Vesper sparrow (Pooecetes gramineus affinis) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
Vesper Sparrows are grassland birds, preferring dry, open areas with short, sparse grass or herbaceous cover (Reed 1986; Dechanteet al. 2001; Campbell et al. 2001). Structural diversity is important; taller vegetation such as scattered shrubs or trees at the edge of grasslands is used for cover and for singing perches while areas with shorter vegetation are used for foraging (Davis and Duncan 1999). In western Washington, Rogers (2000) determined that foraging Vesper Sparrows used sites with a mean cover of 32% bare ground, with the remainder grasses and forbs. Fence posts, wire fences and other man-made structures are also used for singing perches (Beauchesne 2002b).
Several studies indicate that Vesper Sparrows avoid permanent pasture and hayfields (see Kantrud 1981; Prescott et al. 1995 in Jones and Cornely 2002; Campbell et al. 2001). This was consistent with results from inventory work on southeastern Vancouver Island where breeding territories were found in areas adjacent to, but not within, areas used for hay production (Beauchesne 2002a, 2003, 2004). Vesper Sparrows appear to prefer grassland away from urban edges (Bock et al. 1999; Jones and Bock 2002). Size of habitat patch may also be important (Kershner and Bollinger 1996; Rogers 2000). For example, in Washington Coastal Vesper Sparrows are currently found in large prairie areas, but not in small patches of similar habitat (Scott Pearson, pers. comm.). In eastern Oregon, however, they have been recorded breeding in areas of <4 ha (Jones and Cornely 2002) and on Vancouver Island, the extant population occurs in an area of suitable habitat of approximately 10 ha (Beauchesne 2002a).
On Vancouver Island, the plant community at the known breeding site includes both native and non-native flora. Birds were frequently seen using clumps of Scotch broom, Cytisus scoparius, for singing perches and escape cover. They foraged on the ground in the adjacent open areas with gravely soil and sparse forb and grass cover (Beauchesne 2002a, 2003, 2004).
Trends
All Subspecies
Across the range of the Vesper Sparrow, grassland habitats have been altered since the arrival of Europeans. In many areas, Vesper Sparrow habitat has declined in quality and quantity with development (urban and industrial) and modified farm practices (e.g., earlier and more frequent mowing; larger crop fields with subsequent reduction of hedgerows: Jones and Cornely 2002; Altman 2003).
Coastal Vesper Sparrow
Before European colonization, habitat for the Coastal Vesper Sparrow in British Columbia was likely restricted to xeric, sparsely vegetated areas within grassland and Garry oak ecosystems, especially those recently burned by First Nations peoples. A theoretical map of habitat types in existence prior to European colonization (1859) in the lower Fraser River valley shows “grassland” habitat along the edges of the Fraser River, Sumas Lake, and on the Fraser River delta (T. Lea pers. comm.). That grassland was extensive in places, as described by Lt. Charles Wilson, during the 49th Parallel Survey, 1858-1862. "The prairie runs down to the bank of the Chilukweyuk from which we are about 2 miles distant, the view from the camp is superb, the prairie in front with its beautiful waving grass and belts of poplar, willow, ash and maple in the foreground” (Chilliwack Museum 2002). Although grassland type was not further specified, it is possible that some of that grassland was short-grass prairie which could have provided habitat for Vesper Sparrows.
On Vancouver Island, Governor Douglas wrote of “walking across open prairie for 6 miles behind Fort Victoria”, an indication that there were large areas of open grassland in the region. Maps of historic open plant communities in the Victoria region show that grassland and Garry oak savannahs were extensive (T. Lea pers. comm.), even though much of the information was compiled from surveys conducted 30 years or more after Governor Douglas banned grassland burning by First Nations so considerable in-growth by Garry oak and Douglas fir would have already begun (Lutz 1995; Turner 1999). Remnants of the large expanse of open prairie can be found at Beacon Hill Park, Victoria and Trial Island Ecological Reserve, Victoria. Although some of these areas appear to be suitable for Vesper Sparrows, they are currently very small.
European settlers probably initially increased available terrestrial habitat in southwestern British Columbia through clearing of forests and draining of wetlands for agricultural purposes. However, those habitat areas have subsequently declined in size and quality through urbanization and intensification of agriculture. Agricultural land in the region continues to be converted to housing, golf courses, commercial developments, or industrial greenhouses that preclude use by the Vesper Sparrow (Dawe et al. 2001). At the same time almost all of the natural habitat options have also been lost or drastically altered, so that naturally occurring alternative habitats exist only as tiny remnants.
