The common grackle

Of the three species of grackle in North America, only one is found in Canada.  The boat-tailed grackle is native to Florida and the great-tailed variety is found in the westcentral and eastern states.  Common grackles are found only in the far northeast corner of BC but are present throughout all other provinces and throughout the states east of the Rockies.  They are a type of blackbird.

It is interesting to note there are at least eight subspecies of common grackle.  There is a particularly good visual guide to them on this website.  The one photographed above was shot in Central Alberta and represents the major subspecies throughout the continent.  Similar to the colours in hummingbird displays, the colour scheme of grackles is not actually colour based.  That is to say, the vibrant purple colour you see is not because of feather pigments but because of microscopic feather structure.  

You can see the colour-play based on lighting and angle of viewing.  The iridescent purple head seems black and dull from one viewpoint and brightly coloured from another.  This is all due to the fine feather structure that reflects light at particular wavelengths; the sheen or iridescent variation in colour changes with position.  Females are a bit smaller than males and lack the brilliant sheen.  Males have a "Keel-shaped" tail in flight.

Common grackles are one of the foremost feeders of corn crops.  Their voracious habits will take corn kernels at all stages of growth.  They do millions of dollars in damage every year to many varieties of crops.  A large flock of grackles can decimate a field in a short period of time.  Farmers use low-flying helicopters and bird call alarms to reduce damage. 

Thanks for reading.

Eric Svendsen     www.ericspix.com