May 30, 2017

It's coming up on that time of year...

Summer time is approaching and all the lingering sub-adult gulls are beginning to molt. This is the time of year when even the most dependable of field marks will fail us for some individuals.

Feathers wear out. Most birds replace their flight feathers once a year and their body feathers at least once (in many species twice) in a year. In gulls however, birds hatched last year actually end up keeping their feathers for up to a couple months longer than a calendar year. Most immature gulls we see now fledged at the end of June last year, but their molt cycle usually begins in July and August. The previous year’s juveniles always show more feather wear by midsummer than older birds.

Gulls do not replace all their flight feathers at once. They molt sequentially, beginning with the innermost primaries.

The process of replacing all the flight feathers takes weeks and while molt is going on, some birds can look pretty sad. The time lag between those first new feathers and the last ones is significant enough to show as uneven wear of the flight feathers of older birds when compared to fresh juveniles which grew in all their flight feathers at once. A juvenile’s feathers wear out all at once, too, and that’s partly why some look so sad and ratty this time of year.

So, why don’t all these young molting gulls look equally awful?

There are many things that contribute to feather wear: sun, dirt, bacteria, avian parasites, not to mention day to day use. But the single most important mitigating factor in comparative feather longevity is the presence or absence of feather pigments collectively known as melanins. There are two general classes of melanin. Eumelanins which produce blacks and grays and Phaeomelanins which produce browns and reddish colors. Eumelanins add to the structural integrity of flight feather which is most probably why large, flight dependent birds routinely have black wingtips. Melanins may also promote drying of feathers by absorbing radiant heat and there is some evidence that melanin may also inhibit bacterial degradation of feathers.

If we compare the wear patterns of feathers molted from older birds to those of the younger ratty looking birds the effects of melanin can be seen.

Note, for example, only the white primary tips have worn away in the feathers (right side) of older birds while the feathers from younger birds (left side) are worn back to sharp, frayed points.

So, the bottom line is that gull identification can be harder than usual in the molting season and even the hardcore lariphiles may get stumped by some of the more scrappy-looking individuals. There is never any shame in defaulting to gull sp.

References

Gill, F.B. 1989. Ornithology. W.H. Freeman and Co., New York.

Howell, S.N.G. and J. Dunn. 2007. Gulls of the Americas. Houghton-MifflinCo., Boston.

Howell, S.N.G. 2010. Molt in North American Birds. Houghton-MifflinCo., Boston.

Pyle, P. 2008. Identification Guide to North American Birds, Part II. Slate Creek Press, Point Reyes Station, CA.

Winkler, David W. 1996. California Gull (Larus californicus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/259

Melanin in Wikipedia http://en.wikipedia.org/wiki/Melanin

Modified from an article written by Mike Patterson originally posted at: http://www.surfbirds.com/community-blogs/northcoastdiaries/?p=1575

Posted on May 30, 2017 13:45 by mikepatterson mikepatterson | 0 comments | Leave a comment

March 10, 2017

Thayer’s ain’t so, Joe

BREAKING NEWS [03/29/2017]: The new list of NACC proposals is out and proposal 7 (page 29) is to lump Thayer's Gull...
http://checklist.aou.org/assets/proposals/PDF/2017-C.pdf

One cannot spend time sorting through gulls without, at some point, falling into the black hole that is the Iceland/Kumlien’s/Thayer’s puzzle. A few years back I suggested (to nobody’s amusement, but my own) that the complex be renamed Schrödinger’s Gull. On purely technical grounds, the issue is more about observational relativism than it is quantum uncertainty, but Schrödinger’s has a nicer ring to it and gets to the random heart of the problem in a way that Einstein’s Gull does not. But I digress…

If one sees a member of this complex in Europe, things are pretty straightforward. It’s an Iceland Gull. Here in North America things get more complicated. East Coast birds are (most of them anyway) considered to be the Kumlien’s form of Iceland Gull which has (on average) grayer primary tips than European forms. To the West, there is the much darker Thayer’s Gull which has a more complicated taxonomic history and requires a bit of backstory.

