Perhaps I missed it, but there seems to be an obvious question here: have
bids like this been reported from neighboring states?
Bob LewisSleepy Hollow Y
On Thursday, June 14, 2018, 10:49:25 AM EDT, Shaibal Mitra
<[email protected]> 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: [email protected]
[[email protected]] on behalf of Joseph DiCostanzo
[[email protected]]
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
<[email protected]<mailto:[email protected]>> 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
<[email protected]<mailto:[email protected]>> 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
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