Craig E. Hebert

Feather stable isotopes in western North American waterfowl: spatial patterns, underlying factors, and management applications

Abstract Text.Knowledge of the natal origins of individual birds could provide valuable information for waterfowl conservation and harvest management programs. We used stable isotopes to differentiate birds from major western North America production areas, thereby providing a means of elucidating the natal origins of waterfowl. We used a multi-isotope approach (δ34S, δ2H, δ13C, δ15N) to determine if ducks originating from different geographic areas had unambiguous multi-isotopic signatures. During 1999–2001 we took secondary feathers from prefledged mallard (Anas platyrhynchos) and northern pintail (A. acuta) ducklings from 52 sites in western North America (n = 284). Ducklings from Alaska, northern Canada (YT, NWT), the Prairies (AB, SK, MB, MT, ND, SD), and California could be distinguished based upon their feather isotope values. Geographic patterns in feather isotopes were related to natural gradients produced by biogeochemical cycles and anthropogenic factors such as agrochemical usage. Stable isotopes are naturally occurring markers that may be a useful tool in the effective management of waterfowl populations.

UNIQUE ISLAND HABITATS MAY BE THREATENED BY DOUBLE-CRESTED CORMORANTS

Abstract Double-crested cormorant (Phalacrocorax auritus) populations on the Great Lakes expanded greatly during the past 2 decades. On Lake Erie, the number of breeding cormorants increased from 174 birds (87 nests) in 1979 to 26,542 (13,271 nests) in 2000. In 2000, 81% of the breeding population was on 2 western-basin islands (East Sister and Middle Islands). The plant communities on these islands represent some of the last remnants of Carolinian vegetation in Canada. Our study is the first to quantitatively assess the relationship between the distribution of nesting cormorants and forest health. On East Sister Island, 2 measures of forest cover were obtained using infrared aerial photographs and ground-based measurements of leaf area index. These measures of forest cover were correlated (rs = 0.70, P < 0.001), which validated the use of remotely sensed data to assess forest cover. Cormorant nest density was negatively correlated with tree cover on both East Sister and Middle Islands. Temporal comparisons of Middle Island data indicated a reduction in tree cover from 1995 to 2001, and these reductions coincided with a large increase in the islands cormorant population. Although correlational in nature, our results suggest that cormorants may be detrimentally affecting island forests.

WINTER SEVERITY AFFECTS MIGRATION AND CONTAMINANT ACCUMULATION IN NORTHERN GREAT LAKES HERRING GULLS

Herring Gull band returns were analyzed from 1962 to 1995. Winter severity was found to affect the winter distribution of Herring Gulls banded as flightless chicks on colonies in northern Lake Huron and northern Lake Michigan. The effects of winter severity were most pronounced in adults, followed by immatures. Little response was observed in juveniles. In adults, the proportion of band returns from southerly locations increased in response to increased winter severity. In general, concentrations of organochlorine contaminants in Herring Gull eggs collected annually from northern Great Lakes colonies increased with winter severity. However, the significance of the relationship between winter severity and organochlorine concentration was compound and colony specific. This probably reflected intercolony differences in winter migration patterns with concomitant differences in contaminant exposure during the overwintering period. With increased winter severity, gulls migrated to more contaminated southerly Great Lakes locations. After spending the winter in these areas the birds returned to their breeding colonies, transferring contaminants to their eggs. The degree to which Herring Gull eggs laid on colonies located in the northern Great Lakes reflect local contaminant bioavailability will be affected by winter severity and overwinter migration patterns.

