Shai and Joe, Great job by both of you. I learned a great deal from this discussion! If only I possessed the visual acuity to actually discern these details...
Bob Grover d +1 (631) 761-7369 | c +1 (516) 318-8536 -----Original Message----- From: bounce-122638150-3714...@list.cornell.edu <bounce-122638150-3714...@list.cornell.edu> On Behalf Of Joseph DiCostanzo Sent: Thursday, June 14, 2018 11:35 AM To: Shaibal Mitra <shaibal.mi...@csi.cuny.edu> Cc: NYSBIRDS (NYSBIRDS-L@cornell.edu) <NYSBIRDS-L@cornell.edu> Subject: Re: [nysbirds-l] Dark billed, dark legged Common Terns on Long Island Shai, I certainly did not intend to “categorically dismiss” any line of evidence. And I certainly did not mean to say longipennis is an impossibility (see my last post to Bob). I think we completely agree that there is a tendency to not think “quantitatively” - no where enough consideration is given to variability in common species. So when an individual does not fit the “field guide” picture of the common species there is often a tendency to immediately go for something rare instead of giving enough consideration to variation in the more likely occurring species. Of course rarities do occur! Birding wouldn’t be nearly as much fun as it is without them. The operative word, however, is “rare”. As the saying goes in medial diagnostics, “If you hear hoofbeats in the distance, think horse, not zebra.” (Unless, of course, you are in Africa. :) ) Joe Sent from my iPad > On Jun 14, 2018, at 10:49 AM, Shaibal Mitra <shaibal.mi...@csi.cuny.edu> > wrote: > > As I mentioned in my earlier note to the list on this subject (8 Jun 18, > copied at the very end of the present note), the jury is certainly still out > on the status of longipennis Common Terns on the east coast. Joe's highly > informed contributions are a very welcome addition to the process and > underscore several areas to focus on in resolving the matter. First, it is > clearly true that to claim an extralimital longipennis, the evidence must be > very strong and include multiple characters beyond dark bills and dark legs. > I have a lot to contribute on this front, because I have made a point of > studying non-breeding terns for more than 20 years, during which time I have > collected detailed data on large samples of carefully scored first-summers > and "second-summer types" (a category which, as Joe notes, consists of an odd > amalgam of a subset of some but not all two year-olds, older adults short of > full breeding condition, and very old, senescent adults)--not only of Common > Terns, but also of Arctic, Roseate, Least, Black, and others. > > For now I just want to make two very simple points in response to the queries > Joe raises toward the end of his note. > > First, I'd like to address Joe's skepticism about judging wing length > visually. I once wrote a long, detailed note to the ID Frontiers list > defending the critical, visual assessment of shape (i.e., the relative sizes > of morphological structures; that piece concerned warblers, or maybe willets, > or maybe I did it separately for both?). I might be able to dig it/them up, > but for now I remember demonstrating that large samples of in-hand > measurements counter-intuitively often obscure real differences between > similar species, males and females, etc. The reason is that handbooks > over-emphasize extreme data, neglecting quantitative measures of variance and > covariance, and because most observers are unprepared or unwilling to think > quantitatively. At the same time, sharp-eyed birders can unerringly > distinguish Blackpoll and Pine Warblers at a glance by shape, even though > practically all their measurements, viewed individually in huge samples, > overlap. With regard to terns, I can recognize visually how the length of an > individual's primary projection compares to the chord of its dorsum with > enough precision to distinguish Common and Arctic Terns very confidently. So > I would caution against categorically dismissing this line of evidence. > > Second, the true statuses of non-breeding seabirds remain an amazing mystery, > and the few glimpses we've had so far have been really exciting. Most > obviously, the local status of Arctic Tern has been completely re-written in > the past 20 years based precisely on attention to loafing flocks of > non-breeding terns. Furthermore, scrutiny of these flocks has yielded many > other rarities, some of them as unexpected as longipennis might seem: Elegant > Tern, Cayenne Tern, acuflavidus Sandwich Terns during June, Little Gulls > during June, etc. My point is that although the improbability of longipennis > needs to be answered with strong evidence, much stranger things have > happened. I still examine every Arctic Tern I see with the remote potential > of Antarctic Tern in mind; the non-breeders hang out together down there, so > maybe a few stick together up here, too. Ditto for examining first-summer > Least Terns for Littles and first-summer Black Terns for White-winged and > Whiskered. > > Brian Patteson recently saw a Tahiti Petrel off of Hatteras! > > Shai Mitra > Bay Shore > > > ________________________________________ > From: bounce-122637763-11143...