Loggerhead shrike COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Loggerhead Shrikes prefer open country such as pastures, prairie grasslands, sagebrush, and agricultural fields. In all of these habitats, shrikes require scattered small trees, shrubs or hedgerows for foraging perches and nesting sites. Prescott and Collister (1993) found that shrikes breeding in relatively arid short-grass prairies in Alberta preferred areas of medium (15-35 cm) and tall (> 35 cm) grasses while foraging. Further east, shrikes appear to prefer areas with relatively short grass, apparently due to greater capture success in such habitats (Gawlik and Bildstein 1993).

Preferred nesting sites are small trees and shrubs, especially those with thorns or dense interiors (Porter et al. 1975). There is some indication that within seasons, nest site preferences shift from low (bushes, shrubs) to high (deciduous trees) substrates, apparently in response to changes in local climatic extremes. Bjorge and Prescott (1996) found that the density of breeding shrikes in southeastern Alberta was positively correlated with the density of native trees/shrubs, farmyards, shelterbelts and rights-of-way. Thus, vegetative diversity may be an important factor in habitat suitability.

Territory size has been shown to correlate negatively with the local abundance of trees and shrubs – that is, in sparsely wooded areas, territories are much larger than in well-wooded areas (Miller 1951, Yosef 1996). Mean territories of L. l. excubitorides in Alberta was 13.4 ha (range 6.5 to 23.5, n = 20; Collister 1994). In other areas of North America, territory size ranges from 4.6 (Missouri) to 8.9 ha (Idaho; Yosef 1996).

Trends

Most authors have concluded that suitable breeding, migration, and wintering habitat has declined and continues to decline (see discussions in Telfer 1992, Yosef 1996, Cade and Woods 1997). The primary loss of habitat occurs through conversion of native grasslands to agricultural crops. In Canada, habitat loss has also occurred as a result of grassland areas along the northern periphery of the range reverting to forest (Cadman 1986).

In Alberta, surveys of potential habitat have uncovered a number of shrikes breeding within the southern Aspen Parklands region (Kiliaan and Prescott 2002). In Saskatchewan, similar province-wide surveys suggest a contraction of the population and perhaps habitat in the southeast (A. Didiuk, in. litt.; Table 3). In Manitoba, the remaining population of shrikes continues to contract, despite the presence of apparently suitable breeding habitat within the former range (K. De Smet, pers. comm.).

Protection/ownership

The vast majority of suitable Loggerhead Shrike habitat in Canada is under private ownership. As a consequence, habitat protection must be carried out largely through voluntary land stewardship programs. Such programs include suggestions to fence off small areas of shrubs and shelterbelts, to protect trees (by placing fencing, or other barriers around them) from cattle, and to plant shrike-friendly trees such as thorny buffalo-berry (Shepherdia argentea). Despite the availability of literature and expertise on these subjects, there are no data available on the extent to which they have been adopted by private landowners.

There are currently efforts underway in Saskatchewan (Didiuk, pers. comm.) to first identify and then to protect known areas of suitable/preferred shrike habitat. Similar proposals have been made for Alberta (e.g., Prescott and Bjorge 1999) and Manitoba (De Smet, pers. comm.).

In Alberta, large numbers (ca. 1400) of buffalo-berry shrubs have been planted along the Canadian Pacific railway line in the southeast. There are also various land ownership proposals underway in Alberta that strive to protect areas of high shrike density (see Prescott and Bjorge 1999). Operation Grassland Community provides some extension work to landowners concerning Loggerhead Shrikes.

Page details

Date modified: