D. Vaughn Weseloh

Organochlorine contaminants in eggs of Common Terns from the Canadian Great Lakes, 1981.

To determine if contaminant levels in Common Terns had changed over the last decade, we collected and analyzed eggs from four nesting colonies on the three lower Great Lakes during 1981. DDE and PCBs were detected in every egg from the four colonies. Dieldrin, mirex and trans-nonachlor were detected in more than 45% of the eggs. Seven other organochlorine contaminants (DDD, DDT, hexachlorobenzene, oxychlordane, cis-chlordane, cis-nonachlor and toxaphene) were detected in less than 25% of the eggs. Eggs from the Lake Ontario colony were generally the most heavily contaminated. Comparisons of DDE and PCB data with earlier studies of Common Terns indicated that contaminant levels in eggs from the four sampled colonies, or nearby sites, have decreased by up to 80-90% from 1969-1973 to 1981. Interspecies comparisons showed that Common Tern eggs have lower organochlorine residue levels than eggs of Caspian Terns or Herring Gulls. Dietary variation and migratory status are possible explanations for the differences in residue levels among species. Eggshell thickness, log-PCBs, and log-DDE were not significantly intercorrelated. Elevated contaminant levels in the early 1970s might be at least partly responsible for the decline of the Great Lakes Common Tern population over the past decade. Stabilization of population numbers during the early 1980s suggests that organochlorine pollution levels have been reduced to a point where they are no longer an important factor in the population dynamics of this species on the Great Lakes.

Accumulation of organic contaminants in sentinel mallards utilizing confined disposal facilities at Hamilton Harbour, Lake Ontario, Canada

Organochlorine analysis was performed on adult and juvenile farm-raised mallards (Anas platyrhynchos) released and collected at three experimental sites in southern Ontario: Hamilton Harbour Confined Disposal Facility (CDF); Winona Sewage Lagoons (SL); and Big Creek Marsh, Canada. Collections were scheduled at 10, 30, and 70 days after release. Hamilton Harbour CDF and Winona SL are known to be contaminated whereas Big Creek Marsh is a relatively clean, natural site. All sites are important resting and feeding areas for migratory and resident waterfowl. Breast muscle concentrations of polychlorobiphenyls (PCBs) in ducks collected 10 days after release (160.8 μg/kg, wet wt) at Hamilton Harbour CDF were more than 5300 times greater than day “0” birds (0.03 μg/kg). All ducks collected from Hamilton Harbour CDF had PCB concentrations exceeding Health and Welfare Canada and United States Food and Drug Administration (FDA) guidelines for edible poultry. Concentrations of DDE (216.9 μg/kg), hexachlorobenzene (0.9 μg/kg), dieldrin (1.9 μg/kg), and 1,2,4,5,-tetrachlorobenzene (24.9 μg/kg) were significantly elevated in ducks utilizing Winona SL. Concentrations of 1,2,3,4-tetrachlorobenzene, mirex, and photomirex were elevated at one or more of the sites. Ducks from Big Creek Marsh had lower contaminant concentrations than ducks from the other study sites. It is not clear whether bioaccumulation of organochlorines at these sites would pose a potential hazard to migratory and resident mallards; however, other duck species such as diving ducks that have more contact with sediments and sediment-derived foods would probably be at much higher risk.

Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999

ABSTRACT Canadian and US federal wildlife agencies completed three surveys (1976–1980, 1989–1991, and 1997–2000) to census colonial waterbirds breeding on the Great Lakes. We here summarize and comment on nest numbers and colony site distribution of common terns (Sterna hirundo) and Caspian terns (Hydroprogne caspia). Common terns are in serious trouble on the Great Lakes. Numbers declined with substantial losses in nests (-19.1%) and colony sites (-23.2%) between the first and third censuses. An increase in numbers at US sites (+ 26.6%) did not compensate for losses (-33.1%) at Canadian sites. Caspian terns increased in nest numbers (+ 65.9%) and colony sites (+ 50.0%) over the same period. The increase at US sites (136.5%) was greater than at Canadian sites (11.5%). Most (70.7%, n = 186) common tern sites had nests during only one census; 17 sites (6.5%) had nests during all censuses. In contrast, 9 of 33 (27.2%) Caspian tern sites had nests during all censuses and contained a majority of nests (50–82%) in each census. Pairs of both species nested on natural substrates across the Great Lakes. Common terns nested mostly on artificial (human-constructed) substrates on the lower Great Lakes. We identify site characteristics that may have contributed to long-term (three census) occupancy by common terns (small size, artificial substrates, absence of ring-billed gulls) and Caspian terns (natural substrates on large, remote islands). We suggest an urgent need for protection and conservation of common tern colonies and identify specific priority sites for implementation of management protocols.

