Hey Tony,
-- Thanks for posting an article on Petrochelidon identification! I have yet to read that piece, so my points on field marks between the two swallows are not in direct reference to it. My opinion on the ID is influenced by countless observations of young and adult Cliff and Cave Swallows in the field, and discussion with other birders.
I'll join in congratulating Steve Mlodinow on his find, who demonstrates over and over again what an exceptional birder he is.
My point here still stands; young Cliff vs Cave Swallow is a very challenging ID with more caveats than most birders realize, so to identify even a previously reported individual should be exercised with utmost caution. I suspect Tony's article illuminates this as well.
Best,
David Tonnessen
On Thu, Aug 20, 2020, 2:02 PM coloradodipper via Colorado Birds <cobirds@googlegroups.com> wrote:
All:--
I wholeheartedly agree with David's main point in his posted... criticism, that main point being that identifying Cave Swallow in Colorado requires utmost caution. However, his post contains numerous inaccuracies that serve only to make the situation more confusing.
It is a rare juvenile Cliff Swallow sporting the "golden/bronze forehead and throat patches" typical of adult Cave Swallow (despite my unfortunate wording in the Cave Swallow paper; see link further below), which is what has been reported recently from John Martin Reservoir. As example, see the large selection of photos in the eBird/Macaulay photo archive of juvenile Cliff Swallows here:
https://ebird.org/media/catalog?taxonCode=cavswa&mediaType=p&q=Cave%20Swallow%20-%20Petrochelidon%20fulva&age=j
Each page of the photo archive is supposed to show 50 photos, though I've never tested that contention, though the number is certainly something close to 50. Regardless, I went through four pages of photos (ignore the occasional mis-aged adult Cliff Swallow photos) without finding a single bird that would have caused me pause in the field. I suspect that if one keeps clicking on the "Show More" link at the bottom of the page, one may get thoroughly tired of the exercise before one finds a photo of a correctly identified juvenile Cliff Swallow that sports a forehead and throat pattern like that of an adult Cave Swallow.
There are multiple factors behind the dis-similarity of appearance of forehead and throat color of juvenile Cliff Swallow to the appearance of adult Cave Swallow, even of juvenile Cave Swallows. The primary one of these is that most juvenile Cliff Swallows have a variable number of white feathers on the head, particularly on the forehead and throat, ranging from just a feather or few to extensive patches of white (not rarely). This tendency is also true of juvenile Cave Swallows (as here). In fact, this presence of white feathers is so frequent in juveniles in the genus Petrochelidon that it is a useful feature in helping to rule out either of those species when looking at juvenile Barn Swallows (genus Hirundo), an all-too-frequent ID stumbling block (see my paper on Barn Swallows in non-adult plumages in the latest issue of Colorado Birds).
For those juvenile Cliff Swallows whose throats are not covered in white feathers, many have throats that are more extensively dark than even the throats of adult Cliff Swallows:
Given the variability in throat coloration and pattern in juvenile plumage of Cliff Swallow, I would not be surprised if there is the odd individual or two whose forehead and throat color and pattern approximated the appearance of that of adult Cave Swallow. However, such birds are almost certainly very rare, possibly rarer than Colorado Cave Swallows.
However, skilled and experienced birders know that single-character identifications can lead to error, and in my paper on juvenile plumages of Cliff and Cave swallows, I twice suggest that using multiple aligning characters to make identifications of juvenile Cliff and Cave swallows is important.
I interpreted Mr. Tønnessen's wording "depending on age" when apparently referring to juvenile Cliff Swallow plumage to mean that their appearance was changing in some significant manner, despite that the plumage has been worn for only a short time by mid-August and that Cliff Swallows molt on the winter grounds. If I read more into that possibly throwaway phrase than was intended, then I apologize to David.
David seemed to take an uncited swipe at my above-linked paper on juvenile plumages of Cliff and Cave swallows when he suggested that my thesis of Cliff Swallows having consistently more and larger dark patches on the lateral under-tail coverts than shown by Cave Swallow was not reliable. While I discovered that ID character while doing the research for that paper, further extensive personal experience with both Cliff and Cave swallows in the field in many parts of the US has made me more certain of the efficacy of that field-ID character when proper precautions about lighting and viewing angle are taken. Are there Cliff Swallows with less-noticeable or even absolutely fewer and less-obvious markings on those feathers? I have no doubt there are, given the variability inherent in the biological process of recombinant DNA that produces organisms like Cliff Swallow and Cutthroat Trout and even that epitome of variability known as Homo sapiens. As I stated in the swallow paper and in nearly countless other ID articles and photo-quiz solutions, relying on a single character is problematic, at best, and decidedly problematic in most situations. Mr. Tønnessen seems to have missed that point, somehow.
