No abstract

Lake Ontario and St. Lawrence River (LOSL) wetland bird abundance and diversity are greatly influenced by lake and river hydrology. Our study used an interdisciplinary ecosystem approach, blending avian and plant ecology, ecohydraulic, statistical ecology and modelling to evaluate potential impacts of water level fluctuations on indicator species representative of wetland breeding bird assemblages in the entire LOSL freshwater system. Multi-year (2000Multi-year ( -2003 bird surveys captured bird distribution and density in wetland habitats under varying degrees of water inundation, depth and fluctuation. Analyses revealed strong associations between estimated breeding pair densities and plant communities, water depth, and degree of water level fluctuation during the breeding season for a suite of wetland bird species using marsh, wet meadow, shrub swamp and treed swamp habitats. These quantitative associations were used to develop wetland bird performance indicators for use in a LOSL water regulation review study. Several bird species also nest at or near the water surface and are thus vulnerable to nest flooding or stranding. Changes to the seasonal hydrology of Lake Ontario and St. Lawrence River that result in an increased frequency or magnitude of these nest failure events may have a significant impact on regional population sustainability. Long term nest record databases were analyzed to create nesting flooding and stranding probability equations based on water level increases and decreases during the breeding season. These species-specific nesting relationships were incorporated into a reproduction index.Many breeding bird species were strongly associated with specific wetland plant communities. Predicted habitat suitability, as measured by estimated breeding pair density, can also change significantly within a specific wetland plant community based solely on changes in water depth during the breeding season. Three indicator species, Black Tern, Least Bittern and Virginia Rail were selected as key environmental performance indicators for alternate regulation plan comparisons.Water regulation criteria should be such that the long term diversity and abundance of wetland plant communities and frequency of spring flooding in marsh habitats during breeding are not reduced. Magnitude and frequency of water level change during the nesting season (May-July) can also adversely impact the reproductive success of many wetland bird species. As such, regulation criteria that increase the seasonal magnitude and frequency of water level changes may be detrimental to the long term viability of certain regional breeding bird populations.

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Mercury exposure was examined in adults and nestlings of ospreys (Pandion haliaetus) from lakes, rivers, and hydroelectric reservoirs in northern Québec between 1989 and 1991 by assessing the amount of mercury transferred from fish to ospreys, which are voracious fish-eaters. The high mercury concentrations detected in adult feathers and tissues (feathers, blood, liver, kidneys, muscles, brain) of nestlings indicate an increase in mercury availability at recently constructed hydroelectric reservoirs (10-12 years for the La Grande-2 Reservoir). With mean total mercury levels of 37.3 mg/kg and 1.9 mg/kg in feathers (dry weight) and in blood (wet weight), respectively, contamination rates were, in both tissues, five times higher for chicks born near the La Grande Reservoirs (western sector) than in those reared in natural habitats. Furthermore, the mean quantity of total mercury in 40-day-old chicks reared near a reservoir was 10.5 mg, compared with to 1.6 mg for those reared in a natural environment. Modeling of mercury transfer from fish to osprey nestlings showed that the mercury level in chicks' blood provides a good estimate of mercury concentrations in ingested food. In addition, the relationship between mercury concentrations in the blood and that in feathers indicates that substantial biomagnification of mercury occurs from the ingested dose to the feathers. The intensity of this biomagnification varies with the age of the chicks and reaches a maximum value as the flight feathers start to form (at 20-25 days of age) declining thereafter until the bird is 45 days old and growth of those feathers is complete. Nevertheless, the mean number of young fledged on reservoirs where mercury exposure is greatest (>40 mg/kg of Hg in chicks' feathers) did not differ (1.6 +/- 0.7) from that observed elsewhere in built-up environments (1.9 +/- 0.7) or in natural habitats (2.0 +/- 0.7) (H = 4.39; p = 0.11). Storage of mercury in growing feathers (86% of all mercury in osprey) prevents accumulation in living tissues, thereby protecting the chick from related toxic effects. However, toxicological problems may arise after fledging. In particular, attention should be paid to postfledging survival before concluding that mercury exposure is insufficiently high in Osprey young reared at reservoirs.

Jobin, B., Boutin, C. and DesGranges, J.-L. 1997. Effects of agricultural practices on the flora of hedgerows and woodland edges in southern Quebec. Can. J. Plant Sci. 77: 293-299. The structure and distribution of herbaceous species were examined in cultivated fields and in adjacent habitats in light of herbicide use and tillage. The diversity and vegetation cover of the herbaceous layer of hedgerows and woodland edges were lower on sites at which herbicides had been sprayed in recent years, probably due to herbicide drift during application on adjacent fields. Herbicide use and tillage had an impact on the species composition of the cultivated fields: there was a higher proportion of annual and introduced species in cultivated fields subjected to herbicide use and tillage than in fields that were not regularly treated or tilled. The species that were found only in non-crop habitats were primarily native and perennials, few of which were weed species, whereas a high proportion of the species found only in cultivated fields were annual and introduced species, several of which were considered weeds.