogenous reserves in egg production in a breeding population of sub-Arctic Lesser Snow Geese (Chen caerulescens caerulescens) on the Cape Churchill Peninsula, Manitoba, from 2005 to 2008. We used a concentration-dependent, two-isotope, three-source Bayesian (SIAR) mixing model to derive estimates of endogenous reserves to egg macronutrients and a single-isotope (δ13C), two-source (exogenous vs. endogenous) Bayesian model to estimate the source of lipids to eggs. Endogenous protein contributio...

Interannual Flexibility in Breeding Phenology of a Neotropical Migrant Songbird in Response to Weather Conditions at Breeding and Wintering Areas

Abstract: Changes in climate that affect breeding phenology can have important ramifications for the population dynamics of migratory wildlife. In birds, predicted changes in global climate raise concerns over the ability of migratory species, especially long-distance migrants, to adapt to changes in spring weather conditions. At a riparian breeding site in southern Manitoba, we found that over 3 decades (1974 to 2003), migratory yellow warblers (Dendroica petechia) exhibited considerable plasticity in their timing of clutch initiation in response to mean May temperatures at the breeding site. Spring arrival dates estimated during the last 9 y of our study were also highly variable and correlated with mean May temperatures. By contrast, we found no support for an effect of the El Nino/Southern Oscillation, a climatic phenomenon known to affect weather conditions on wintering grounds of yellow warblers, on spring arrival dates or timing of breeding. This suggests that El Nino/ Southern Oscillation did not ...

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δ13C, δ15N and δD) as environmental tracers

Abstract: Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ 13 C, δ 15 N and δD measurements of a euryhaline fish, the Mediterranean toothcarp ( Aphanius fasciatus ), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern ( Sternula albifrons ) and Little Egret ( Egretta garzetta ), was inferred trough a triple-isotope (δ 13 C, δ 15 N and δD) Bayesian mixing model. Isotopic trends for fish δ 15 N and δD across the salinity gradient followed the equations: δ 15 N = e (1.1 + 47.68/Salinity) and δD = −175.74 + Salinity + Salinity 2 ; whereas fish δ 13 C increased as salinity rose (δ 13 C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ 13 C for salinities

Stable Isotopes (δD) Reveal East—West Differences in Scheduling of Molt and Migration in Northern Rough-Winged Swallows (Stelgidopteryx serripennis)

Abstract: . We used stable-isotope (δD) measurements of primary feathers to demonstrate that Northern Rough-winged Swallows (Stelgidopteryx serripennis) that breed in western North America migrate to the monsoon region of northwest Mexico for their annual postbreeding molt. Both adults and juveniles replace all their primaries in late summer. As expected, in samples of adults and fledglings collected at a northern breeding locality in eastern Washington, primary δD values of adults were of southern origin, whereas those of fledglings, whose feathers were grown in the nest, were consistent with their northern origin. Similarly, some young birds collected as they were replacing primaries in northwest Mexico had a southern signature in newly replaced primaries but a northern signature in their yet unreplaced juvenile primaries, which indicates that they were molt migrants from the north. Feather OD values increased from P1 to P9 in breeding adults collected in upstate New York. In the eastern United States, bo...

Endogenous contributions to egg protein formation in lesser scaup Aythya affinis

Abstract: Lesser scaup Aythya affinis populations have declined throughout the North American continent for the last three decades. It has been hypothesized that the loss and degradation of staging habitats has resulted in reduced female body condition on the breeding grounds and a concomitant decline in productivity. We explored the importance of body (endogenous) reserves obtained prior to arrival on the breeding ground in egg protein formation in southwestern Montana during 2006–2008 using stable-carbon (δ13C) and nitrogen (δ15N) isotope analyses of scaup egg components, female tissue, and local prey items. From arrival on the breeding grounds through the egg-laying period, δ15N values of scaup red blood cells decreased while δ13C values became less variable; a pattern consistent with endogenous tissues equilibrating with local (freshwater) dietary sources. In 2006 and 2008, isotopic values for egg albumen and yolk protein indicated that most (>90%) protein used to produce these components was obtained on the breeding grounds. However, in 2007, a year with an exceptionally warm and dry spring, endogenous reserves contributed on average 41% of yolk and 29% of albumen. Results from this study suggest that female scaup can meet the protein needs of egg production largely from local dietary food sources. This highlights the importance of providing high-quality breeding habitats for scaup. Whether this pattern holds in areas with similar breeding season lengths but longer migration routes, such as those found in the western boreal forest, should be investigated.

Combining Stable-Isotope and Body-Composition Analyses to Assess Nutrient-Allocation Strategies in Breeding White-Winged Scoters (Melanltta fusca)

Abstract: . Birds meet the energy and nutrient demands of egg formation by using dietary (exogenous) sources, somatic (endogenous) nutrients, or combinations of both. Therefore, understanding plasticity in resource acquisition and the allocation strategies that are used is important for predicting how ecosystem changes across a species' range could affect vital rates. Sources of egg nutrients have traditionally been assessed through analyses of body composition, but stable-isotope analysis has provided a new tool in cases where animal tissues differ isotopically from the local food webs where they breed. We provide the first simultaneous comparison of these two techniques and test the “seasonally variable nutrient threshold hypothesis.” Using body-composition analysis of White-winged Scoters (Melanitta fusca) collected at the northern extent of their range, we inferred that protein in rapidly developing ovarian follicles was derived entirely from dietary sources but that follicle lipids were most likely der...

Geographic differences in organic contaminants and stable isotopes (δ13C, δ15N) in thick-billed murre (Uria lomvia) eggs from Alaska

Abstract: The contents from thick-billed murre (Uria lomvia) eggs collected at four Alaskan colonies in 2002 were analyzed for organic contaminants and carbon (δ13C) and nitrogen (δ15N) stable isotopes. Contaminant concentrations in the eggs varied from below detection limits to 230 ng g−1 wet mass for 4,4′-DDE in one egg from St Lazaria Island in the Gulf of Alaska. Eggs from this colony generally contained higher levels of contaminants and exhibited significantly different patterns compared to eggs from the Bering and Chukchi seas. Stable isotope values also varied geographically; however, these differences appeared to be related to differences in C and N baselines in the food webs instead of differences in prey. Contaminant and stable isotope correlations were inconclusive, suggesting that better information on regional food web differences and differential offloading of contaminants and stable isotopes to the eggs must be obtained before these kinds of data can be fully incorporated into seabird egg contaminant monitoring programs.

Tracing waterbird exposure to total mercury and selenium: a case study at the solar saltworks of Thyna (sfax, Tunisia).

Abstract: Saltworks have emerged as important alternative/complementary feeding habitats for avifauna. However, the consequences of such habitat shifts in terms of changes in exposure to contaminants are poorly understood. We evaluated the exposure of the waterbird community breeding at the saltworks of Thyna (Tunisia) to total Hg (THg) and Se according to their differential use of saltworks dietary resources, as revealed by δ13C and δ15N values in their eggs (included species [n] -sorted according to increasing reliance on saltworks resources: Yellow-legged Gull Larus michahellis [12], Common Tern Sterna hirundo [12], Slender-billed Gull Larus genei [15], Little Egret Egretta garzetta [20], and Pied Avocet Recurvirostra avosetta [22]). Concentrations of THg and Se were under the threshold points for deleterious effects. Egg THg concentrations significantly decreased as the dietary contribution of saltworks resources increased (mean: 3.23, 1.66, 0.76, 0.4, and 0.27 μg/g dw, respectively). Conversely, egg Se concent...