Dark Sharp shinned Hawk Accipiter Striatus from California Is Melanistic

2009·1.2 MB·English

by  William S Clark

WilliamS. Clarketal. 254 Bull. B.O.C. 2009 J29(4)
Dark Sharp-shinned Hawk Accipiter striatus from
California is melanistic
&
by William S. Clark, Michael A. Patten John C. Wilson
Received 7February2009
Patten &Wilson (1996) reported a darkSharp-shinnedHawk
Accipiter striatus that was represented as a colour morph previ-
ously unknown for this species (Bildstein & Meyer 2000). The
claim was based on two photographs of a perched juvenile
female, one included as their Fig. 1, taken in 1994 by JCW in
southern California. Clark & Wheeler (1997) disagreed that this
hawkwas a darkmorphand opined thatitwas a darkindividual
of the dark Pacific Northwest subspecies A. s. perobscurus. That
possibility was denied by Dickerman (2004), who, after examin- Figure 1. Melanistic Sharp-
ing the original slides, could not determiniei'.ifiitli/s -a-moirph, a shinned Hawk Accipiter
ph-,ase,or, morelTiikel1y, s.impl1ystai.ned1,1butthe bird definitelycan- s^f9n9a4h/(sJ,ohsnouCtheWrilnsCoanl)ifornia,
notbe identified as perobscurus.'
MAP andWSC metrecentlyand studied the originalphotographs, as Clark &Wheeler
(1997) had only seen thepublished photo. We now agree that the hawkwas notA. s. perob-
scurus, nor was it a 'dark morph', a term we feel applies best to a plumage persistent in a
population rather thanjust aberrancy. We instead feel that thebirdbestfits the description
'melanistic'. Similar aberrant plumages have been described as melanistic for many bird
species, for example: Pileated Woodpecker Dryocopus pileatus (Short 1965), Tree Swallow
Tachycineta bicolor (Campbell &Siddle2006), Blackcap Sylviaatricapilla (Bertholdetal. 1996),
and Cory's Shearwater Calonectris diomedea (Bried et al. 2005). It has also been used to
describe aberrant plumages in raptors, for example: Northern Harrier Circus hudsonius
(Howelletal. 1992, Olson & Osborn2000), OspreyPandion haliaetus (Clark 1998) and Black-
breasted Buzzard (Eagle) Geranoaetus melanoleucus (Clark & Schmitt 2006).
There remains confusion aboutuse ofterms. For example, inhis authoritativebook on
the subject, Majerus (1998) defined melanism 'to mean simply: the occurrence in a species
of dark orblack forms', and Butcher & Rohwer (1989) noted of color dimorphism or poly-
morphismthat'Manyoftheseinvolvemelanism'. Bycontrast,Thomsett(2007)assertedthat
'The terms melanistic and dark morph should not be interchangeable if the aetiology of
these conditions is not clear'. We contend that most scientific literature, bird guides, and
handbooksusetheterm'darkmorph'forregularlyoccurringdarkplumagesofbirds,acon-
dition unknown in the A. s. velox subspecies of Sharp-shinned Hawk, although South
Americantaxa in theSharp-shinned Hawk species complex (e.g.A. [s.] ventralis) dopossess
a true dark morph. With the terminology clarified, we therefore conclude that this Sharp-
shinned Hawkwas a melanistic individual, the first tobe recorded in NorthAmerica.
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Addresses: William S. Clark, P.O. Box 531467, Harlingen, Texas 78550, USA. Michael A. Patten, Oklahoma
BiologicalSurveyandDept.ofZoology,UniversityofOklahoma,Norman,Oklahoma73019,USA.John
C. Wilson, 1425AltaVistaDrive,Bakersfield,California93305,USA.
©BritishOrnithologists'Club2009