Comprehensive re-analysis of archived herring gull eggs reconstructs historical temporal trends in chlorinated hydrocarbon contamination in Lake Ontario and Green Bay, Lake Michigan, 1971–1982

Herring gull egg homogenates collected between 1971 and 1982 from a colony in central Lake Ontario (Scotch Bonnet Island) and from a colony in central Green Bay, Lake Michigan (Big Sister Island) were archived in the Canadian Wildlife Service Specimen Bank. Pooled samples (N = 10) were exhaustively analyzed in 1993 for a wide range of individual chlorinated hydrocarbon contaminant (CHC) compounds: DDT, mirex and chlordane compounds and metabolites, chlorobenzenes (CBzs), dieldrin, chlorostyrenes (CSs), hexachlorocyclohexanes (HCHs), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), and 87 PCB congeners, including the TCDD-like non-ortho and mono-ortho congeners. PCBs and DDTs were the dominant residues in eggs from both Lake Ontario (31-242 mg kg(-1) and 9-64 mg kg(-1)) and Green Bay (34-133 mg kg(-1) and 14-91 mg kg(-1)). SigmaPCBs declined by a factor of 4-5 and DDTs a factor of 4-7 at both colonies between 1971 and 1982. Lake Ontario eggs had significantly higher residues of 2,3,7,8-TCDD (0.2-2.0 microg kg(-1)), HCBz (0.1-4.7 mg kg(-1)), OCS (0.03-0.45 mg kg(-1)), three HpCSs (0.13-0.97 mg kg(-1)), mirex and mirex photodegradation products (2.1-9.2 mg kg(-1)) than Green Bay eggs. HCBz levels in Lake Ontario eggs declined a factor of 40, TCDD and chlorostyrenes a factor of 8-10, and mirex a factor of 4 between 1971-1978. Green Bay eggs had slightly higher levels of chlordane-related compounds, dieldrin and beta-HCH than Lake Ontario eggs. There were no consistent or strong trends in residue levels of these pesticides, PCDDs (except TCDD) and PCDFs in either lake, indicating that rates of input and removal of these CHCs in the lakes were much closer in the early 1970s than was the case for the other compounds.

Historical Changes in PCB Patterns in Lake Ontario and Green Bay, Lake Michigan, 1971 to 1982, from Herring Gull Egg Monitoring Data

Patterns of PCB congener bioaccumulation were examined in archived herring gull (Larus argentatus) eggs collected from Big Sister Island in Green Bay, Lake Michigan, and Scotch Bonnet Island in Lake Ontario from 1971 to 1982 as part of the Canadian Wildlife Services Great Lakes Herring Gull Monitoring Program. Concentrations of 97 PCB congeners were measured. From 1971 to 1982, ecological half-lives of most congeners, particularly the tri- through hexachlorobiphenyls, were greater in eggs from Green Bay than Lake Ontario. Comparing sum PCB levels in eggs collected in 1971 and 1982, concentrations declined 80% at Scotch Bonnet Island and 74% at Big Sister Island. PCB congener patterns were different in eggs from the two colonies. Principal components analysis showed that inter-site differences in congener patterns became more apparent after 1976. This indicated that regional PCB sources were the most influential in determining patterns of biologically-available PCBs during the 1971 to 1982 period in these two lakes, via recycling of historical PCBs from sediments or gradually decreasing loading. Trend analysis of selected congeners specific to Aroclors 1242, 1254, and 1260 revealed that the rapid decline of less chlorinated congeners, observed from 1971 to 1976 in Lake Ontario, was explained by a decrease in loading of Aroclor 1242 to the lake. At both colonies, ecological half life of the congeners was significantly (p < 0.001) correlated with log Kow and with –log HLC. Changes in PCB composition, after 1976 in Lake Ontario and from 1971 to 1982 in Green Bay, could be explained by differences in the physical behavior of individual congeners affecting removal by volatilization and sedimentation.

STABLE ISOTOPES PROVIDE EVIDENCE FOR POOR NORTHERN PINTAIL PRODUCTION ON THE CANADIAN PRAIRIES

Abstract Concerns have been raised regarding declines in western North American northern pintail (Anas acuta L.) populations over the past 30 years. Elucidating the natal origins of pintails and identifying production areas of pintails are important steps in determining the cause of the observed declines. Here, we used stable isotope (sulphur, hydrogen, carbon, nitrogen) featherprints to determine the geographic origins of northern pintail ducks shot by hunters in southern Alberta and Saskatchewan, Canada. Based on the best data available for inferring the distribution of breeding pintails, the proportion of hatch-year pintails originating from Prairie regions was smaller than expected. Our results suggest that production of northern pintails on the Canadian Prairies may be significantly lower than predicted by the number of breeding birds and may be related to human-induced reductions in nest success as a result of agricultural practices.

