[obol] Re: Bell's Sparrow -- A Potential Addition to the Oregon List???
- From: David Irons <llsdirons@xxxxxxx>
- To: Pete Fahey <peterfahey@xxxxxxxxxxx>, OBOL Oregon Birders Online <obol@xxxxxxxxxxxxx>
- Date: Sun, 4 Aug 2013 05:51:06 +0000
Greetings All,
Since my post earlier today, I received a couple of responses that may be of
interest to the entire group. I will address both separately in a single
message that goes back out the group.
First, I got this great question from a birder in Washington. In the interest
of his privacy, I won't use his name.
I am a bit confused. For the purpose of this question, Sibley lists belli
(Bell’s) and nevadensis/canescens (Interior) in his subspecies list . Has the
AOU changed that, and now lists canescens as a subspecies of belli? Thanks
Let's start with David Sibley, who is not a taxonomist. He's a field guide
author, thus his mission is to organize his work in a way that helps simplify
the subject matter for us (the users). To his credit, Sibley has generally
resisted the temptation to name subspecies in his guides, as this has inspired
many birders to slap names on subspecies that really can't be positively
identified in the field. The subspecies formerly known as Artemisiospiza belli
belli ("Bell's Sparrow") is one of the few instances where he uses a colloquial
subspecific name his guides. Instead, Sibley opts to group birds geographically
or biogeographically. Throughout his field guide he liberally uses Eastern,
Western, Pacific, Atlantic, Taiga (the boreal belt), Prairie, Coastal,
Interior, and Tundra when labeling his illustrations of the forms that occupy
various geographical regions.
Speaking to the specific question above, let's first consider that until
yesterday–or whenever the 54th Supplement to the AOU Checklist was released–A.
b. belli, A. b. nevadensis, and A. b. canescens enjoyed equal footing. All were
subspecies of Sage Sparrow. True to form, Sibley grouped (a group of one) the
coastal form (A. b. belli) under one heading and grouped the two interior forms
(A. b. nevadenis and A. b. canescens) under another heading. Note, that this is
not done in his field guide, as neither nevadensis or canescens are mentioned
in his text. I'm not sure where Sibley published the information referenced
above. As I edited images today I noted that canescens is in some respects more
like nevadensis than belli in appearance, which makes sense because interior
desert/prairie/Great Basin subspecies tend to be paler overall than there
coastal counterparts.
Assignments and reassignments are made by the AOU Checklist Committee on the
basis of phylogeny–the lineages and chronological evolutionary relationships
between species and groups of species–and taxonomy–the classification of
organisms based on natural relationships. While it seems intuitive that
organisms occupying the same biogeographical region and sharing similarities in
appearance would be closely related, that's not always the case. Today's
taxonomists are looking at phylogentic relationships on a molecular level, thus
similarity in appearance and in particular geographical proximity often have
little to do with the ultimate placement of a species or subspecies. Clearly,
the study of various subspecies/species in the "Sage Sparrow" complex has
revealed information that suggests a closer relationship between belli and
canescens, with nevadenis being the outlier. That said, there is already
rumbling that canescens may eventually become a full species as well.
Taxonomies are highly plastic and ever changing. Birds that we consider closely
related today, may well be moved tomorrow to a place in the order that isn't
immediately understandable. Think of last year's migration of falcons away from
raptors and next to the parrots.
################################################
The second response came from Wayne Hoffman, who shared his photos of a Sage
Sparrow that showed up at Newport last year. Wayne took a second look at it and
concluded that it was a Sagebrush Sparrow. Unfortunately for Wayne, who I know
would dearly love to be the one to add this species to the Oregon list, it is
indeed a Sagebrush Sparrow. His excellent photos leave no doubt. Wayne went on
to suggest:
Given Bell’s Sparrow’s range and less-migratory habits, I would expect Oregon’s
first to be in mid-late summer in Jackson or Klamath county.
When I suggested the potential that some of the spring overshoots in w. OR
could be Bell's Sparrow rather than Sagebrush Sparrow, I knew that this would
be an unlikely scenario, even though the northern end of Bell's Sparrow's
breeding range may be within a 150 miles or so of the Oregon border. Generally
speaking, spring overshoots, or extralimital strays, originate from the most
migratory population and not from the most proximal population, especially if
that population is relatively sedentary. Across much of their range, Bell's
Sparrows are all but non-migratory, so there is no migration to overshoot from.
I fully agree with Wayne's comment above, wherein he suggests that a late
summer stray (post breeding dispersal) is probably a far more plausible
scenario for producing Oregon's first Bell's Sparrow. However, to my knowledge,
there are no summer records of juvenile Sage Sparrows from western or
southwestern Oregon. If you intend to be a hero and find the first, I would
encourage you to study photos of juvenile Sage Sparrows and learn how to
separate them from juvenile Dark-eyed Juncos and the more expected Vesper
Sparrow. One key difference is that Bell's Sparrow does not have white outer
tail feathers, but otherwise a juvenile Bell's Sparrow could easily be passed
off as one of these two. Just this week a juvenile Bell's Sparrow (it was still
a Sage Sparrow when it was found) turned up in Humboldt County, California,
roughly 100 miles from the Oregon border. I've seen the photos and there seems
to be little doubt that it is a Bell's Sparrow.
I hope that I've made sense in the lengthy post above.
Dave IronsPortland, OR
Other related posts:
