Thursday, March 11, 2010

Dark-eyed Juncos

 
After almost a week of fog and rain, I have not been able to do much field work.  Despite the rain, I have heard and seen more robins and juncos than I have previously this winter.  Perhaps these birds represent the vangard of the spring migration!

Check out this website for a detailed account of how to age and tell the sex of juncos and a few other birds: http://www.migrationresearch.org/mbo/id/scju.html#asyfw.  The site is intended for banders with birds in hand.  Some birders say that you can tell the sex of juncos by the amount of white in their tail feathers: this is a misconception--the amount of white is simply variable regardless of age or sex.  According to the website, banders can tell the age and sex of juncos by small differences in the wing covert shapes and colors.  I have always depended upon wing length and eye color.  Birds with wings under 72 mm are females, those 78 and more are male (with intermediate wings of unknown sex).  Under bright light, juncos with brown or grayish eyes are either hatching year or second year birds (depending on the season) while those with rich chestnut eyes are after-hatching birds.  The bird above has chestnut eyes.

Thanks to Larry Sirvio for giving me the lead to http://www.migrationresearch.org/mbo/id/scju.html#asyfw.

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