The Relevance of Seabird Ecology to Great Lakes Management

Abstract Seabirds are an integral part of Great Lakes ecosystems. However, most species are of no economic importance to humans and, therefore, they receive little direct management attention. Because many species of seabirds on the Great Lakes rely on fish as their primary food, factors that alter fish availability will also affect seabird populations. This paper examines how management practices may indirectly affect Great Lakes seabirds leading to changes in population sizes, diet composition, and destruction of breeding habitat. Consideration of the impacts of management actions on non-target groups, such as seabirds, will require the application of an ecosystem approach to management. Although the ecosystem approach philosophy has been widely accepted from a theoretical perspective, little tangible evidence exists that it has been routinely applied.

White Pekin Ducks (Anas platyrhynchos) as Monitors of Organochlorine and Metal Contamination in the Great Lakes

Utilizing domestic birds as biomonitors may provide vital information regarding the risk to migratory waterfowl posed by contaminated wetlands. Data collected from domestic waterfowl might also allow scientists to address the public health implications of feral waterfowl consumption by humans. In this study, the white Pekin duck (Anas platyrhynchos) was evaluated as an indicator of environmental contamination in the lower Great Lakes during 1986. These birds rapidly accumulated organochlorine and heavy metal contaminants, sometimes to high levels. Intersite differences in their contaminant burdens reflected known geographic differences in contaminant sources. There were, however, some difficulties associated with using white Pekin ducks as biomonitors, most notably their high rate of disappearance after release. This reflected their vulnerability to predation and poaching but at one of the sites, Windermere Basin in Hamilton Harbour, lead poisoning may also have been a factor contributing to their disappearance.

Assessing Temporal Trends in Contaminants from Long-term Avian Monitoring Programs: The Influence of Sampling Frequency

The effect of sampling frequency on the detection of statistically significant temporal trends in egg contaminant levels was examined using data from the Great Lakes Herring Gull Monitoring Program. Decreased identification of statistically significant trends was apparent in the sampling regimes where samples were collected less frequently. When statistically significant declines were observed, sampling at two and four year intervals resulted in the trend being identified later than with annual monitoring. The design of monitoring programs must balance costs and data quality. Programs should ensure that the data collected are adequate to address critical questions.

Genetic Variation in Mitochondrial DNA of North American Herring Gulls, Larus argentatus

The herring gull (Larus argentatus), which is one of the most abundant gulls in temperate North America, is used as an important bioindicator species, but little is known about its patterns of genetic variation. This study examines DNA sequence diversity in the cytochrome b gene of mitochondrial DNA (mtDNA) from herring gull colonies in the Great Lakes basin and from a site in the Maritimes. A 307-bp fragment of the gene was analyzed using a rapid mutation screening procedure coupling directed termination PCR (DT-PCR) with single-stranded conformation polymorphism (SSCP). Seven mtDNA haplotypes were revealed in 224 specimens with a common haplotype dominating all populations. Direct sequencing of a 1063-bp fragment of the cytochrome b gene identified 8 additional haplotypes, but the sequence divergence among all 15 haplotypes was very low (average 0.24%). These data suggest that herring gulls experienced a bottleneck during the last glaciation that is now reflected in their low levels of genetic divergence. The geographic distribution of mtDNA haplotypes indicates that gene flow among herring gull populations is sufficient to ensure genetic homogeneity in the Great Lakes, but insufficient to homogenize genetic variation between the Great Lakes and the Maritimes. Meanwhile, a comparison analysis of frozen egg specimens suggests a possible shift in the genetic composition of the Great Lakes populations over the last 15 years.