I am also amazed at David's selective knowledge when it comes to records of vagrant swallows. While many move on after a short time, quite a few, perhaps many, stay put if they find conditions suitable for such. One such example of which I have personal experience is the Brown-chested Martin in Cape May, NJ, which was found on 6 November 1997 (but may have been present earlier) and was present at least until 15 November, when it may very well have succumbed to the results of a strong cold snap. There are many other instances of vagrant swallows residing at a particularly advantageous location/situation. Given the very large number of swallows that have been reported from northwestern John Martin Reservoir in recent days, I suggest that the situation is particularly advantageous enough to encourage individual swallows to stay for extended periods.
It is unfortunate that the situation/location whence the recent Cave Swallow (or swallows) reports originate does not enable obtaining spectacular photos that permit quick and certain ID. It is equally unfortunate that some of the photos show individuals that are certainly Cliff Swallows (or, possibly, Cliff x Cave Swallows). However, I have seen photos from three photographers that seem to nail the case for the ID of Cave Swallow. Yes, they're not perfect, but, in toto, in my opinion, they make the case, particularly Nathan Pieplow's extensive selection.
Congratulations to Steve Mlodinow for finding and reporting his second Cave Swallow in the state (yes, he found the state's first record, too!) and to the birders that put in the time and effort to document this occurrence in subsequent days. I'm just sorry that I was not able to manage that feat, as my party and I were not able to find the bird or birds on our visits.
Sincerely,
Tony
Tony Leukeringcurrently between residences, but still in CO
P.S. The English pronouns "who" and "whom" are intended to refer solely to that epitome of variability, Homo sapiens.
-----Original Message-----
To: Digest recipients <cobirds@googlegroups.com>
Sent: Thu, Aug 20, 2020 2:20 am
Subject: [cobirds] Digest for cobirds@googlegroups.com - 8 updates in 7 topics
"David Tønnessen" <davidtonnessenx@gmail.com>: Aug 19 06:20PM -0600
Good afternoon, Colorado birders.
I want to issue a word of caution when identifying swallows of the genus
Petrochelidon (Cliff and Cave Swallow as we know them in English). In June
through at least early September, millions upon millions of young Cliff
Swallows whom have not fully attained adult plumage are migrating south
through the Great Plains, where a sizeable percentage of this species'
total population breeds. Because these young birds sport golden/bronze
forehead and throat patches of the same color and of varying shades
depending on age, they are extremely difficult, if not impossible at times
to distinguish from young or adult Cave Swallows. They also show a stronger
buffy wash in the underparts than adults, and the undertail coverts are
often very weakly marked, two features often incorrectly associated with
just Cave Swallows. Some sources that should demonstrate this well are
Sibley and better yet, eBird's Macaulay library. Over this last week, I
would have given almost anything to have photographed the fencelines upon
fencelines of young, variable Cliff Swallows I observed over the summer, so
I could better demonstrate my point.
So please, when reporting a Cave Swallow in Colorado, provide excellent
photographic or auditory documentation. This post is not meant to disparage
or discredit initial reports of Cave Swallow at John Martin Reservoir.
However, knowing the tendency of swallows, if there was a Cave Swallow at
John Martin at some point, the chances of it sticking around for several
days at the same spot seem slim. All of the photos I've seen reported as
Cave Swallow from the location have either been poor and inconclusive, or
have been nice photos of an immature Cliff Swallow.
Happy finding and documenting rarities, and stay smart and healthy in these
times.
David Tonnessen
Colorado Springs
You received this message because you are subscribed to the Google Groups "Colorado Birds" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cobirds+unsubscribe@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/1873873465.3880376.1597953719496%40mail.yahoo.com.
You received this message because you are subscribed to the Google Groups "Colorado Birds" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cobirds+unsubscribe@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/CADkL8Fc%2ByecPAEANkU2d-nbUsbL%2B5s8Chs_PGxw5xNdo7WEU_g%40mail.gmail.com.
No comments:
Post a Comment