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Water birds
State of Colonial Nesting Aquatic Bird Populations
Outlook
The monitoring of the state of colonial aquatic bird populations shows that Herring Gulls eggs from the Great Lakes and Upper St. Lawrence River contained far higher levels of contaminants than those from the St. Lawrence River, estuary and gulf, downstream of Montreal; cormorant eggs, where available, also usually follow this pattern, although differences are of less importance. These higher levels of contaminants may be due to several factors. Obviously, the Great Lakes are a much more “closed” system. The retention (or exchange) time of water in the lakes is in the order of decades. This longer retention time means that birds are perhaps exposed to the same contaminant regime for extended periods of time, even if the input has been reduced for many years. On the contrary, in the St. Lawrence River, the water flows rapidly and contaminants are transported to the estuary, the Gulf and the Atlantic Ocean, where dilution allows a reduction in concentrations. In addition, the Herring Gull is a permanent resident in the Great Lakes, but a migratory bird in the St. Lawrence River, thus influencing the accumulation of contaminants.
Among the Canadian Wildlife Service contaminants monitoring programs, levels of contamination in aquatic birds appear to follow this decreasing progression: Great Lakes > St. Lawrence estuary and Gulf > Bay of Fundy in Atlantic region > Georgia Straight in Pacific region > the Arctic. The contamination levels observed today in the Great Lakes and St. Lawrence River are generally lower than concentrations considered harmful for survival, reproduction and health of birds, although the highest levels measured in the Great Lakes are still of concern.
Thirty years ago, the effects of contaminants on aquatic birds were very obvious and had dramatic population level effects, such as eggshell breakage due to eggshell thinning, and its effects on reproductive success, such as gross congenital deformities, caused population declines. Impacts of contaminants now are much more subtle and often at the physiological level. They involve suppression of the immune system, possible feminization of male birds, enzyme induction, hormone suppression, disruption of endocrine system, etc. The impacts of these physiological effects on population levels of these birds are not well known. Population levels of most of the indicator species studied appear strong or stable. However, it is not known, for instance, the possible impacts of these physiological stresses on the life span of birds and on populations.
It is thus important to maintain ongoing monitoring programs, not only to know which contaminants are increasing or decreasing, but also to document the effects these contaminants may have on the health of bird populations and ecosystems.
This integration exercise offers a new and interesting perspective on the evaluation of the contamination of the Great Lakes-St. Lawrence ecosystem. In order to benefit from better knowledge of the state of the populations of colonial aquatic birds and of the changes that may affect them, and for the management of the Great Lakes-St. Lawrence River basin, more efforts should be devoted to the co-ordination of integrated monitoring programs, the selection of common indicator species and a better spatial and temporal sampling coverage in the entire basin.
To Learn More
Morris, R.D., Weseloh, D.V., and Shutt, J.L. 2003. Distribution and abundance of nesting pairs of Herring Gulls (Larus argentatus) on the North American Great Lakes, 1976 to 2000. J. Great Lakes Res. 29:400-426.
Noble, D. 1990. Contaminants in Canadian Seabirds. State of the Environment report. Canadian Wildlife Service and Environment Canada, Ottawa, ON. Report EDE no. 90-2.
Norstrom, R.J., Simon, M., Moisey, J., Wakeford, B., and Weseloh, D.V.C. 2002. Geographical distribution (2000) and temporal trends (1981-2000) of brominated diphenyl ethers in Great Lakes Herring Gull eggs. Environ. Sci. Technol. 36:4783-4789.
Rail, J.F., Chapdelaine, G., Brousseau, P., and Savard, J.P.L. 1996. Utilisation des oiseaux marins comme bioindicateurs de l'écosystème marin de l'estuaire et du golfe Saint-Laurent. Service canadien de la faune, région du Québec, et Environnement Canada, Sainte-Foy, QC. Série de rapports techniques No 254, ii + 113 p.
Weseloh, D.V.C., Pekari k, C., Havelka,T., Barrett, G., and Reid, J. 2002. Population trends and colony locations of Double-crested Cormorants in the Canadian Great Lakes and immediately adjacent areas, 1990-2000: a manager’s guide. J. Great Lakes Res. 28:125-144.
Louise Champoux Chip Weseloh
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Date modified: 2008/05/01 – Important Notices
