Loggerhead shrike COSEWIC assessment and status report: chapter 11

Summary of Status Report

Prairie Loggerhead Shrikes have undergone significant range retraction and population declines in recent decades. Since the original designation of Threatened in 1986 (Cadman 1986), populations in Manitoba have continued to decline sharply, while those in Saskatchewan have shown less drastic declines, and in Alberta, the species appears more or less stable. One problem in assessing current population trends is that the abundance of shrikes in Canada is now so low that BBS data have low statistical power. Ongoing surveys in Alberta and Saskatchewan should provide a much better picture of the status and population trends in the core of the species’ Canadian range. Recent (1993-current) data from the known wintering areas (southcentral USA) of the Canadian population also suggest an ongoing decline in numbers.

The reasons for the declines in range and abundance are still unclear. Loss and/or degradation of grassland habitats, pesticide accumulation, predation at nest sites, and collisions with vehicles have all been cited as potential contributors. Although recent attempts have been made to improve breeding habitat (e.g., by planting shrubs in grassland areas, fencing potential nesting trees), there has not been sufficient time to assess the effects of such treatments.

In addition to the decline in population size in Manitoba, reproductive success there has declined since 1993, thus contributing to the overall population crash. Although there are currently no long-term reproductive data for Alberta and Saskatchewan shrike populations, such data are currently being collected in Saskatchewan.

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