Restoring hydro-impacted wetlands for secretive marsh birds

Author: A. Westphal

The Columbia Basin is within the Pacific Flyway, a major north-south flight path from the Arctic to South America used by migratory birds. Electricity demand within BC is only expected to grow, and while hydroelectricity may offer improvements over carbon-heavy electricity production there is still a critical need to address the effects these projects have on vulnerable species and ecosystems. In this study, I considered how frequently wetlands would experience an altered hydrological regime due to water management project operations. I examined how this might influence the densities of five secretive marsh bird species found in the Columbia Basin: American bittern (Botaurus lentiginosus), American coot (Fulica americana), pied-billed grebe (Podilymbus podiceps), sora (Porzana carolina), and Virginia rail (Rallus limicola). These species were surveyed in two regions within British Columbia, Canada: the West Kootenay and the Columbia Wetlands. I then examined aspects of the wetland ecosystem by the frequency of water management impacts, focusing on the structural composition of major habitat types and vegetation communities. Finally, I used occupancy models to assess the important driving forces behind marsh bird occupancy. I used the results of this study to inform recommendations for supporting these bird populations and restoring their wetland environment.

In the West Kootenay surveys between 34 and 60 stations were surveyed for marsh birds each year, of which approximately 15% were always impacted by hydro development or water management operations (hydro rank 1), 20% were occasionally impacted (hydro rank 2), and 65% were never impacted. American coot, pied-billed grebe, sora, and Virginia rail occurred in higher densities at stations which were less frequently impacted by water management projects.
I found that wetland characteristics (Table 2) varied with the frequency of water management impacts and, to some extent, between regions. All wetland characteristics apart from tall vegetation differed significantly between hydro rankings in the West Kootenay (Table 7, Figure 4). Open water cover was highest at stations which are always impacted by water management operations; emergent and tall vegetation cover were both highest at stations which are occasionally impacted; and woody vegetation cover was highest at stations which are never impacted (Figure 4).
I used occupancy models to examine the presence of American coot, pied-billed grebe, sora, and Virginia rail in the West Kootenay and Columbia Wetlands. Detection of all four species was best modelled as a function of survey date in either linear or quadratic form. The final models of all four species highlighted open water, woody vegetation, and elevation as being important contributing factors for station occupancy, and three of the four species highlighted tall vegetation as well. Effect sizes are given on the logit-scale and suggest that elevation has the largest impact on marsh bird occupancy for all four species followed by woody vegetation cover for American coot, pied-billed grebe, and sora, and open water cover for Virginia rail.

In the West Kootenay surveys between 34 and 60 stations were surveyed for marsh birds each year, of which approximately 15% were always impacted by hydro development or water management operations (hydro rank 1), 20% were occasionally impacted (hydro rank 2), and 65% were never impacted. American coot, pied-billed grebe, sora, and Virginia rail occurred in higher densities at stations which were less frequently impacted by water management projects.
I found that wetland characteristics (Table 2) varied with the frequency of water management impacts and, to some extent, between regions. All wetland characteristics apart from tall vegetation differed significantly between hydro rankings in the West Kootenay (Table 7, Figure 4). Open water cover was highest at stations which are always impacted by water management operations; emergent and tall vegetation cover were both highest at stations which are occasionally impacted; and woody vegetation cover was highest at stations which are never impacted (Figure 4).
I used occupancy models to examine the presence of American coot, pied-billed grebe, sora, and Virginia rail in the West Kootenay and Columbia Wetlands. Detection of all four species was best modelled as a function of survey date in either linear or quadratic form. The final models of all four species highlighted open water, woody vegetation, and elevation as being important contributing factors for station occupancy, and three of the four species highlighted tall vegetation as well. Effect sizes are given on the logit-scale and suggest that elevation has the largest impact on marsh bird occupancy for all four species followed by woody vegetation cover for American coot, pied-billed grebe, and sora, and open water cover for Virginia rail.