Lindsay Ware, M.Sc. Graduate, University of Western Ontario
Dr. Scott Petrie, Long Point Waterfowl Executive
Dr. Robert Bailey, University of Western Ontario
Background and Objectives
The combined North American population of Greater and Lesser scaup has declined continually since the mid-1980’s. There is much concern regarding scaup populations because relatively little is known about their declining numbers, including the major causes and the relative rates of decline of the two species.
Greater Scaup are of particular conservation concern because their numbers represent only about 11% of the continental scaup population. In addition, the two scaup species are not distinguished from each other during major population surveys (e.g. the Waterfowl Breeding Population and Habitat Surveys and the Mid-Winter Waterfowl Survey). Therefore, Greater Scaup population estimates may not be accurate, and the status of this species is uncertain. Because greater scaup also represent a small portion of the North American scaup population, it is thought that declining numbers of lesser scaup are driving the decline in the combined scaup population. While this situation is plausible, it does not preclude the possibility that Greater Scaup have also declined substantially. If this is true, such a precipitous decline could be having a major impact on the Greater Scaup population.
Several hypotheses have been proposed to explain the North American scaup decline. One such hypothesis is that birds may be acquiring elevated contaminant burdens on wintering or staging areas, which might subsequently impair reproduction or have lethal or sub-lethal health effects. Testing this hypothesis is especially relevant in the lower Great Lakes, because high levels of contaminants have been found in these waters. In addition, there is a high risk of contaminants being transferred to scaup through the consumption of zebra and quagga mussels (hereafter Dreissenid mussels). On the lower Great Lakes, the major components of scaup diets have shifted from native gastropods to Dreissenid mussels. Unlike gastropods, Dreissenid mussels can filter large amounts of water, zooplankton, and phytoplankton, thus accumulating water- and pelagic-based contaminants into their tissues.
Scaup that stage or winter on the Great Lakes have been tested for several metals, trace elements, and organochlorine pesticides. However, selenium is the only contaminant that has been found in scaup from this area in elevated levels. Selenium is a naturally occurring semi-metallic trace element required by animals for normal body function. However, it can also occur as an environmental pollutant due to agricultural, industrial, and urban run-off. Elevated environmental selenium levels warrant concern because excessively high selenium burdens in aquatic birds has been associated with reproductive effects such as reduced breeding propensity, delayed egg laying, embryotoxicity, teratogenesis, and reduced offspring survival. Excess selenium can also produce chronic health effects such as weakness, lethargy, anorexia, muscle and spleen atrophy, absence of subcutaneous and visceral fat, enlarged liver, pancreas, and kidneys, sloughed or broken claws, bill abnormalities, feather loss, histologic lesions, and mortality. In addition, selenium has been found to have a negative effect on body condition of aquatic birds, specifically in scaup. Such effects prior to egg-laying may have implications for reproduction because negative relationships between body condition and reproduction have been established in some waterfowl.
Scaup staging on the Great Lakes are acquiring potentially unhealthy selenium burdens. Recent studies conducted on the lower Great Lakes have detected selenium levels high enough to potentially impact reproduction in 93% and 75% of spring staging greater and lesser scaup, respectively (see Long Point Waterfowl’s Scaup Contaminents project). This is of concern because numbers of wintering and staging scaup on the lower Great Lakes have greatly increased since the late 1980’s. This suggests that scaup are remaining on the lower Great Lakes for longer periods of time to take advantage of the readily available Dressenid mussels. Further, although both species of scaup stage in this area, only greater scaup consistently over-winter in large concentrations. In fact, the Canadian side of Lake Ontario alone supports large numbers of greater scaup throughout winter, approximately 11% of the continental greater scaup population. Prolonged feeding on Dreissenid mussels with high contaminant burdens throughout winter could cause health-related problems or impair subsequent reproduction or survival. Therefore, if selenium acquisition is impacting scaup that use the lower Great Lakes, it is plausible that impacts are greatest for greater scaup that spend the entire winter in the region.