Subject: Re: status of R-t Hawk morphs/subspecies in Pac. NW
Date: Mar 18 01:08:06 1998
From: Jack Bowling - jbowling at direct.ca


** Reply to note from Charles Swift

> Recently somebody posted that they had seen Krider's Red-tailed
> Hawk somewhere in the area, however, my Peterson Hawks (Clark & Wheeler)
> indicates that they are generally found in the Great Plains during the
> summer and in the central south in the winter. So what is the status
> of this sub-species in the PAC NW? I would not have thought they would
> make it here.

> The Peterson book also mentions that Harlan's subspecies winters primarily
> in the central south (Arkansas, Missippi, Texas, Oklahoma, Missouri) and is
> widespread but rare elsewhere. Around Moscow both the rufous and dark morph
> of the Western Red-tailed Hawk are regular (but less common than the light
> morph).

> I assume that all of these dark morphs require good looks and careful
> identification when considering Harlan's as a possibility. Most of the Harlan's
> reports seem to be coming from the western side of Washington (this seems
> reasonable as this subspecies nests in Alaska & I assume are
> migrating down the coast). So I'm wondering if there's any discernible
> pattern to the distribution of the Harlan's subspecies in the PAC NW and
> also for the dark morphs of the Western Red-tailed Hawk (particularly west of the
> Cascades).

These are all good questions, Charles. I have written to others interested in this over the
years. The Red-tailed Hawk is what is called a "plastic" species i.e. one with many
recognizable phenotypes. The western subspecies _Buteo jamaicensis calurus_ (calurus
means "beautiful tail") has a high proportion of dark morph birds, I would estimate as
high as 40% in the B.C. population. However, other subspecies such as the coastal B.C.
and Alaskan _B. j. alascensis_ ,and the eastern continental _B. j. borealis_, have a very
low proportion of dark birds - in fact, dark morphs may be unknown in _alascensis_
(Alaskan Tweets please correct me here if needed).

The Harlan's Hawk _B. j. harlani_ is pretty well the darkest form, characterized by
a tail mottled to varying degrees with blackish and grayish longitudinal streaking. This
tail pattern is really the only reliable method of differentiating between dark morph
_calurus_ (reddish tail) and _harlani_ (streaked tail). There are other consistent
differences such as amount of barring on the primaries but this requires an exceptionally
good look with the bird in hand or in flight overhead. Harlan's can be found just about
anywhere in the PNW in the winter, but tend to favor the same open country with good
rodent populations that other Red-tails do.

Re. the reports of Krider's Red-tails _B. j. krideri_ in the PNW: I am not convinced that
they are indeed the _krideri_ form. If we accept _harlani_ as being the phenotypic
expression of a "dark" genotype, then what would happen if the normal _harlani_ gene
pattern gets flipped such that instead of the dark plumage being expressed, a light
-plumaged one results instead? I think that most if not all of these reports of _krideri_
in the PNW are indeed _harlani_ variants. The proportion of this form in the whole of the
_harlani_ pool must be necessarily low if it is a recessive trait. Some would argue that
_krideri_ may be just that: the light recessive half of _harlani_ that managed to produce
a big enough gene pool for the recessive to become dominant. In effect, any "light"
Harlan's would then by defintion be a Krider's. I am not convinced that a chance recessive
mutation belongs in the greater gene pool, however, since the individual variation within
the _krideri_ pool would likely be quite low compared to a chance individual.

Naturally, there are potentially albinistic or leucistic individuals of *all* the various
Red-tail Hawk forms in this part of the world. However, pure albinos usually stand out
like a sore thumb with their pale bare parts and pink eyes, and leucistic individuals by
definition have only parts of the plumage light-colored.

Something that has never been determined to my satisfaction is the amount of gene flow
across the various forms. Do _borealis_ ever mate with _calurus; _harlani with either
_calurus_ or _borealis_? This is particularly a propos given the current rage to split
everything possible into various species. Comments appreciated.

- Jack



------------------
Jack Bowling
Prince George, BC
jbowling at direct.ca