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Posted by: atowhee | April 13, 2019

WHAT IS RARE? WHAT IS SIMPLY UNCOMMON? WHAT IS SIMPLY TO BE EXPECTED?

Take the White-throated Sparrow as a case study.
In one sense this is a rare species even when there are a lot of individuals around.  I  blogged about recent science on this bird…and the analysis that there are four sexes in a manner of description.  Click here to read summary of that research. 

Evidently, along with humans, it is a rare species that can claim multiple sexes.

In the eastern U.S. the white-throat is among the abundant species.  One autumn day I joined a bunch of New Yorkers birding Central Park.  They shrugged off a flock of these birds feeding along a path in The Ramble.  I lingered to look.  When later I mentioned that there was a White-crowned Sparrow in the flock, the other birders all went running back.  I was still naive about bird distribution in those days, not knowing that the White-crowns I heard daily in California all spring and early summer were a good find in New York.

Lately I’ve become puzzled about the bird’s wintering habits here on the Pacific Slope.  In years of Bay Area birding I saw one.  In Ashland every winter there would one to three in the same location, all winter.  You could hear the WTs sing there in spring before they departed.  For the past two winters I have had a wintering WT in my McMinnville garden.  Paul Sullivan sees them at his house.  His detailed records show at least one bird there every winter starting in 1997, usually present from November through April.  Today I saw three in my garden, two pale chests, one with a darker chest like its Golden-crowned cousin.  Is this a small flock heading back north?

I have to agree with “uncommon” which is the word used by Alan Contreras in two books: Northwest Birds in Winter and Handbook of Oregon Birds (with lead author Hendrik Herlyn). At what point does the species become expected but still uncommon which seems to be its status in the lowlands of western Oregon?  In Ashland the wintering birds were at 1800 feet elevation, here less than 200 feet.  Surely the birds that return annually to the same locations must be the same birds or at least their progeny?  We already know that many migratory species can be very loyal to specific locations.

It would be fascinating to compare the DNA of these Pacific wintering birds with their cousins that go east and then south….as well as the ones that always live east of Mississippi River.  There is a breeding population that breeds in northeastern British Columbia, due north of my house…but that’s also on the other side of the Canadian Rockies.  Surely these birds we see here are more than vagrants as they annually fly over the Rockies to get here.  None breed in the coastal lowlands.  Is this a fraction of the overall population that always migrates along the Pacific Slope?  Similar to the small population of Tree Swallows that always winter in the Sacramento River Valley rather than go further south?  Maybe some graduate student at OSU will do some analysis for us.

The first two pictures are Bird 1, the next two with more streaky chest is Bird 2.  Both are of the pale-chested variety.  The darker one got away when he was chased by a Golden-crown.  Click on any image to enlarge.  These guys showed up after the morning rain drizzled down to mist.  When real rain resumed, they vanished into cover.

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Responses

  1. Very Interesting. What about this: Seeing MALE rufous here for two weeks. NO FEMALES – come later?ALSO, where did they winter? SO. Cal or warmer?Thanks,m a


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