Distribution and Abundance of Nesting Pairs of Herring Gulls (Larus argentatus) on the North American Great Lakes, 1976 to 2000

During the past three decades, Canadian and U.S. federal wildlife agencies completed three major surveys (1976–1980; 1989–1990; 1998–2000) to census seven species of colonially nesting waterbirds breeding on the Great Lakes. We summarize and comment on distribution and abundance of herring gulls (Larus argentatus), the most widely distributed of the species. Lake Huron consistently supported the highest number of nesting pairs, followed by Lakes Superior, Michigan, Erie, and Ontario. The pattern on four lakes was an increase in numbers between the first and second censuses, then a decrease between the second and third census. Numbers on Lake Huron declined between each census. Patterns may be food based although corroborative data are lacking. At colonies censused in all periods (1,025 sites representing 80–89% of all pairs counted), the population increased from 63,618 to 69,975 pairs (first to second census), then declined to 59,590 pairs (last census). The low average annual rate of change (–0.3%) indicates that the Great Lakes herring gull population was stable over three decades at around 60,000 breeding pairs. We identify 20 sites across the Great Lakes where large changes (> 50% between two successive periods) were recorded, and suggest that inter-colony movements could explain changes in numbers among 11 of these sites on Lakes Huron and Michigan. We offer two examples of research protocols that use annual data collection from a limited number of colony sites to more directly address the causes of numerical and distributional changes in numbers of nesting pairs.

Population Trends of Ring-billed Gulls Breeding on the North American Great Lakes, 1976 to 2009

Abstract. After near extirpation in the early 20th century, Ring-billed Gulls (Larus delawarensis) are currently (2009) the most abundant colonial waterbird nesting on the Great Lakes. Nest count data are reported from four decadal censuses (1976–2009) conducted by the Canadian Wildlife Service and the U.S. Fish and Wildlife Service. Numbers increased from 305,790 nests (1976–80) to a peak of 718,887 nests (1989–90), then decreased to 652,664 (1997–2000) and to 585,984 nests (2007–09). Changes varied spatially after the second census with greatest losses (-38.6%) at North Channel, Georgian Bay and northern Lake Huron colonies, and greatest gains (+324.2%) at Lake Michigan colonies. A total of 472 sites had nests in at least one census (Canada N = 319; U.S. N = 153). Eighteen (3.8%) colonies had >2,000 nests in all four censuses, and had 37.5–41.9% of all nests in each census. Site occupancy was fluid. A high proportion (56.8%, N = 268) of sites contained nests in only one of the four censuses, and few (N = 40, 8.5%) had nests in all censuses. Thirty-nine sites had >2,000 nests gains/losses between census periods; 14 (35.9%) were on urban/industrial lands with artificial substrates. Human management and predator activities at some colonies contributed to declines in nest numbers at these locations. Movement of breeding birds among colonies and changes in local food supply may have influenced changes in nest numbers elsewhere. Reasons for the overall nest losses across the Great Lakes after the second census are unknown.

The Ratio of DDE to PCB Concentrations in Great Lakes Herring Gull Eggs and its Use in Interpreting Contaminants Data

The ratio of DDE to PCB (DDE.PCB) concentrations was examined in herring gull (Larus argentatus) eggs collected from thirteen sites on the Great Lakes from 1979 to 1996. This ratio has been shown to have had a number of biological interpretations in the past and the data in this study have been used to test the validity of these interpretations. The findings suggest that the consistency of DDE:PCB over many years reflects the relative availability of DDT and PCB in different geographical areas and provides an indication of a birds general foraging ecology. The ratio can also be used as a reflection of the relative rates of increase or decrease of DDE and PCBs in food over time. A significant increase was found in the ratio in eggs sampled from sites on the upper Great Lakes and Lake Ontario during the study period. This is attributed to PCB levels decreasing faster than DDE levels at these sites. At Lake Erie and its two connecting channels, a significant increase was detected in the ratio but at a rate 56% or less than that found at other Great Lakes sites. This lower rate is attributed to DDE and PCB levels decreasing at high and equal rates. Similarities/differences in the fates of these contaminants among the Great Lakes would never have been realized upon an examination of individual contaminant levels alone. The ratio is valuable as a measure of the relative exposure of the two contaminants in non-migratory birds such as herring gulls. The use of the ratio as an indication of contamination movement through the food chain could not be assessed; the ratio cannot be used as a reflection of the interspecific differences in the accumulation and metabolism of the two contaminants. Similarities in the patterns of these ratios shown by eggs collected from sites in close proximity or within the same lake reinforce the fact that herring gulls are important as monitors of regional contaminant conditions.

Waterbird Surveys at Hamilton Harbour, Lake Ontario, 1985–1988

Waterbird surveys were conducted at Hamilton Harbour and Windermere Basin from 1985–88 to help assess current wildlife usage of Burlington Bay vis-a-vis the Remedial Action Plan (RAP) for Hamilton Harbour. A total of 43 and 32 waterbird species (not including shorebirds) was recorded at Hamilton Harbour and Windermere Basin, respectively. Generally, more species of loons and grebes and aquatic raptors such as osprey and bald eagle were found at Hamilton Harbour than at Windermere Basin. Species such as mallard and Canada goose which key into unnatural food sources at marinas and golf courses, and double-crested cormorants, associated with a growing colony, were present in large numbers at Hamilton Harbour. Large numbers of common mergansers congregated on the harbor in early winter before freeze-up. On average, waterbirds were found in greater numbers at Windermere Basin. The large numbers of scaup and dabbling ducks, such as black duck and mallard, present at Windermere Basin were attracted by the warm water, low disturbance, and abundant available food source. The ice-free conditions at Windermere Basin also attracted regionally rare wintering species such as northern pintail, northern shoveler, ruddy duck, and green-winged teal. Survey results were compared to unpublished survey data from Cootes Paradise and published results of the annual mid-winter waterfowl survey of western Lake Ontario. The importance of Hamilton Harbour and Windermere Basin to migratory waterbirds should be considered regarding future clean-up of Burlington Bay.