Loggerhead shrike COSEWIC assessment and status report: chapter 4

Distribution

Global range

Loggerhead Shrikes have a wide breeding range in North America (Figure 1). The Prairie subspecies, L. l. exubitorides breeds from central and southeastern Alberta, central and southern Saskatchewan, and southwestern Manitoba, south through Montana, Wyoming, eastern Colorado, eastern New Mexico, Texas and into Sonora and northern Durango in Mexico (Figure 2; AOU 1957, Phillips 1986, Burnside 1987). Exact western and eastern range limits are not clearly defined, as populations apparently intergrade with L. l. gambeli and L. l. nevadensis in the Rocky Mountain region, and with L. l. migrans in the Great Plains and eastern Canadian prairies (central and eastern Manitoba). Due to apparent mixing of subspecies, the wintering distribution is poorly understood. In the northern portions of the range (including Canada), the species is migratory, while southern birds (Texas, Oklahoma) show some annual residency. Adults and juveniles banded in Alberta and Saskatchewan have been found in southern Oklahoma and central Texas in winter (Burnside 1987).

Figure 1.  Global range of the Loggerhead Shrike in North America (modified from Yosef 1996).

Figure 1.  Global range of the Loggerhead Shrike in North America(modified from Yosef 1996).

Figure 2. Approximate range of L. l. excubitorides in North America (modified from Burnside 1987).

Figure 2.  Approximate range of L. l. excubitoridesin North America(modified from Burnside 1987).

Canadian range

In Canada, Prairie Loggerhead Shrikes occur as breeders only in Alberta, Saskatchewan and Manitoba (Figure 3). Winter records are exceptionally rare in Canada, as the winter range is the southern US and northern Mexico (see Figure 1).

Figure 3.  Range of L. l. excubitorides within Canada.

Figure 3.  Rangeof L. l. excubitorides within Canada.

In Alberta, the species has been found historically throughout the Aspen Parkland and Prairie regions (Salt and Wilk 1958). In recent decades, the range has contracted southward and there are fewer summer records in the Aspen Parklands. The core of the range in Alberta now appears to be the northern half of the province’s grasslands eastward from Hanna and Brooks (R. Bjorge, in litt. 2004). However, recent surveying efforts in east-central Alberta have produced a number of breeding records in the southern Aspen Parkland region east of Stettler (Kiliaan and Prescott 2002).

The breeding range in Saskatchewan has also contracted southward. The species is still widely distributed in Parkland and Grassland areas, but it no longer breeds in most areas of central Saskatchewan (Meadow Lake, Nipawin, Somme areas; Smith 1996). Within the current distribution in southern Saskatchewan, populations are patchily distributed (A. Didiuk, pers. comm.).

In Manitoba, L. l. excubitorides overlaps and intergrades with L. l. migrans in the central portion of the province. L. L. excubitorides formerly nested north to the Interlake district, but is now largely confined to southwestern Manitoba.

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