Subject: CALBIRD Bristle-thighed Curlew structure
From: Kimball Garrett
Date: Thu, 21 May 1998 10:10:52 -0700

 Calbird:

 Recent postings about structural differences between Numenius tahitiensis
 and N. phaeopus hudsonicus prompted me to look at our collection of both
 skins and skeletons of these taxa.

 Since it is difficult to examine "upper leg" (= tibiotarsus) length in
 study skins, I looked at skeletons of a couple of hudsonicus Whimbrels
 and our one tahitiensis. (The AOU skeleton inventory lists only 23
 tahitiensis skeletons in the world's collections, so forgive the small
 sample size).

                     tahitiensis                     hudsonicus
                     (one female)                    (mean of 2 females)

 tibiotarsus         87.7                            86.9

 tarsometatarsus     60.9                            63.7

 sternum (for
 overall size)       71.9                            74.3

 tib/tar ratio       1.44                             1.36

 tar/sternum
 ratio               0.85                             0.86

 These skeletal differences hardly inspire confidence in the usefulness of
 these aspects of structure in field identification, but do suggest that
 Bristle-thighed has a slightly shorter "lower leg" (tarsus) to "upper leg"
 (tibia) ratio.

 It may be of interest that the diameter (at the mid-point) of the
 tarsometatarsus in our one tahitiensis was 3.5 mm, but only 3.1 mm in
 our two hudsonicus, suggesting the notion of a thicker leg of Bristle-thighed
 might be accurate on not based solely on "fleshiness" of the tarsus.

 From an analysis of study skins (I excluded juvenile birds), I got
 the following:

                tahitiensis                     hudsonicus
 culmen  F      90.0 (n=7)                      92.6 (n=7)
                (83.3-97.5)                     (87.0-102.4)

 culmen M       79.7 (n=5)                      83.6 (n=5)
                (76.3-83.5)                     (78.2-88.0)

 wing  F        247.3 (n=6)                     250.6 (n=7)
                (233-258)                       (242-260)

 wing  M        237.0 (n=4)                     235.8 (n=4)
                (229-247)                       (230-246)

 tarsus  F      57.4 (n=6)                      58.6 (n=7)
                (55.4-59.5)                     (54.4-62.2)

 tarsus  M      54.5 (n=5)                      54.6 (n=5)
                (52.8-55.3)                     (51.0-60.0)

 Again, these data do not inspire confidence in the use of structure to
 separate these species.  Bristle-thighed does seem to be slightly
 shorter-billed on average, but tarsal differences are virtually nil.

 It is possible that perceived structural differences could be due to
 behavior and posture as much as true morphology.  Some who have suggested
 these differences are keen observers who indeed have looked carefully
 at lots of Whimbrels; I put less faith in perceived differences claimed
 by observers who probably never critically looked at variation in
 Whimbrels.

 As an aside, it is interesting that most of the CA, OR, and WA birds have
 apparently been silent. The whistled call of a Bristle-thighed Curlew is
 one of the most distinctive sounds in mid-Pacific atolls, and strikingly
 human-like in quality; needless to say, this call is utterly unlike
 anything given by a Whimbrel.

 Kimball L. Garrett

 **********************************************************
        Kimball L. Garrett
        Ornithology Collections Manager
        Natural History Museum of Los Angeles County
        900 Exposition Blvd., Los Angeles CA 90007 USA
        213/763-3368 phone; 213/746-2999 FAX
        kgarrett@nhm.org
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