29 July 2013

Variation in Juvenile Ring-billed Gulls (Part 1)

Juvenile Ring-billed Gulls (Larus delawarensis) are quite distinctive within their range, but anyone who's ever spent a little time observing this age group quickly comes to the realization that characterizing a "typical" youngster is no simple task.

The late Claudia Wilds felt that Ring-billeds show the least amount of geographical variation of all North American gull species. Although the various populations across North America bear close resemblance, Wilds' statement should not be understood as a lack of intraspecific variation in juvenile plumages. Indeed, this is generally true with many monotypic gull species as they arguably appear to come together and show less variation as definitive adults.

With this in mind, I feel the literature has put little emphasis on what I've found to be an impressive array of aspects found in juvenile Ring-billed Gulls. Is this variation a known and accepted phenomenon or is it taken for granted?

Juvenile Ring-billed Gulls. Both photographed in Chicago, IL on 26 July 2013.
In this post, I attempt to describe 2 juvenile types that may be thought of as opposite points along a spectrum. Although somewhat cursory, it's my hope that this proposed spectrum will drive others to examine this age group in more detail. The following examples are limited to individuals thought to be from one to three colonies near the Chicago lakefront (all within an approximate 15 mile radius). Fledglings in this region begin to appear in late June and peak in late July.

Two Types:

Ghost-type (1) - As the name implies, this aspect is notably pale with a strong white ground color. The underparts, head and neck tend to show limited brown washing. The scapular feathers usually show an indistinct pattern. They're often boldly edged and based with white, giving the brown centers a golden appearance. The tertials can show a considerable amount of white, especially closer to the tips and along the edges, and the primaries are more likely to show pale tips; Both of these feather groups can show an intricate pattern of dark subterminal diamonds surrounded by white notches. 
Juvenile Ring-billed Gull (ghost-type). Chicago, IL. 26 July 2013.
An extremely pale individual. Note the overall white ground color and limited brown wash to the underparts. The scapular feathers are small and indistinct. The tertials show a striking amount of white and most of the visible primaries are also tipped with white.
Juvenile Ring-billed Gull (ghost-type). Chicago, IL. 26 July 2013.
This pale individual shows more brown on the tertials. Note the notched pattern to the tips. The primaries also have dark subterminal tips in the shape of a diamond, surrounded by white notches.
Juvenile Ring-billed Gull (ghost-type). Chicago, IL. 27 July 2013.
A crisp individual with more neatly patterned upperparts. Note the boldly white-tipped tertials with white subterminal notches and similarly patterned primary tips.

Brown-type (2) - The general appearance of this type is a dark, chocolate-brown aspect. The most distinctive feature of this group is the large scapulars with solidly dark centers. The tertials are mostly plain and resemble the scapulars but are often a few shades darker. The greater coverts are more likely to show an even silver-gray throughout. The primaries are less often tipped with white compared to ghost-types. The underparts, head and neck show varying degrees of dark wash (this feature varies considerably and might be influenced by fading, wear and the onset of the first prealternate molt). Finally, I would suggest that this group is more likely to first acquire gray post-juvenile scapulars and upperwing coverts in late summer.

Juvenile Ring-billed Gull (brown-type). 16 June 2012. Tinley Park, IL.
A typical brown-type with prominent scapulars showing plain and solid dark centers. The tertials are plain and the greater coverts are dressed in gray. Note the early date on this individual.

Juvenile Ring-billed Gull (brown-type). Chicago, IL. 26 July 2013.
Much like the bird above, this brown-type also shows large dark centers on the scapulars. The tertials are plain and are a few shades darker here. The greater coverts are mostly gray. Also note the lack of any notable white edging to the primaries.
Juvenile Ring-billed Gull (brown-type). Blue Island, IL. 04 July 2013.
As expected on this type, the scapulars are relatively large-looking with solidly filled brown centers. The tertials are plain and may appear a few shades darker than the remaining upperparts. The greater coverts show a blend of silver-gray. On average, the primary tips are less likely to have white tips when compared to ghost-types.
An important note here is that the aspects of these plumages quickly become altered shortly after the summer months due to the expected consequences of wear, bleaching and the commencement of the prealternate molt.

The patterns that I've described above are based on my own personal observations from the last four summers. A mixture of characteristics from both types is commonly found on some individuals. I should reiterate that these two types appear to be on opposite ends of a variable spectrum- a spectrum that should be thought of as a work-in-progress.

24 July 2013

Another Lesson in Angle-to-Observer

To most of us, it's clear that lighting can have damaging effects on our identifications. It's a lesson that's soon learned when looking at the upperparts of adult-like gulls on sunny days. Take for example this group of Bonaparte's:

First summer (2nd cycle) Bonaparte's Gulls with similar aged Little Gull. Sheboygan, Wisconsin. 14 July 2013.
The Bonaparte's on the far left looks paler than the other five. Does it suffer from a pigmentation condition that's yet to be explained by ornithologists? Of course not. It happens to be the only individual (along with the Little) that is almost exactly parallel with the camera lens (i.e., the observer). The other five Bonaparte's are all facing towards the observer's ten-o'clock. A slight change in this so-called angle-to-observer can dramatically change our perception of the grays we're seeing. The effect is multiplied on sunny days.