@list.cornell.edu > [bounce-122637763-11143...@list.cornell.edu] on behalf of Joseph DiCostanzo > [jdic...@nyc.rr.com] > Sent: Thursday, June 14, 2018 9:08 AM > To: Robert Lewis > Cc: nysbirds-l > Subject: Re: [nysbirds-l] Dark billed, dark legged Common Terns on Long Island > > Bob, > > Molt, (and I am including change in soft part colors such as bill and leg > color under the term “molt”) is hormonally controlled. There is also > considerable variation between individuals in the timing of molt. The timing > and sequence of molt is no where as neat and fixed as many references might > lead you to believe. Having worked extensively with a banded population, > where the age of individuals is known from their banding histories, I know > how much variation there is. I have seen birds with extensive white foreheads > (or heavy speckling) and extensive carpal bars that I knew from their bands > were two years old. I have also seen two year olds that were > indistinguishable from normal adults. I have also seen that I knew were > three, or four years old (or older based on their bands) that showed speckled > foreheads and traces of carpal bars. I have seen adults in August at the > breeding colony on Great Gull Island that were already in full winter plumage > (black bill, dark legs, carpal bar). Individuals that don’t match the > expected are unusual, but they do occur. > > As for the lack of a carpal bar on these dark billed, dark legged > individuals, you are assuming that feather molt (carpal bar) and soft part > colors (legs and bill) must be in total lock-step with each other. There is > no reason they couldn’t be out of sync in some instances. As for primary > length, this is being based on photos, not actual measurements of the bird in > hand. How is the primary length being assessed? I am guessing versus tail > length. How does anyone know the tail length? > > These dark billed, dark legged Common Terns get reported every year at this > season, just at the time young Common Terns are coming back from South > America. Where are these supposed longipennis birds coming from? The race > breeds in Siberia and winters in the Indian Ocean east to Australia. If > longipennis were going to occur here on the East Coast, the fall seems a more > likely time than the spring migration. It seems far more likely that these > birds are aberrant hirundo retaining aspects of their winter/non-breeding > plumage than that there is an annual movement of Siberian based longipennis > birds through Long Island. > > Joe DiCostanzo > > Sent from my iPad > > On Jun 14, 2018, at 7:59 AM, Robert Lewis > <rfer...@yahoo.com<mailto:rfer...@yahoo.com>> wrote: > > Good points Joe. > > Let's go with the null hypothesis: it's an unusual Common tern (hirundo). > Apparently a Common tern in September can get gray blotches on the > underparts. During the winter they have a black bill, black legs, and a black > cap with white forehead, as first summer birds do now. If it is four - eight > months late in molt (or four months early), maybe that would explain some > features. But then there should be a prominent dark carpal bar. Instead, > there is none. Also, how to explain the very long primaries? And the fact > that the back is a bit darker gray than neighboring Commons, both adult and > immature? > > I found a number of images of longipennis on the web. Here are some screen > shots: > > Index of /lewis/birds/other_long<http://home.bway.net/lewis/birds/other_long/> > > <http://home.bway.net/lewis/birds/other_long/> > > Index of /lewis/birds/other_long > > > > > Bob Lewis > > > > On Wednesday, June 13, 2018, 9:01:37 PM EDT, Joseph DiCostanzo > <jdic...@nyc.rr.com<mailto:jdic...