The role of Wildlife Management Areas for the conservation of grassland birds in South-western Manitoba

Background/Question/Methods  

Grassland songbirds have undergone population declines at a higher rate than any other avifaunal group in North America. These declines have been associated with habitat loss of native prairie. In south-western Manitoba, Canada over 80% of native habitat has been replaced by cultivation. In this region, remaining grasslands are represented by a combination of native and non-native grasslands including Wildlife Management Areas (WMAs), land units designated by the Manitoba Wildlife Act to conserve native wildlife. While WMAs have obvious recreational value, little information is available about what habitat characteristics make WMAs valuable for conserving wildlife, particularly to grassland birds. We surveyed bird diversity and associated vegetation to determine how WMAs contribute to the conservation of grassland birds, and how different land uses affect species richness and abundance of prairie birds. Bird diversity and vegetation structure were evaluated on 227 plots within 38 prairie sites including 12 WMAs, 13 private lands and 13 Crown lands, which covered different management practices: idle, haying, continuously and rotationally grazing. Birds were classified as obligate grassland birds, facultative and non-grassland birds for data analysis.

Results/Conclusions

WMAs supported the lowest richness and abundance of obligate grassland birds. Similarly, idle sites had the lowest richness compared to continuously and rotationally grazed areas. Concurrently, idle areas provided the highest richness and abundance of non-grassland species. Abundance of two obligate species was affected by land management. Western Meadowlark (WEME) was less abundant on hayed and idle sites than continuously and rotationally grazed fields. Savannah Sparrow was more abundant on hayed fields than idle and rotationally grazed areas. Also, WEME showed the lowest abundance on WMAs. Vegetation height, density, and percentage of grass appear to explain differences on bird abundances. Management practices did not affect the richness and abundance of facultative grassland birds. However, abundances of Clay-coloured Sparrows were higher on WMAs than private lands, and higher on idle areas than hayed sites. Similarly, Brown-headed Cowbird was more abundant on idle sites compared to continuously and rotationally grazed fields. WMAs tend to exclude both grazing and haying, which may promote a higher woody vegetation encroachment and influence suitability of native habitat for grasslands specialists. Our results suggest that active management is required to maintain grassland habitat within WMAs. Some practices, however, such as haying can reduce the relative abundance of grassland birds, so management decisions must be made cautiously.