Western screech-owl (Otus kennicottii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

The habitats in which Western Screech-owls are found are quite varied: forests, semi-open woodlands, and scrubland, as well as arroyos, mature mesquite, cactus deserts, and treed suburban and urban areas (Bent 1938, Johnsgard 1988, del Hoyo et al. 1996, Hardy et al. 1999, Cannings and Angell 2001). It is often found in riparian zones.

Within Canada and the northern US states, the owl is generally found in lower elevation forested or treed environments, but the forest type and proportion of coniferous to deciduous trees vary depending on location. It is not found at higher altitudes; the upper elevation at which O. k. macfarlanei  is found has been variously estimated at: 600 m altitude above sea level (asl) (BC interior, Campbell et al. 1990), 1,220 m asl (US interior, Bendire in Bent 1938), and 1,555 m asl (southwestern Idaho, Doremus, pers. comm., 2001). The coastal subspecies O. k. kennicottii has been described as occurring between the January isotherms of 2°C and –7°C, or up to 915 m in Oregon and near sea level in southern Alaska (Hekstra 1982).

Coastal Subspecies – Otus kennicottii kennicottii

The coastal subspecies, Otus k. kennicottii seems to be found in a relatively wide variety of forest types. Early reports of the species in southwestern BC and northwestern Washington describe the species as occurring in a mixture of wooded habitats often dominated by deciduous trees and sometimes in open woodlands or near agricultural areas (Bowles 1906, Bowles 1917, Munro 1925). Campbell et al. (1990) state that it prefers mixed deciduous/coniferous forests, often along lakeshores and streams, but that it is found in all woodland habitats.

In 2000, habitats and roost locations of ten Western Screech-owl sites outside of Victoria, BC were examined (Darling and Hobbs pers. comm., 2001). Owls were found in mixed coniferous-deciduous forests, where the eight most common species in descending order of abundance (based on stem number) were: Douglas-fir (Pseudotsuga menziesii), Arbutus (Arbutus menziesii), Western Redcedar (Thuja plicata), Grand Fir (Abies grandis), Red Alder (Alnus rubra), Broadleaf Maple (Acer macrophyllum), Garry Oak (Quercus garryana)and Western Hemlock (Tsuga heterophylla). Canopy cover was relatively open and dominated by the conifers. Sites were an average of 69 m, and up to 300 m, from a stream or marsh; many sites were also close to openings such as marshes, fields, or houses. Since some sites were previously known owl locations, it could be that sites were biased towards man-made openings as owls in these areas would be more likely to be found by casual observers. Of six roost sites, four were in Western Redcedar. Roost heights were variable, but were on average 25 m above the ground. In the areas around roost sites, there was a small amount of shrub level cover, but what was there was composed primarily of Sword Fern (Polystichum munitum), Oregon-grape (Mahonia spp.), Salal (Gaultheria shallon), and Ocean Spray (Holodiscus discolor).

On southern Vancouver Island and the Gulf Islands, Hobbs (pers. comm. 2001), has found the owl in spring and summer months in a variety of habitats including those described as: mixed riparian woods, mature forest, 50 to 60 year old open Douglas-fir forest, dense young Douglas-fir forests and a mix of locations that are woodlands bordering marshes, ponds, other wet areas or fields. He has seen Western Screech-owls roosting in natural cavities in deciduous and Douglas-fir trees. Roosting birds were often seen high up in the crown of the tree. Cooper (pers. comm. 2002) feels that most screech-owls on Vancouver Island and the Lower Mainland occur in mixed riparian woods, woodlands adjacent to fields, and open coniferous forests. He has noted them in open Douglas-fir/Arbutus forests on James Island, just east of Sidney.

In the mid-1990s, Robertson et al. (2000) recorded Western Screech-owl roost sites in the Lower Mainland and in locations northward up the nearby mainland coast as part of larger inventory studies. The Lower Mainland encompasses an area from approximately North Vancouver south to White Rock and east to Chilliwack. Owls were often found in mixed deciduous-coniferous woods greater than 50 years old, but numerous birds were also found in a 25 to 30 year-old Douglas-fir plantation. Roosting birds, usually perched close against the tree trunk, were always in conifers, mostly Western Hemlock and Western Redcedar. The authors felt that dense conifer roosts were important for the survival of the species. Bowles (1917) also notes that during the daytime, this species is usually found in the ‘dark foliage of some young fir’.

It seems likely that O. k. kennicottii prefers deciduous or mixed forests in the south where the species is best known, but in a large part of its range it occurs primarily in coniferous forests (though it may well key in on deciduous trees for roosting and nesting). Three recent studies described below show that Western Screech-owls occur in good numbers in coniferous forests (Setterington 1998, Holroyd et al. 2000, Mico and Van Enter 2000). Hazelwood (pers. comm. 2001) says that screech-owls are generally reported from mature hemlock forests in Terrace, BC.

In a Clayoquot Sound in western Vancouver Island, Western Screech-owls were found in all three Coastal Western Hemlock (CWH) biogeoclimatic zones that they sampled (CWHvh1, CWHvm1, CWHvm2Footnote1) (Holroyd et al. 2000). In a Campbell River watershed study, in eastern Vancouver Island, owls were also recorded in second-growth Douglas-fir and Western Hemlock forests within the Coastal Western Hemlock zone (CWHxm1, CWHxm2, CWHvm1Footnote1), although precise habitat associations could not be made (Mico and Van Enter 2000). The five study areas were dominated by second growth Douglas-fir and Western Hemlock, with smaller amounts of Western Redcedar. At one site, Western Hemlock and Amabilis Fir (Abies amabilis) dominated.

A three-year study of owl abundance in the Nimpkish Valley of northern Vancouver Island indicated that Western Screech-owls were common in the coastal coniferous forests occurring there (Setterington 1998). Screech-owls were found in forest dominated by hemlock, Douglas-fir and Western Redcedar. The deciduous component of the parts of the forest where screech-owls were found was only about 3.7%, but this was still a statistically higher portion than in random plots where the deciduous component was about 1%. Based on forest cover maps, and not on on-the-ground vegetation surveys, the owls were found in forests with the following average characteristics: basal area of 44 m2/ha, stand age of 128 years, height of 25 m and 50% crown closure. The basal area was lower, forest age younger and crown closure less than in random plots.

Nests were not looked for in any of these three studies, thus it is not known what species of trees were being used as nest trees in these parts of the province. See Biology, Reproduction section for more information on nest trees.

Three other bird species at risk that occur in parts of BC in broadly similar habitat to the coastal subspecies of Western Screech-owl are the Queen Charlotte Goshawk (Accipiter gentilis laingi), Marbled Murrelet (Brachyramphus marmoratum) and the Spotted Owl (Strix occidentalis), though these three species often occur at significantly higher elevations than does the screech-owl.

Interior Subspecies – Otus kennicottii macfarlanei

In BC and Idaho, the interior subspecies O. k. macfarlanei  is usually described as inhabiting deciduous valley bottoms and low elevation riparian areas, and to a lesser degree wooded urban areas (Cannings et al. 1987, Hayward and Garton 1988, Campbell et al. 1990, Cannings 1997, Belthoff, pers. comm., 2001, S. Clow, pers. comm., 2001). Areas with Black Cottonwood (Populus trichocarpa) trees are often favoured (Cannings 1997, Belthoff, pers. comm., 2001).

At nine Western Screech-owl sites studied by Cannings (1997), breeding habitats were either of deciduous and mixed deciduous-coniferous forest types. Mature Black Cottonwoods were often present. Elevations of sites with owls were between 360 and 840 m, but were mostly below 600 m. Owl sites were either within riparian zones or up to 200 m away from the zone (all sites examined with or without owls were up to 300 m away). Birds were found roosting in coniferous and deciduous trees. In the Okanagan, screech-owls have been detected during the breeding period in slightly wetter habitats than those described above, that is, riparian, but with characteristics typical of poorly drained sites, such as standing water and vegetation typical of marsh habitats (Hobbs in prep.).

In the River of No Return Wilderness, Idaho, Hayward and Garton (1988) examined the habitat differences of five owl species. Western Screech-owls were much more likely to be found in places where deciduous tree cover was relatively high and were generally found in deciduous-dominated bottoms at the lowest elevations within the study areas (1175 m), but not in conifer forests of Douglas-fir or Lodgepole Pine (Pinus contorta) which were more common forest types. The same authors (Hayward and Garton 1984) examined the winter and spring roost sites of two Western Screech-owls in the same area. Roosting birds were found in riparian mixed deciduous and coniferous habitat within the area. They used only conifer roost sites in the winter, but after the leaves had appeared they roosted about half the time in deciduous trees but usually positioned themselves next to the bole of the roost tree. Roosts were also in areas of relatively greater tree density, suggesting to the authors that sites were chosen to provide both thermal and hiding cover.

Trends in habitat

Concerns over Western Screech-owl habitat focus on the regions of southern Vancouver Island and the Lower Mainland. In the former two regions, urban development continues, and inevitably leads to a decline in the amount of low elevation forested habitat (Fraser et al. 1999, Robertson et al. 2000).

In the interior of BC, the amount of wooded riparian habitat is decreasing significantly. Numerous sources have commented that development of riparian zones for housing, agriculture and forestry can and have affected the amount of available riparian woodlands in BC and Idaho (Cannings et al. 1987, del Hoyo 1996, Cannings et al. 1998, Belthoff pers. comm., 2001, S. Clow pers. comm., 2001). Recent analyses have indicated that about 87% of the water birch and 32% of the cottonwood habitats favoured by this species has disappeared from the Okanagan Valley over the past century (Dyer, pers. comm.).

Cannings et al. (1998) showed that much of the land in the south Okanagan that was riparian (or grassland) in 1940 had been converted to agricultural or urban habitats by 1987. They estimated that only 48% of the area that was riparian in 1940 remained in 1987, while the remainder was altered. Most of this land was converted to moist pasture or agricultural fields (Cannings et al. 1998). Areas of land under urban uses are also increasing.

Protection/ownership

In the Lower Mainland, southern Vancouver Island and the heart of the Okanagan Valley portions of the Western Screech-owl range, most of the land is privately owned. A small minority of the land where the bird has occurred is in protected local or regional parks, such as Pacific Spirit Regional Park near Vancouver, Campbell Valley Regional Park in Langley, and Woodhaven Nature Conservancy in Kelowna. Some habitat is protected in coastal provincial parks such as Goldstream and Helliwell and in Pacific Rim National Park. A new national park proposed for the Gulf Islands would protect a significant amount of habitat.

About 1,721 ha (11%) of potential Western Screech-owl habitat in the southern Okanagan is in conservation lands (MWLAP 2001). In the same study, the remainder of O. k. macfarlanei potential habitat was found to be 31% crown land, 32% Indian reserve, and 26% privately owned. These figures do not include newly created parks in the south Okanagan (e.g. White Lake Grasslands Provincial Park and South Okanagan Grasslands Provincial Park) that have significant amounts of suitable habitat.

There is no significant change expected in the ownership of habitats where the Western Screech-owl occurs.

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