Now note how this "pale" Bonaparte's becomes consistent with the group, altering its upperparts to match the others after changing its angle-to-observer:

Understandably, the Little Gull, which is not significantly paler than Bonaparte's (as the photo suggests) is blown out and overexposed. After waiting a few seconds for it to face towards the observer's ten-o'clock the effect is reversed:

Here the Little Gull appears at least one shade darker than the Bonaparte's which is not accurate (Kodak Gray Scale actual values: Little Gull 4.5-5.5, Bonaparte's Gull 5-6).
Now for an example with non-gray feathers. Consider this collage of the same bird. The images were taken one second apart with no post-processing alterations whatsoever:

Juvenile American Herring. New Buffalo, Michigan. 17 November 2012.
Although probably without any serious implications for identification, the face on the lower image is now darkened (or shall I say the face on the bird in the top image is now lightened?). Kenn Kaufman's reaction to this set verified my point with precision: "This is an outstanding example of the ways in which a single photo (or even a short series of photos) can be misleading...I'm dismayed when I see people arguing strongly for a difficult ID on the basis of a single shot; it's so hard to be sure which "field marks" are real and which are photographic illusions".

Arctic Gull Specimens at CAS

I visited the Chicago Academy of Sciences the other day (twice this month) to review, yet again, a very important Western Gull specimen taken in Chicago, 1927. After finishing up with that work, I took some time to look over a few "fun" skins...

First cycle Ross's Gull (left) with similar aged Black-legged Kittiwake.
The question to ask yourself is how one would tell the Ross's from a Little Gull in this plumage. Besides the lack of any black on the crown (which may be absent in a minority of Littles), the primary pattern is helpful. With first cycle Little Gulls, the black tips on the mid-primaries tend to merge and form a rather solid black portion to the outer edge of the stacked primaries (Martin Reid describes the dividing edge as a "saw-tooth" pattern). In Ross's, the mid-primaries show black tips that are each almost entirely surrounded in white. This is more or less the difference one would be looking for. Of course in flight the identification should be much easier (if one was mentally prepared to call out a 1st cycle Ross's to begin with). Also of note is bill size. It dawned on me while looking at the two trays of ROGU specimens at the museum that Ross's has a very petite bill - very pigeon-like. Indeed, Ross's bill is notably smaller than Little's.

These two are almost exactly the same exact size and this is how the field guides describe them, each about 12.5 inches in length.

Ross's (left). Sabine's (right).

The Ivory is clearly a juvenile. Interestingly, all of the Ivory specimens (even the adults) had this strong "creamy-yellow" tinge to them. It may be unique to this species post-mortem as I did not notice it with any other white feathers on the other gulls. And yes, Ivory Gull is larger than BLKI.

Black-legged Kittiwake (left) with Ivory Gull.

Now for a group photo of some of the most sought after arctic gulls on the planet:

From left to right: Ross's, Black-legged Kittiwake, Ivory and Sabine's Gull.

All of the specimens were collected in Alaska and off its shores. The Ross's was collected in Barrow in September. Here's a first alternate Ross's Gull collected in Barrow in June:

1st alternate Ross's Gull.
The black necklace is usually obtained by about 10-12 months of age and is not always nicely defined as in alternate adults.

A special thanks to Dawn Roberts for again allowing access to the collection and putting up with my childness while reveling over these skins.

Back to Sheboygan: Gullextravaganza!

Sheboygan Wisconsin's North Point Park is unquestionably one of the premier gulling hotspots on western Lake Michigan in the summer months. Where else can you tally "8" gull species on a mid-summer day? On 14 July 2013, I had the following, all in about 7 hours of working the gull flocks from Kings Park to Deland Park to North Point:
  • 3 Little Gulls (all second cycles, now with primary molt initiated)
  • 2 Laughing Gulls (1 adult type and 1 second cycle)
  • 1 Franklin's Gull (adult type)
  • 1 Great Black-backed Gull (2nd/3rd cycle type)
  • 14 Lesser Black-backed Gulls (12 individuals in one view; photographs confirmed 2 more)*
Of course the three common species were also present in good numbers:
  • 200 Bonaparte's Gulls (most first summer birds, i.e., early second cycle types)
  • 900 Ring-billeds Gulls (a mixed bag of ages with decent numbers of juveniles present)
  • 150 American Herring Gulls (few definitive adults)
*Now a record high for me on Lake Michigan, the 12 Lesser Black-backeds seen together at Deland Park is unprecedented. The increase in summering LBBG on Lake Michigan is becoming a reality much faster than I imagined it would be when putting together my review of this species' status in "Rethinking the Lesser Black-backed Gull in North America" (Birding; V45 N1, pp.34-41).

