Subject: Re: Sexing the SJCR Bristle-thighed Curlews.
Date: May 28 20:08:53 1998
From: Mike Patterson - mpatters at orednet.org
The following two items were posted last week to CALBIRD listserve. Dead
birds don't lie. The smaller birds were probably males and the Crescent City
bird was definitely a male:
Subject: Re: CALBIRD Bristle-thighed Curlew structure
From: Alvaro Jaramillo
Date: Thu, 21 May 1998 20:33:26 -0700
Birders,
Independently from Kimball I also measured some curlews today. I was
doing some work at the Museum of Vertebrate Zoology in Berkeley and took a
bit of time off to measure a few curlew bills. These are the data I came up
with:
number species sex culmen depth width
95095 BTCU F 105.3 9.98 7.45
100606 BTCU F 106.39 9.31 9.25
45128 BTCU F 90.15 8.24 7.04
45129 BTCU F 77.25 6.57 5.23
79436 BTCU M 90.22 9.82 7.49
12501 BTCU M 86.98 7.49 5.38
45127 BTCU M 86.8 8.06 5.92
12500 BTCU U 97.38 7.92 5.97
22321 WHIM F 97.87 7.11 6.58
22322 WHIM F 95.36 8.3 7.58
173820 WHIM F 86.69 7.43 7.12
87889 WHIM F 92.64 9.28 8.14
22323 WHIM M 87.95 7.27 6.28
22324 WHIM M 85.08 7 6.52
22326 WHIM M 83.51 6.72 6.38
22327 WHIM M 80.15 6.74 6.47
The number refers to the museum number. Note that the shortest billed
female was a juvenile and #45128 may have also been less than a year old
but I couldn't confirm this looking at the skin. Looking at Whimbrels it
was clear that juveniles had much shorter bills than adults, so keep that
in mind. If the short billed juvenile female is kept out of the analysis
the conclusions do not change, the means just shift about a bit.
These are the means (averages) for the measurements.
MEANS SEX culmen depth width
BTCU F 94.7725 8.525 7.2425
BTCU M 88 8.456666667 6.263333333
WHIM F 93.14 8.03 7.355
WHIM M 84.1725 6.9325 6.4125
In this case, the Bristle-thighed Curlew came out as the longer billed
species, for both sexes. Bill depth at the anterior end of the 'nostril'
averaged greater for the Bristle-thighed Curlew. For you statistics buffs,
the bill depth difference in males was the only statistically significant
(t-test at alpha = 0.05) comparison. Bill widths are roughly the same, but
note that in this sample of birds the Bristle-thighed Curlew is the thinner
billed bird.
morphometrically yours,
Alvaro
Alvaro Jaramillo "It was almost a pity, to see the sun
Half Moon Bay, shining constantly over so useless a country"
California Darwin, regarding the Atacama desert.
alvaro at sirius.com
Helm guide to the New World Blackbirds, Birding in Chile and more, at:
http://www.sirius.com/~alvaro
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 at nhm.org
**********************************************************
--
Mike Patterson, Astoria, OR _Birds and other Wildlife of the
mpatters at orednet.org Columbia River Estuary_
http://www.pacifier.com/~mpatters/bird/book_ad.html