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Juv. Gray Hawk vs. Juv. Gray-lined Hawk

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  • Joseph Morlan
    In the most recent 53rd Supplement the AOU split the Gray Hawk (Buteo nitidus) into two species, northern Gray Hawk (Buteo plagiatus) and southern Gray-lined
    Message 1 of 1 , Nov 27, 2012
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      In the most recent 53rd Supplement the AOU split the Gray Hawk (Buteo
      nitidus) into two species, northern Gray Hawk (Buteo plagiatus) and
      southern Gray-lined Hawk (Buteo nitidus). In this decision they cited a
      publication by Milsap et al. (2011).

      According to BNA these two species differ in juvenal plumage as follows.

      GRAY HAWK - "Juvenile has dark crown, dorsal webs of outer primaries white
      due to light barring, 5–9 dark bars on tail, barring on thighs, markings on
      underparts sparser and smaller (more streaklike)"

      GRAY-LINED HAWK - "Juvenile has light crown with few dark streaks, dorsal
      webs of outer primaries orangish-buff, 0–6 dark bars on tail, streaked or
      immaculate thighs, and heavier spotlike markings on underparts."

      Currently a bird identified as a juvenile GRAY HAWK is being seen in Santa
      Barbara, California and is widely regarded as the first fully documented
      bird for the state, although whether the Gray-lined Hawk is fully
      eliminated as been raised.

      Here is a selection of photos of the Santa Barbara bird:

      https://picasaweb.google.com/112315979323323290821/GRAYHAWK

      http://www.flickr.com/photos/dd_thornton/sets/72157632111022150/

      http://www.westernfieldornithologists.org/gallery/displayimage.php?pid=574

      http://www.flickr.com/photos/36688066@N04/8219416246/

      http://youtu.be/--tA2al1zvU (video)

      Based on the photos and the BNA descriptions, the bird seems to best fit
      Gray Hawk in that it appears to have a dark crown, at least 9 dark tail
      bars, and some barring on thighs.

      The paper by Milsap et. al contains a useful color plate (see PDF below)
      showing some additional differences between these two species. Juv.
      Gray-lined has large dark blotches on the underparts, more less white on
      the uppertail coverts and has a pale window on the upperside of the
      primaries while Gray lacks large dark ventral blotches, has more white on
      the uppertail coverts and lacks pale windows on the primaries.

      Reference:

      The Auk 129(3):573-588, 2012
      (http://www.aou.org/auk/content/129/3/0573-0588.pdf)

      Bibles, Brent D., Richard L. Glinski and R. Roy Johnson. 2002. Gray Hawk
      (Asturina nitida), The Birds of North America Online (A. Poole, Ed.).
      Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North
      America Online: http://bna.birds.cornell.edu/bna/species/652

      doi:10.2173/bna.652

      Millsap, B. A., S. H. Seipke, and W. S. Clark. 2011. The Gray
      Hawk (Buteo nitidus) is two species. Condor 113:326–339.
      (http://globalraptors.org/grin/researchers/uploads/146/millsap_et_al._gray_hawk.pdf)




      --
      Joseph Morlan, Pacifica, CA
      "It turns out we're very good at not seeing things" - Jack Hitt
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