Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds (original) (raw)
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PLOS ONE, 2015
In the Laurentian Great Lakes region, the double-crested cormorant (Phalacrocorax auritus) has seen a thousand-fold population increase in recent decades. These large colonies of birds now often conflict with socioeconomic interests, particularly due to perceived competition with fisheries and the destruction of terrestrial vegetation in nesting habitats. Here we use dated sediment cores from ponds on islands in eastern Lake Ontario that receive waste inputs from dense colonies of cormorants and ring-billed gulls (Larus delawarensis)to chronicle the population rise of these species and assess their long-term ecological impacts. Modern water chemistry sampling from these sites reveals drastically elevated nutrient and major ion concentrations compared to reference ponds not influenced by waterbirds. Geochemical tracers in dated sediment cores, particularly δ 15 N and chlorophyll-a concentrations, track waterbird influences over time. Fossil diatom assemblages were dominated by species tolerant of hyper-eutrophic and polluted systems, which is in marked contrast to assemblages in reference sites. In addition to establishing long-term ecological impacts, this multi-proxy paleoecological approach can be used to determine whether islands of concern have been long-term nesting sites or were only recently colonized by cormorant or ring-billed gull populations across the Great Lakes, facilitating informed management decisions about controversial culling programs.
The Auk, 1997
crested Cormorants (Phalacrocorax auritus) collected from Lake Ontario, Canada, to examine the extent to which nutrient reserves acquired on marine wintering grounds are transferred to eggs laid on freshwater breeding grounds. In order to establish isotopic patterns typical of eggs of birds using marine and freshwater C-3 biomes, eggs of Herring Gulls (Larus argentatus), a year-round resident on the Great Lakes, and those of Caspian Terns and Herring Gulls, breeding resepectively in the Gulf Coast of Texas and Atlantic Coast of Canada, were analyzed isotopically. Individual egg components showed distinct isotope values that were similar for both migratory and nonmigratory birds breeding in a freshwater biome and significantly lighter than those breeding in a marine biome. Hence, there appeared to be little evidence for significant nutrient transfer between the two biomes. The intermediate isotope values shown for egg components of Herring Gulls breeding on the Atlantic Coast suggest nutrient input from terrestrial as well as marine sources. Our results indicate the utility of stable-isotope analysis for tracing endogenous and exogenous contributions to reproduction in birds and further validate the use of migratory birds as indicators of breeding area contaminant levels and their effects on the Great Lakes.
Marine Biology, 1989
The role of marine mammals in the biogeochemical flux of oceanic carbon is largely unknown. Capillary gas chromatography and gas chromatography/mass spectrometry after organic solvent extraction and compound class separation of feces from cetaceans (toothed and baleen whales), pinnipeds and penguins (collected in 1987 from Monterey Bay, off the coast of California or from Sea World, San Diego, California, USA) indicate that the unusual sterol profile in the Antarctic sediments, with epicoprostanol predominating over its isomer, coprostanol, originates from baleen whales (blue and fin whales). The sterol distribution in feces from baleen whales is different from that of other animals studied here and also from anthropogenic sewage (collected in 1987 from wastewater outfalls off the coast of southern California, USA). The data from the current investigation thus provide the first geochemical evidence of a recognizable native mammalian contribution to the flux of carbon in the ocean. The results also illustrate how the marine mammalian contribution can be delineated from human impact around many coastal regions of the globe including Antarctic research stations. The relative distribution of the two isomers in the sediments deposited during preanthropogenic periods could help evaluate the historical migratory routes and habitats of cetaceans, pinnipeds and penguins. The presence of coprostanone in marine mammalian feces, which has also previously been detected in human feces, implies that at least part of the conversion of cholesterol into coprostanol in the intestine of marine mammals occurs via the formation of an intermediate, A 4-cholesten-3one.
Environmental Pollution, 2020
Assessing the fate of both legacy and newer persistent organic pollutants (POPs) is an ongoing challenge. Top predators, including seabirds, are effective monitors of POPs because they forage over a range of marine habitats, integrating signals over space and time. However, migration patterns can make unravelling contaminant sources, and potentially assessments of the effectiveness of regulations, challenging if chemicals are acquired at distant sites. In 2014, we fitted geolocators on ancient murrelets (Synthliboramphus antiqueus) at four colonies on the Pacific Coast of Canada to obtain movement data throughout an annual cycle. All birds underwent a post-breeding moult in the Bering Sea. Around onethird then returned to overwinter on the British Columbia (BC) coast while the rest migrated to overwinter in waters along the north Asian coast. Such a stark difference in migration destination provided an opportunity to examine the influence of wintering location on contaminant signals. In summer 2015, we collected blood samples from returned geo-tagged birds and analyzed them for a suite of contaminants, including polybrominated diphenyl ethers (PBDEs), non-PBDE halogenated flame retardants, perfluoroalkyl substances (PFASs), organochlorines, and mercury. Feathers were also collected and analyzed for stable isotopes (d 13 C, d 15 N, and d 34 S). We found no significant differences in blood concentrations of any contaminant between murrelets from the two different overwinter areas, a result that indicates relatively rapid clearance of POPs accumulated during winter. Spatial variation in diet (i.e., d 13 C) was associated with both BDE-47 and-99 concentrations. However, individual variation in trophic level had little influence on concentrations of any other examined contaminants. Thus, blood from these murrelets is a good indicator of recent, local contaminants, as most signals appear independent of overwintering location.
