Post-dam vegetation changes and small mammal populations in the Peace-Athabasca delta

Research aimed at monitoring wildlife populations is a useful way to estimate the impact and consequences of hydroelectric projects on northern deltas. Such studies could provide valuable insights on the potential effect of the drying of deltas in the context of global climate change. The Peace-Athabasca River Delta, one of the most extensive northern inland deltas in the western hemisphere, represents a unique site to study such effects. Construction of the Bennett Dam in 1968 has had serious effects on the delta's ecological integrity; the resulting lower water levels and colonization of grass meadow communities by willows and the movement of shorelines has affected wildlife distribution and population levels. A study was conducted to estimate the impact of the invasion of grass meadows by willows on small rodent populations in the delta. Live trapping grids were established at three sites. Population estimates were obtained by the minimum number known method and used to calculate biomass of small mammals in willow and meadow grids. Mean trapping estimates (MTEs) of adult meadow voles ranged from under 1 per hectare on willow grids to 28 per hectare on meadow grids. On willow grids only, MTEs for adult populations of deer mice, red-backed voles, and meadow jumping mice reached 6, 6, and less than 1 per hectare respectively. It is estimated that the development of grass meadows into willow shrublands over the next 20-40 y could result in a loss of over 50% of the biomass of small rodents present in 1976. This should have a negative effect on the foraging efficiency and productivity of secondary consumers such as weasel and owl. 109 refs., 16 figs., 29 tabs