Decades of fire suppression have led to infilling of grassland and oak meadow habitat and have prevented the creation of new open areas. Most of the region has been modified for residential or agricultural purposes with dramatic changes to topsoil and water regimes and subsequent alteration to vegetation structure. In addition, alien species invasion is further altering vegetation structure in the remaining habitat (i.e., Scotch Broom and exotic tall grasses are replacing native short grasses and forbs). The reduction of naturally occurring terrestrial habitats in the region over the past 150 years, due to human modifications, has been estimated at 80% (Ward et al. 1998) and Fuchs (2001) estimates that Garry oak and associated ecosystems in British Columbia have declined in area by 95% (Fuchs 2001).
The Nanaimo Airport is currently one of the few sites in the region with a relatively large area of suitable habitat (Beauchesne 2002a; 2003). Topsoil removal for runway development has mimicked a natural erosion event, leaving behind a gravel base that has limited plant growth. Elsewhere, it has been noted that airports represent some of the largest remaining open grasslands and, if well managed, may provide critical refuges for many grassland species (Kershner and Bollinger 1996).
Elsewhere, declining populations in Washington and Oregon are linked with habitat loss (Rogers 2000; Altman 2003). Prairie habitat in western Washington has declined an estimated 98% since the arrival of European settlers, with prairies being converted to urban or unsuitable agricultural areas, returning to forest because of fire suppression, or being invaded by exotic plants (Crawford and Hall 1997; Smith et al. 1997; Rogers 2000). The Willamette Valley in western Oregon still supports a remnant population of Coastal Vesper Sparrows, but has undergone dramatic habitat changes since the arrival of Europeans (Altman 2003).
Protection/ownership
The only known breeding site for Coastal Vesper Sparrow on southeastern Vancouver Island is on the grounds of the Nanaimo Airport. This independent airport is owned and managed by the Nanaimo Airport Commission (NAC 2001, 2002, 2005). The primary consideration for vegetation management at the site is compliance with Federal Aviation Authority (FAA) regulations (B. Clark pers. comm.).
Other historic breeding sites on Vancouver Island are on private agricultural land, management of which is typically at the discretion of the individual landowner. There is also possibly some suitable habitat within regional parks and other protected areas, but the amount available has not been assessed. Given the development pressures on southeastern Vancouver Island and the lower mainland, it is unlikely that a substantial amount of additional suitable habitat will be created in the future (Dawe et al. 2001). Therefore stewardship of existing habitat is very important.
Recognizing the importance of the Nanaimo Airport to the survival of the Coastal Vesper Sparrow in Canada, the Vertebrates Recovery Implementation Group (RIG) of the Garry Oak Ecosystems Recovery Team (GOERT) adopted a formal Stewardship Agreement with the Nanaimo Airport (Beauchesne 2002c). Although grassland conservation has not been the primary goal of this commercial enterprise, runway maintenance to date has apparently been compatible with Vesper Sparrow breeding habitat requirements (Beauchesne 2002b). The Vertebrates RIG is now working with airport management, within the scope of Transport Canada regulations and other over-riding policies, to protect and further enhance the Vesper Sparrow breeding site. The agreement, covering issues such as the timing of mowing, timing and location of pesticide applications, control of invasive species and other vegetation management issues, has been in place from 2003 and is expected to continue in the future (Beauchesne 2002c).
However, further development of the airport grounds could threaten continued persistence of this subspecies in the region. The Airport Commission’s Vision Statement indicates a commitment to both “aggressively pursue development opportunities, and exercise responsible environmental stewardship” (NAC 2001). The airport has a mandate to “generate and participate in economic development projects intended to expand air transportation facilities and to generate economic activity in all areas compatible with air transportation” (NAC 2005). Consequently the Stewardship Agreement includes a clause accepting that the airport may develop the area occupied by Vesper Sparrows, should an opportunity arise to generate economic activity (Beauchesne 2002c). Examples of land use options that have recently been entertained for the area are: storage of lumber, storage of heavy equipment, and development of more hangar sites, none of which are likely compatible with Vesper Sparrow breeding habitat requirements. Likewise, a modification of the runway maintenance program could be detrimental to Vesper Sparrow breeding habitat. Plans are currently being developed to upgrade the radar system at the airport, which in turn would require wider runway clearance (B. Clark pers. comm.). The ensuing mowing requirements would impact the Vesper Sparrow breeding site.
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