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SWALLOW TALES (TAILS)—A LESSON IN JIZZ

By Nic.Korte

This butterfly is called a pale swallowtail—a common species in Western Colorado. (Yes, many birders can identify a few butterflies—more on that in a later blog.)   I have seen these in the mountains and in my yard this year.  But, this essay is a tale about swallows and their tails.

   Did you realize there are seven species of swallows that are relatively easy to see in Western Colorado?  With a little planning, I could probably find them all in a long morning.  Cliff swallows nest under bridges and nearby cliffs and are common near the Colorado National Monument.  Barn swallows, perhaps the most widespread, can be found over most fields and lowland ponds.  Rough-winged swallows can be found along streams too—such as Plateau Creek.  Bank swallows and purple martins are a little more local, but I know some nesting locations.  We’ll get to the other two—tree swallows and violet-green swallows, below. 
    In contrast to swallows, if someone asked me to show them all the thrushes that live here, or all the owls, even though we could be certain of being in the right habitat—those birds might not show themselves.   Swallows make it easy because they feed 100% on flying insects which means they are out over open areas making them easy to spot—but not always so easy to identify. 
Two species very easy-to-see in mountain meadows—but also, at times, anywhere in the valleys, are violet-green swallows and tree swallows.  Both have green iridescence and the typical swallow wings that seem longish and pointed. 

   When adult males are perched, their differences are easy to note.  See the dark face of the tree swallow on the left and the white face of the violet-green on the right?  The violet-green swallow is a little smaller and often it is possible to see its white rump patch when in flight.  Unfortunately, they don’t always perch close by and in good light.  Even worse, the females are drab and juvenile violet-green swallows may have a dark face.  Now how can you tell them apart?  Especially in flight?  Why by their jizz, of course!
   According to Wikipedia, “there is a theory that [jizz] comes from the World War II acronym GISS for ‘General Impression of Size and Shape (of an aircraft).’  More likely, jizz is a corruption of gestalt, a German word that roughly means form or shape, or more obviously of the word gist which has the same meaning.”  But you get the idea.  The clue is in the photos.  Look at the tails.  Notice that the tree swallow has a tail as long as its wings.  Not so for the violet-green swallow which has a short tail--and almost a bullet-like appearance in flight. 
   For many years, all birding field guides emphasized field “marks” such as the white face or the rump patch of the violet-green.  That only works for a perched, fresh-plumaged adult male so the newer generation of field guides puts more emphasis on a bird’s structure or in birding lingo—jizz.  Now you know how an experienced birder can make a quick glance at greenish, dark swallows flying into the sun and confidently identify them.  It isn’t so difficult after all.  This post provided by Nic Korte, Grand Valley Audubon Society.  Send questions/comments to nkorte1@hotmail.com]To learn more and to participate in the activities of Grand Valley Audubon, please see our website at audubongv.org and “like” us on Facebook!]

 

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