Saturday, December 13, 2014

Northern Shrike

John Holden and I took this photo just west of Northfield on 10 December 2014. Gray, foggy days are not really conducive for digital photography. Furthermore, birds perched on telephone wires do not usually produce very aesthetic compositions. But freezing fog combined with the wires to make this photograph of a Northern Shrike slightly more interesting than I predicted.

Elsewhere I have blogged about identifying Northern and Loggerhead shrikes. The thin black mask that does not traverse the fore-crown indicates this bird is a Northern Shrike. The bill is not as stubby as a Loggerhead's. Especially in the winter, Northern Shrikes consume many small birds and mammals, which they impale on barbed-wire, thorns, and in tree branch forks. Due to their razor-sharp bills, Northern Shrikes are one bird that I do not like to band.

Northern Shrikes are found across the Arctic areas of the Northern Hemisphere. Birds in Europe and Asia, where they are named Great Grey Shrikes, are found further south than are North American ones. Our Northern Shrikes typically move erratically in the winter only to the Central United States.

Northern Shrike systematics are murky. Within North America, ornithologists question if eastern and western races exist. Northern and Great Grey shrikes used to be treated as separate species. In any given sample of Old and New World birds, you can identify about 75% of the birds as to their origin. Does this fact indicate we are dealing with different species or just two quite variable subspecies?  Old World populations may actually represent as many as three additional species. One factor contributing to this confusion is that these shrikes are widely spread geographically, especially in their breeding range, making the collecting of meaningful samples very difficult (Cade and Atkinson 2002).

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