Horned lark, strigata subspecies COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
Across their range, Horned Larks are birds of open areas with short, sparse vegetation. The habitat requirements of Eremophila alpestris strigata are similar to other subspecies. In British Columbia, habitats used include agricultural fields, airports, beaches, sand dunes, short-grass playing fields, road sides, and other areas with bare ground. Documented breeding habitat was restricted to short-grass fields in agricultural areas, airports, and estuaries; and to sparsely vegetated, sandy beaches along the lower Fraser River (Butler and Campbell 1987; Campbell et al. 1997).
A recent inventory of sensitive ecosystems on eastern Vancouver Island and the Gulf Islands showed that naturally occurring, sparsely vegetated ecosystems (i.e., sand dunes, gravel and sand spits, and inland cliffs and bluffs) are the rarest terrestrial ecosystem in that region. The total area of this habitat type was estimated to be 37.9 hectares (Ward et al. 1998), therefore, very little suitable natural habitat currently exists.
In Washington, the centre of Eremophila alpestris strigata breeding distribution is in the glacial outwash prairies of south Puget Sound. These prairies were remnant grasslands left over from the last ice age. The soils of these prairies are thin, have low nutrient levels, and drain rapidly; characteristics that help maintain the prairie grassland condition. Other breeding sites in Washington and Oregon include dredged spoil islands in rivers, on sandy coastal beaches, or in disturbed areas on military training bases (Rogers 2000).
The last known breeding site in British Columbia was at the Vancouver International Airport from 1981 (Butler and Campbell 1987) and the most recent indication of potential breeding was from the Nanaimo Airport on Vancouver Island (Beauchesne 2002). In the Puget Sound area of Washington, four of five known breeding sites are at active airports. Elsewhere, airports are known to provide some of the last habitat refuge for grassland species, including Horned Larks. However, in an investigation of nesting success at ten airports, researchers found productivity to be much lower than in other grassland situations evaluated (Kershner and Bollinger 1996). Their data suggest that airports may be population sinks, offsetting any conservation benefits. Most of the nest failure recorded at airports was accidental destruction due to mowing. Although mowing regimes may be modified in other land-use areas to accommodate nesting birds, airports are bound by Federal Aviation Authority standards to maintain vegetation heights; which inevitably involves some mowing during the breeding season.
Trends
The amount of suitable habitat for the Horned Lark, strigata subspecies in British Columbia is very small and has undoubtedly declined over the last few decades as urbanization and other development has occurred within its breeding range.
Although historic habitat availability data for British Columbia is incomplete, some inferences can be made. Before European colonization, habitat was likely restricted to sparsely-vegetated sites such as spits, beaches, and, possibly, 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 some habitat for Horned Lark, strigata subspecies Brooks (1917) refers to Horned Larks as “stragglers” in the area in the early 1900s, but they may have been breeding at an unknown location nearby (Rogers 2000).
The breeding of Eremophila alpestris strigata was not documented in the lower Fraser River valley prior to 1926 (Brooks and Swarth 1925). The first records for that region are from Chilliwack and Sumas in the late 1920s, with breeding confirmed in 1928 (Behle 1942). In 1925, Sumas Lake was drained, exposing 3,600 ha of lake bottom which was subsequently farmed. It is probably not a coincidence that Horned Larks, strigata subspecies began to appear in this area in 1926. The drained lake would have created large amounts of sparsely-vegetated habitat (i.e., the type of habitat used by nesting Horned Larks) a year or two after being drained. This pattern has been noted elsewhere; in Oregon, Horned Larks, strigata subspecies were inferred to move into land cleared for pasture (Gabrielson and Jewett 1940). It is likely that the draining of Sumas Lake provided suitable habitat for Eremophila alpestris strigata in the lower Fraser River valley. This population may have developed from pioneers, dispersing from further south or may have been an augmentation of a small population that already existed in the Sumas Prairie.
Farmland in the Chilliwack and Sumas areas probably continued to provide some suitable habitat over the next two or three decades. By the 1960s more intensive farming practices were introduced which have reduced the amount of suitable habitat to the point that almost none remains.
The quantity of suitable breeding habitat that historically existed on Vancouver Island and the Gulf Islands is unknown, but is assumed to be much greater than that available currently. The reduction of naturally occurring terrestrial habitats in the region over the past 150 years, due to human modifications, has been estimated at between 80% (Ward et al. 1998) and 95% (Fuchs 2001). Governor Douglas talks about “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 horned larks, they are very small.
On Vancouver Island and the lower mainland, sandy beach and dune habitats have been drastically altered since the arrival of Europeans and large scale timber extraction, leading to changes in the amount and type of woody material deposited on beaches. Formerly a large amount of woody material that ended up on beaches was from large trees undercut by rivers and streams. These relatively structurally complex pieces (e.g., trunks with root wads attached) did not roll and helped stabilize sand beach and dune systems. After the advent of widespread logging and booming of wood, much of the material deposited on beaches is of a considerably less complex nature. Trunks are limbed, and root wads are cut off. Informal surveys indicate that somewhere between 70 and 87% of the woody material on BC beaches has saw cut ends. This results in logs that act like “rolling pins” rather than dune stabilizing structures, considerably altering the dynamics of sandy beach and dune communities (E. Baron, Parks Canada pers. comm. fide D. Fraser); Maser and Sedell 1994). To illustrate the changes to beach habitat, Page (in prep) analysed air photos of sand dune habitats on southern Vancouver Island and found that, over a 40 year period (ending mid-1990s), sites lost between 21 and 50% of their open dune areas, grass and bryophyte areas declined from 6 to 52% and forest and shrub cover increased from 46 to 220%, changes that would impact a species that prefers open grass to forest. To further exacerbate the situation, many sparsely-vegetated spits and foreshore sites in the region have been used as building sites for residential or light industrial purposes and as such are no longer suitable for Eremophila alpestris strigata, or other grassland bird species (Dawe et al. 2001).
In summary, there was an historical increase in terrestrial habitat in southwestern British Columbia through clearing of forests and draining of wetlands for agricultural purposes, followed by a decline in those habitat areas 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 Horned Larks (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.
Elsewhere, declining populations in Washington are linked with habitat loss. Prairie habitat in western Washington has declined 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 (Smith et al. 1997; Rogers 2000).
Protection/ownership
A few former breeding sites are located within regional parks on Sea Island and Iona Island. Iona Beach Regional Park includes a few hectares of sand dune and spit habitat, but some of that habitat is impacted by an active log salvage operation. The Sea Island Conservation Area, adjacent to Vancouver International Airport and within the area formerly used by nesting Eremophila alpestris strigata, contains 140 ha of woodlands, wetlands, and old field habitat and is administered by Environment Canada. This area could contain suitable habitat but only if fields are mowed short. An unknown amount of old-field habitat occurs in Richmond’s Terra Nova Natural Area reserve, but its suitability as habitat for the Horned Larks is uncertain.
A small amount of potential habitat still remains on privately owned agricultural land. Other potential breeding habitat occurs at Vancouver International Airport, Boundary Bay Airport, Victoria International Airport, Nanaimo Airport, Abbotsford Airport, and Chilliwack Airport. None of these sites are managed to conserve habitat for Horned Larks.
In Washington and Oregon, there are no records of Eremophila alpestris strigata occurring on National Wildlife Refuges (USFWS 2002). Most of the remaining breeding habitat is on military reserves (Rogers 2000).
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