@nyc.rr.com>> wrote: > > > One thing that has to be kept in mind about dark billed and/or dark legged > Common Terns seen on Long Island in the spring is that our Common Terns > (Sterna hirundo hirundo) have dark bills and dark legs in winter (both the > young birds and adults). The possibility that these birds are just S. hirundo > hirundo retaining aspects of their winter plumage must be considered. Indeed, > given the breeding and wintering ranges of S. hirundo longipennis, S. hirundo > hirundo with retained winter characters seems a more likely possibility. > > Joe DiCostanzo > > Sent from my iPad > > -- > > Pasted here 14 Jun 2018 from note to NYSBirds 8 June 2018: > > Subject: Nickerson Beach - Possible Common Tern (longipennis) Species - > Comments and thoughts welcome > Date: Fri Jun 8 2018 1:09 am > From: Shaibal.Mitra AT csi.cuny.edu > > > Dear Mike and all, > > > > This is an interesting bird, and well worth careful discussion. The photos > are, as is so often necessarily the case, not ideal for assessing wing > pattern and structure, and several other features. To my eye, the combination > of adult-like plumage, darkish bill, not so dark legs, and not very deeply > gray underparts is consistent with an early season variation of adult hirundo > Common Tern that we do see from time to time. > > > > The jury is certainly still out on the status of longipennis Common Terns on > the east coast, and in the past I have eBirded the ones I've seen under > regular "Common Tern"--but with lots of notation and documentation. Based on > the checklists you've linked from Jay and Michael, provisionally specifying > this form, I agree it might be best to take this approach while we work > things out. At least it would be easier to collect and access the evidence. > > > > Anyway, two of the best (and earliest in NY) candidates for longipennis were > birds at Cupsogue on 26 Jun 2011 and 24 Jun 2014. I've aggregated photos of > these at the following link: > > > > https://flic.kr/s/aHskD7WtGd > > > > As you will see, these birds were not only different in soft parts colors and > plumage from same-aged hirundo COTE, but also different in terms of structure > and molt (as explained in part in the note to this listserv from 27 Jun 2011, > copied at the end of this note). > > > > I've seen a few more also, including these two I was able to find quickly > just now: > > > > https://ebird.org/view/checkli... > > https://ebird.org/view/checkli... > > > > It seems odd that the best candidates have always been second-summer (TY) > birds, but there are two points worth emphasizing on this front. First, > subadult terns are definitely proven to be prone to wander; second, these > longipennis candidates differ very strongly in multiple ways from the range > of variation I've documented in same-aged hirundo COTE over the past 20 > years. The links in my copied email are long defunct, but I can direct those > who are interested to long series of images of TY hirundo COTE from our area. > > > > Shai Mitra > > Bay Shore > > -- > > NYSbirds-L List Info: > http://www.NortheastBirding.com/NYSbirdsWELCOME.htm > http://www.NortheastBirding.com/NYSbirdsRULES.htm > http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm > > ARCHIVES: > 1) http://www.mail-archive.com/nysbirds-l@cornell.edu/maillist.html > 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L > 3) http://birding.aba.org/maillist/NY01 > > Please submit your observations to eBird: > http://ebird.org/content/ebird/ > > -- > -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME.htm http://www.NortheastBirding.com/NYSbirdsRULES.htm http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/nysbirds-l@cornell.edu/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L 3) http://birding.aba.org/maillist/NY01 Please submit your observations to eBird: http://ebird.org/content/ebird/ -- This communication and any attachments are intended only for the use of the individual or entity named as the addressee. It may contain information which is privileged and/or confidential under applicable law. If you are not the intended recipient or such recipient's employee or agent, you are hereby notified that any dissemination, copy or disclosure of this communication is strictly prohibited and to notify the sender immediately. -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME.htm http://www.NortheastBirding.com/NYSbirdsRULES.htm http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/nysbirds-l@cornell.edu/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L 3) http://birding.aba.org/maillist/NY01 Please submit your observations to eBird: http://ebird.org/content/ebird/ --
