From south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Tue Aug 19 11:47:20 2003 Received: from www.plaidworks.com (localhost [127.0.0.1]) by plaidworks.com (8.12.9/8.12.9) with ESMTP id h7JIhKkU020828 for <[[email protected]]>; Tue, 19 Aug 2003 11:43:20 -0700 (PDT) Received: from rtjones.nas.nasa.gov (rtjones.nas.nasa.gov [129.99.19.30]) by plaidworks.com (8.12.9/8.12.9) with ESMTP id h7JIfOVK020768 for <[[email protected]]>; Tue, 19 Aug 2003 11:41:28 -0700 (PDT) Received: (from mrogers@localhost) by rtjones.nas.nasa.gov (SGI-8.9.3p2/8.9.3/NAS 8.9.3-5n) id LAA65300 for [[email protected]]; Tue, 19 Aug 2003 11:41:23 -0700 (PDT) Date: Tue, 19 Aug 2003 11:41:23 -0700 (PDT) From: "Dr. Michael M. Rogers" <[[email protected]]> Message-Id: <[[email protected]]> To: [[email protected]] Subject: [SBB] Ruff vs Reeve X-BeenThere: [[email protected]] X-Mailman-Version: 2.1.2+ Precedence: list List-Id: South Bay Birding List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Errors-To: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] All, There has been some confusion about the sex of our Alviso Ruff, so I thought I'd elaborate on this issue for those who do not have access to the references cited below. If you find such details boring you may want to hit the delete key. There is no overlap in size between male and female Ruffs and it is usually possible to sex this species on this basis alone. Conventional wisdom has it that Ruffs are similar to Greater Yellowlegs in size, whereas female Ruffs (Reeves) are similar to Lesser Yellowlegs. The Sibley guide does not give separate sizes for male and female Ruffs, but only indicates that males are "20% larger". The NGS guide (3rd edition) lists the length (bill tip to tail tip) of a male Ruff as 12" (31 cm) and of female as 10" (25cm). The two yellowlegs are listed as 14" (36cm) and 10.5" (27cm), so perhaps male Ruffs aren't really as big as a Greater Yellowlegs? On the other hand, a lot of that 14" for the Greater Yellowlegs comes from its longer bill length, so how do the two compare in bulk? Fairly small differences in length can make fairly big differences in weight because the weight of a bird is roughly proportional to its volume, which increases roughly like the cube of its length (when comparing birds of similar proportions). Sibley lists the weights of Greater and Lesser Yellowlegs as 160 grams and 80 grams, respectively, - a full factor of two difference in weight despite only a 33% difference in length and 17% difference in wing span. The Ruff is listed at 150 grams, but separate numbers for the two sexes are not included. Those with an interest in shorebirds would do well to own "Shorebirds of the Pacific Northwest" by Dennis Paulson. This book is filled with outstanstanding photographs and information. One of the many useful features is Appendix 3 "Shorebird Weights and Measurements". From this we can find the following: Weight tarsus bill grams mm mm male Ruff 180 50 35 Greater Yellowlegs 170 63 56 female Ruff 109 43 31 Short-billed Dowitcher 105 37 60 Long-billed Dowitcher 105 39 67 Lesser Yellowlegs 76 51 36 female Wilson's Phalarope 68 34 34 male Wilson's Phalarope 50 32 31 Thus nearly one inch of the difference between the bill tip to tail tip lengths of a Greater Yellowlegs and a male Ruff is indeed caused by the bill length. Presumably the other inch of difference is related to the longer neck of the yellowlegs since on average the above numbers indicate that a male Ruff is actually heavier than a Greater Yellowlegs! We can also see that a Reeve is on average quite a bit heavier than a Lesser Yellowlegs - in fact, even an average Reeve will be slightly heavier than an average dowitcher! Back when we had multiple Ruffs present at the CCFS waterbird pond we could get a good feel for this size difference. Reeves were typically similar in size to the dowitchers, often being difficult to find when in the middle of large flocks of them. Male Ruffs towered above the dowitchers and were easily picked out from among them. When the Alviso bird was originally found this fall it was likened to a dowitcher in length, suggesting a female to me and my subsequent observation of the bird confirmed this impression. Of course, not all all birds are average and some large female Ruffs may be harder to distinguish from small males. The "Guide to the Identification and Ageing of Holarctic Waders" contains a sampling of measurements (wing, bill, and tarsus) separated by age and sex for many shorebird species. For Ruff we find that there is some overlap in bill length (97 males:31-39mm; 71 females:26-33mm) and tarsus length (104 males:45-44mm; 71 females:37-45mm) but no overlap in wing length (101 males:176-196; 69 females:148-167mm). The text states "at all seasons completely separated by wing length: male greater than or equal to 175mm, female less than or equal to 170mm". Of course wing length is hard to judge, but the average differences adult male 188.7mm juvenile male 186.0mm adult female 155.5mm juvenile female 156.3mm do confirm that there should typically be a 20% size difference even though the largest female may be only 3% smaller than the smallest male. Another hint for ageing fall adults is also listed in the text: "male unmistakeable with ruff and head tufts distinctive to late August". Our bird, found in early August, is unlikely to be an adult male based on this plumage feature alone. Another great shorebird book is Hayman, Marchant, and Prater's "Shorebirds An Identification Guide to the Waders of the World". This book also lists ranges of measurements (lengths of bill tip to tail tip, wing, bill, tarsus, and tail) for both Ruffs and Reeves. Their ranges in overall length (males:260-320mm (11.5"); females:200-250mm (8.75")) suggest an even greater average difference of about 30%, with the closest males and females being about 4% apart - thus their statement "with experience it is usually possible to sex even a lone Ruff in the field". (Note the corresponding measurements for Greater and Lesser Yellowlegs are given as 290-330mm (12.25") and 230-250mm (9.5"), respectively.) Bottom line, if your Ruff is similar in size to a dowitcher its probably a Reeve. Mike Rogers _______________________________________________ Do not post admin requests to the list. They will be ignored. south-bay-birds mailing list ([[email protected]]) Help/Unsubscribe/Update your Subscription: http://www.plaidworks.com/mailman/options/south-bay-birds/south-bay-birds-archive%40plaidworks.com This email sent to [[email protected]]