27 December 2010

Kumlien's or Iceland?

The subspecies of Iceland Gull (L.g. glaucoides) that regularly occurs in North America is Kumlien's Gull (L.g. kumlieni). All sightings of Iceland Gull in North America should first default to Kumlien's based on range.

Range map of Kumlien's Gull (L.g. kumlieni); Red: breeding, Blue: nonbreeding

North American sightings of the nominate race glaucoides are an exception to the rule. It is thought that the nominate race is observed yearly in eastern Newfoundland, with a ratio of perhaps 1:1000 glaucoides to kumlieni in St. John's (per comm. Dave Brown). There are multiple records of adult glaucoides from New England but it is difficult to verify the validity of these records since they lack detailed assessments of upperpart coloration. My discussion here is with respect to adults only as subadults have proven to be much more difficult to identify to subspecies and some known age birds have been known to "swap" identities with maturity (Charles).

The question we need to ask in the United States is not whether glaucoides can stray into the lower 48 states, but rather, can it be distinguished from the regularly occuring Kumlien's? Most adults are easily distinguished since the majority of Kumlien's show some darker gray tones to the outer webs of  the outer primaries. The confusion arises in what Steve Howell has called "stage zero" Kumlien's Iceland Gulls. These are adult individuals with pure white wingtips that mimic the appearance of nominate glaucoides.

The distinguishing features of glaucoides include a paler-mantle (Glaucous Gull coloration) and a pale lemon-yellow iris in all adult stages. It should be noted that mantle shade is difficult to ascertain without side-by-side comparisons of benchmark species; this is another reason why North American observers must be cautious when considering the nominate race. Other supporting features on glaucoides include a rounder and more gentle look to the head with a bill that is typically smaller than Kumlien's - but there are varying degrees of overlap.

Here is an adult Kumlien's Gull (front) shown with an adult American Herring Gull. Could you think of at least 2 reasons why this isn't a nominate glaucoides?

Chicago, IL; 26 Dec 2010
The first thing to notice is that this individual has a dark iris and the mantle appears to be very close to the shade of the Herring Gull's upperparts. Also, the outermost primary shows a thin frosty-gray subterminal mark. Howell would classify this wingtip pattern as "stage one" and it's helpful in ruling out any suspicions of a nominate Iceland Gull. Another thing that I notice in this photo is a sloping forehead which is not often found in glaucoides.

In my opinion, Iceland Gull (L.g. glaucoides) is one of the most beautiful gulls of the Holarctic. Any report of this race in North America should be scrutinized with care; sightings should be well documented with photographs, preferably next to other species that can be used for comparison.

Charles, D. 'Identification challenges presented by 2nd winter Kumlien's Gull'. IRBC Gallery Notes.
Dunn, J. & Howell, S.N.G. 2007. Gulls of the Americas: 462-470.
Howell, S.N.G. & Mactavish, B. 2003. Identification and Variation of Winter Adult Kumlien's Gulls. Alula 9(1): 2-15
Olsen, K.M. & Larsson, H. 2004. Gulls of North America, Europe, and Asia (reprint).
Zimmer, K.J. 1991. Plumage Variation in Kumlien's Iceland Gull. Birding XXIII(5): 254-269

26 December 2010

1st Cycle Herring Gull

I found this American Herring Gull at Miller Beach in Gary, IN on 22 December, 2010.

My initial impression was perhaps a delayed 2nd cycle bird because of the combination of the gray scapulars, bleached head and neck, and the pale coloration to the bill. The basal part of the bill seemed a bit too pale for a 1st cycle in December. 1st cycle Herrings usually, but not always, retain more black in the bill in the early part of the winter season; some will have the basal 2/3 of the bill completely pale with just a black tip.

The head on this bird is bleached along with parts of the neck and chest - a look that's not really expected in early winter. After a closer look at the upperwing coverts, a pattern that's much more consistent with a younger bird is revealed. 2nd cycle individuals have a finer pattern to the greater coverts or sometimes show signs of abrasion and fading. I waited a few minutes and watched it take wing. It became obvious that the flight feathers were those of a juvenile in its first molt cycle. This individual is probably no more than 6 to 7 months old.

I think it's safe to say that this gull has undergone a moderate to accelerated post-juvenile molt of the scapulars, but there's still several obvious juvenile scapular feathers showing (even in the photograph of the bird standing). The head and neck area have likely whitened by bleaching but there's also the possibility that some head, neck and chest feathers are being replaced by the initiation of the 1st prealternate molt.

Here is a more typical 1st cycle Herring for mid-late December:

Note the almost entirely black bill that is just starting to show pale markings. The scapulars have a few new gray feathers but not predominating, and the head and neck are not bleached as the individual above. Both of these birds were photographed minutes apart at Miller Beach.

Knowing what a particular aged American Herring Gull should look like in any given month of the year is not an easy task. The variation in appearances will always offer the keen observer something worthy of pause. It's important to realize that there's an expected array of "aspects", for instance, with 1st cycles in early winter, mid-winter and late winter. Learning these limits of variation for species like Herring Gull are, in my opinion, foundational for anyone that has a serious interest in North American gulls.

13 December 2010

A Quick Word on Hybrid Gulls

If you’re a gull enthusiast, then you recognize the great propensity for gulls to hybridize - especially the large white-headed gulls. I remember a time not too long ago when I approached every hybrid gull with a sense of urgency and the feeling that there must be one correct answer to the identification. Much of this rigid approach where notions are only perceived in black and white is unquestionably rooted in naivety. I’ve come to accept that many - if not all - hybrid identifications are tentative and to a great degree nothing more than “educated guesses”. These educated guesses are based on inferences that are derived from our experience with the presumed parent species. Some of these identifications could be very convincing and more plausible than others, but this I imagine comes with a great deal of experience and knowledge. I could proudly say that I’ve become more and more reluctant to resolve hybrid IDs with words such as “surely”, “certainly” and “definitely”. Some exceptions can be made for known phenomena hybrids such as Olympic Gulls (Western X Glaucous-winged), but a level of uncertainty is presented in some of these individuals as well.

I find it interesting that there are usually 2-3 differing opinions offered by birders as to the origins of a hybrid. I feel it’s very beneficial to scrutinize the counter arguments presented by others and to try to see what features and marks they’re picking up on that I may have overlooked. I’d like to suggest that the process of assessing a hybrid should be more important than assigning a name. I've found that assessing hybrids helps me reinforce a lot of what I know about the presumed parent species and I almost always learn something new during the process. For some, thinking about hybrid gulls in this manner is maddening; I think this is mainly because having to apply higher level thinking skills without arriving at a conclusive ID seems like a wasted effort for some birders. After all, most of us took up birding so that we could relax. Unfortunately, these birders demand a name for every individual they encounter in the field and this, I’ve learned through personal experience, is an imprudent expectation to have of nature. Nature is not always tabulated in Systema Naturae. I think the sooner one’s thinking "evolves" to this reality, the sooner hybrids become more enjoyable.