Native Plants As Habitat For Wildlife - Native Plant Society of ...

Loss and Degradation of Native Mixed-grass Prairie: Implications for Grassland
Bird Conservation in Saskatchewan
Steve Davis
Saskatchewan Wetland Conservation Corporation
Analyses of data from the North American Breeding Bird Survey indicate that grassland
bird populations are experiencing the steepest and most consistent declines of any avian
group. Widespread loss and degradation of prairie habitat have often been cited as the
primary factors responsible for these declines. Unfortunately, few studies of grassland
birds have been conducted in Prairie Canada despite the fact that 70% of grassland birds
are declining in Canada and that several endemic grassland bird species reach their
greatest abundance in this region. Here I summarize recent research in an attempt to
identify factors that may contribute to the decline of grassland birds in Canada.
Results from grassland bird surveys indicate cropland habitat is least attractive for all
species with the exception of the Horned Lark. Several species are often associated with
hayland and seeded pastures (e.g. Baird’s Sparrow), while other species are mostly
restricted to native pasture (e.g. Sprague’s Pipit). These results suggest that 1) the
conversion of native prairie to cropland has likely played a major role in the decline of
grassland birds and, 2) while forage crops provide habitat for some generalist species,
they do not provide habitat for grassland specialists.
Over-grazing is often cited as having a deleterious effect on grassland birds because of
drastic changes in vegetation structure, although some species are associated with heavily
grazed habitats. Indeed, some species are least abundant in heavily grazed pastures and
residual vegetation has been found to be the most important parameter in nest-site
selection models. However, the overall impact that grazing has on grassland bird
populations in Saskatchewan is unknown and may be relatively minor.
Breeding habitat may also be degraded through the process of fragmentation. The
increased edge habitat resulting from habitat fragmentation may cause the loss of species
that require interior habitats and increase the abundance of edge species, including
predators and brood parasitic Brown-headed Cowbirds. Indeed, my research indicates
that grassland specialists are more likely to occur on large pastures and cowbird
parasitism is inversely related to patch size. However, nest success and productivity of
grassland birds was as high or higher in small native pastures (≤ 65 ha) than in large
pastures (> 256 ha). The results of these studies support the contention that the
destruction and fragmentation of native grasslands has contributed to the decline of some
grassland bird species. Thus conservation of Saskatchewan’s native range should be the
province’s highest conservation priority for sustaining endemic grassland bird
populations.
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