8 of 12 LBBGs at Deland Park. Most are 1st summer birds in their 2nd molt cycle.
The Little Gulls that have been summering here since late May have progressed nicely with their upperwing covert feather growth and are too in their 2nd molt cycle. Here's one photographed with its bigger cousin:
First summer Little Gull (2nd cycle) with similar aged Bonaparte's Gull. North Point Park. Sheboygan, WI. 14 July 2013.
And a first summer Laughing Gull:
First summer (2nd cycle) Laughing Gull with Ring-billed Gulls. North Point Park. Sheboygan, WI. 14 July 2013.

The gulls here are all mostly feeding on the dying shad that lazily swim near shore. In fact, hundreds were seen dead along the shore, especially on the north beach between the water filtration plant and the "gazebo". The smell was classic "Salton Sea" and I had no objections to this, at all!

Some of our more common species that posed nicely:
First summer (2nd cycle) Bonaparte's Gull.
First summer (2nd cycle) Bonaparte's Gulls.
Juvenile American Herring Gull.
Juvenile Ring-billed Gull (so-called "cinnamon" type).
Finally, I was able to get a good minute's worth of a Little Gull close to shore on video, feeding:

05 July 2013

First Juvenile Ring-billeds of 2013

My wife, the children and I found our first group of juvenile Ring-billeds on the 4th of July this year. As has become our habit for the last few summers, the family and I specifically go looking for juvenile Ring-billeds together in late June and early July - a somewhat peculiar family tradition to your average Joe.

We literally scour local lakes, parks and mall parking lots seeing who can spot a juvenile first. This year we spotted them at the same time. First one, then four, then eight and finally a high count of 11.

Juvenile Ring-billed Gull. Blue Island, IL. 04 July 2013.
Juvenile Ring-billed Gull. Blue Island, IL. 04 July 2013.
Juvenile Ring-billed Gull. Blue Island, IL. 04 July 2013.

My personal earliest "inland" juvenile Ring-billeds is an individual from 16 June 2012, a single bird in mall parking lot in Tinley Park, IL.

03 July 2013

Franklin's with Puzzling Primaries

Of all the world's gull species, Franklin's Gull is the only one that is known to replace all of its feathers twice a year (complete prebasic and prealternate molts). It's said that this phenomenon is more common in adults than in first cycle birds. Seeing a northbound Franklin's in migration, therefore, is somewhat of a unique experience as it provides the observer with an opportunity to asses whether a complete prealternate molt took place on the wintering grounds, or, if the molt is suspended, or never took place at all. Of course the prealternate molt can be ongoing at stopover sites during migration.

Consider this presumed first summer bird. The gray upperwing coverts and tertials are a result of the first prealternate molt. New primaries are also coming in:
Franklin's Gull. LaSalle County, IL. 04 July 2010.

First alternate primaries (P1-P7). Notice the three outer primaries (P8-P10) are juvenile. Most of the secondaries are also juvenile feathers.
The prealternate molt (incomplete here) likely took place on the wintering grounds, and now "appears" suspended. But could it be that this molt is not suspended at all? Franklin's commonly grows out its primaries at a relatively slow rate, fully growing one primary at a time before dropping the next. It could be that this individual is roaming the interior (i.e., south of the breeding grounds) and has resumed its molt. In any case Olsen and Larsson note that primary molt picks up again in July in these first alternate birds.

Now to the puzzle bird that this post's title is referring to:
Franklin's Gull. Chicago, IL. 25 March 2011.
The first 6 primaries are fresh, while the outer four (P7-P10), appear to have worn tips. They certainly look like they're 2nd generation primaries. The gray on the bases of these feathers seems too extensive and adult-like for juvenile feathers, yet the gray tongue tips do not show any sign of a white medial band that would suggest an older bird (less black in the wingtips and more white on the tongue tips is thought to be an age-related characteristic in this species).

After giving the puzzle-bird some thought, I guessed that it may not have molted any primaries in PA1. This is not unheard of especially with birds that winter farther north.

Franklin's Gull with puzzling outer primaries.. Chicago, IL. 25 March 2011.

It may have acquired second generation primaries more or less around the time of the second prebasic molt (1st summer). The older, outer four primaries, would therefore be retained from 2nd basic. The newer primaries, P1-P6 may be 2nd alternate (2nd winter), which presumably were acquired via an incomplete prealternate molt (on the wintering grounds?). Whether or not PA2 is incomplete or suspended is beyond the scope of this post, but it's obvious P1-P6 are newer than P7-P10. It may just be that primary molt will resume with the outer primaries once this bird settles down for the breeding season (just as in the LaSalle County bird above).

The only confusing consequence of my explanation is whether a first cycle Franklin's can migrate to South America and back to North American with its first basic primaries (i.e., its juvenile primaries). One has to wonder whether this bird ever migrated as far south as the majority of Franklin's do during their first winter. Or perhaps it roamed the interior during its first journey back north, never making it to the breeding grounds in the northern Great Plains or the Prairie Provinces.