The Condor
Understanding the catchment areas of key stopover sites for migratory birds is important for their management and conservation. The Saskatchewan River Delta (SRD) in central Canada is North America's largest inland delta and an important spring and fall stopover site for migratory waterfowl, but there is little information on the origins of waterfowl that use the SRD. We used stable isotope analyses of hydrogen (d 2 H) and sulfur (d 34 S) in feathers of hunterkilled waterfowl on the SRD to infer natal or molt origins of 5 duck species, using spatially explicit assignment to a d 2 H feather isoscape developed for waterfowl in North America. Initial classification with d 2 H estimated that 50% were migrants from the north and 10% were assigned to regions south of the SRD, leaving only 39% of the sample with origins in the SRD. Using thresholds in feather d 34 S values associated with prairie and forest biomes, we further reassigned 64% of SRD birds as having originated from nearby agricultural and forested areas that have similar d 2 H values as the delta. Together, these results suggest that .80% of all waterfowl sampled were recent arrivals that were using the SRD as a stopover site. This demonstrates that stable isotope analyses of hunter-killed birds can be used to monitor changes in origins and recruitment into the fall waterfowl population of key stopover sites.
Freshwater Biology, 2009
1. We examined whether egg fatty acid (FA) profiles and stable isotopes (SIA) could be used in a comparative way to infer the diet of two aquatic bird species with contrasting feeding habits: a surface forager, the pheasant-tailed jacana (Hydrophasianus chirurgus), and a pursuit-diving forager, the little cormorant (Phalacrocorax niger), at Haleji Lake (Pakistan). 2. The species differed markedly in the overall percentage of saturated and polyunsaturated fatty acids. Moreover, among jacanas, two groups of birds had relatively high or low concentrations of long-chain essential PUFAs (such as 18:2 n-6 and 20:4 n-6), suggesting differing contributions from animal prey and plant material. 3. These trophic differences were corroborated by d 15 N values which indicated both a higher trophic position in cormorants relative to jacanas, and differences in trophic position for the two groups of jacanas. In this latter species d 13 C values in both groups also pointed to differing diets, involving mainly grazing plants or a contribution from animal resources (aquatic invertebrates or insects). 4. Both lower values of d 13 C and higher percentages of 18:1 n-7 detected in little cormorants may indicate the influence of the anoxic water, typical of a freshwater system densely covered by macrophytes. 5. These results indicate how both biomarkers offer complementary information in studies of feeding ecology, refining interpretations of trophic pathways which are usually based on FA or SIA alone. Comparisons of FA profiles and SIA among species also proved to be a reliable approach for inferring the diet of species for which information is scarce or contradictory, as is the case for the pheasant-tailed jacana.
Global change biology, 2014
The world's oceans have undergone significant ecological changes following European colonial expansion and associated industrialization. Seabirds are useful indicators of marine food web structure and can be used to track multidecadal environmental change, potentially reflecting long-term human impacts. We used stable isotope (δ(13) C, δ(15) N) analysis of feathers from glaucous-winged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long-term trends in gull abundance. Sampled feathers came from birds collected between 1860 and 2009 at nesting colonies in the Salish Sea, a transboundary marine system adjacent to Washington, USA and British Columbia, Canada. To determine whether temporal trends in stable isotope ratios might simply reflect changes to baseline environmental values, we also a...
Foraging habitat use by colonial waterbirds breeding in New York Harbor was examined to identify resources that were particularly important for the provisioning of young. Stable isotope values of carbon, nitrogen, and sulfur were measured in nestling waterbird feathers to determine the habitat type (ranging from marine to freshwater and anthropogenic) in which adults primarily foraged. Six species were investigated: Black-crowned Night-Herons (Nycticorax nycticorax), Great Egrets (Ardea alba), Glossy Ibises (Plegadis falcinellus), Double-crested Cormorants (Phalacrocorax auritus), Great Black-backed Gulls (Larus marinus), and Herring Gulls (L. argentatus). Waterbird populations exhibited both inter- and intra-specific variation in stable isotope values (P < 0.001), indicating variation in foraging habitat use among focal species across the estuary. Therefore, depending on the species-and region-specific conservation goal, management strategies would potentially need to target very different foraging habitats for protection and remediation. For instance, habitat use by Double-crested Cormorants closely reflected available habitat near nesting colonies, while Glossy Ibises used primarily freshwater resources at one colony and marine resources at another, despite the fact that both colonies were located in marine environments. Great Egrets and Double-crested Cormorants both showed significant regional variation in isotopic niche size, and both species of gulls (considered to be generalist scavengers) were found to have isotopic niche sizes reflecting a specialist diet. Stable isotope analysis of nestling feathers provided novel information about the foraging resources that were most important to waterbirds in regions across the harbor.