For those of you old enough to remember, Thayer’s Gull used to be considered a subspecies of Herring Gull. Two studies led to the split that gave Thayer’s Gull its independence. The first was by A.H. Macpherson [1961. Observations on Canadian Arctic Larus gulls, and on the taxonomy of L. thayeri Brooks. Arctic Institute of North America Technical Paper 7:1-40] which demonstrated that there was positive assortment to species in areas of sympatry between Herring and Thayer’s Gulls. The second was a more controversial (to be polite) study done by N.G. Smith which was eventually featured in Scientific American [1967. Visual isolation in gulls. Scientific American 217(4): 94-102]. Smith’s work showing assortment has never been replicated and other studies would seem to contradict many of his conclusions. Some within the ornithological community have even suggested that he faked his data. Having read through Smith’s original publications and subsequent critiques and rebuttals, I have reached the personal conclusion that the study has flaws, but the primary problems were observer bias (especially among his locally sourced assistants) and inadequate sample size, not fraud. Much like the current problem with sorting Thayer’s from Kumlien’s in the field, Smith saw what he (and probably his major professors) expected to see and there were no independent controls to rein in the biases.

But that was 50 years ago. What about now? Surely modern cladistics and the genetics revolution can get us to the truth. Not so fast. There are several competing hypotheses for the taxonomic state of things beginning with the current American Ornithologist’s Union (AOU) model which holds Thayer’s as a separate species and Kumlien’s as a subspecies of Iceland. Most of these hypotheses can find at least one champion among the cladists. So, hypothetically, we could say one of the following:

1. Thayer’s is a separate species and Kumlien’s is a recognizable subspecies of Iceland.
2. Thayer’s, Kumlien’s and Iceland are three species with fuzzy distributional edges.
3. Thayer’s and Iceland are separate species and Kumlien’s is a hybrid (the fuzzy middle) between the two.
4. Thayer’s is a subspecies of Iceland and the differences represent a cline of variation from east to west.

There are additional sub-hypotheses regarding the taxonomic value of sorting populations into subspecies and/or clinal subpopulations without usefully discrete phenotypical or ecological boundaries.

No one goes for hypothesis #2 much these days. The clinality (if that’s a word) of characters between Kumlien’s and Iceland have been well established in multiple studies. The clinal relationships between Thayer’s and Iceland forms are less clear-cut and are best described as blotchy. Intermediate gulls are debated ad nauseum and there is a decided east coast vs west coast bias among identifiers regarding what constitutes dark enough to be Thayer’s or light enough to be Kumlien’s. Blotchy is the best way to describe their genetic relationships as well.

In general, most Northern White-head Gulls show confusing genetic relationships [J.-M. Pons, A. Hassanin, P.-A. Crochet, 2005, Phylogenetic relationships within the Laridae (Charadriiformes: Aves) inferred from mitochondrial markers. Molecular Phylogenetics and Evolution 37 (2005) 686–699], so making taxonomic claims based on genetics is problematic, especially among the very closely related members of the Iceland Gull Complex. It has even been suggested that there may not be enough consistent genetic variation in the entire Large White-headed Gull clad to justify any of them being separated into species.

Lumping all larids is probably not going to happen anytime soon, but the tide of scientific opinion is running against Thayer’s Gull as a discrete biological unit. Most European ornithological groups have already lumped Thayer’s into the Iceland complex. The AOU is the last big holdout. I see a time in the not too distant future when we will see this complex lumped into a single, highly variable species and arguments about Thayer’s vs Iceland will become a thing of the past (for non-academic folks, anyway).

Posted on March 10, 2017 15:15 by mikepatterson mikepatterson | 1 comments | Leave a comment

February 21, 2017

The Olympic Gull

Gulls of one particular species will, if given the opportunity, hybridize with gulls from a different species. The literature is full of examples of intermediate forms between gull species and many of these intermediates occur regularly enough that they have been given their own vernacular names. Most of these hybrid forms occur at the boundaries between the ranges of two parent species. Overlaps between breeding boundaries are called zones of sympatry. One of the best known and best studied of these zones occurs in the Pacific Northwest where the breeding ranges of Western Gull and Glaucous-winged Gull overlap. The resulting hybrid is called the Olympic Gull.

A study done in 1996 by Douglas Bell showed that, in the region between the Columbia River and the tip of the Olympic Peninsula, birds showing some degree of introgression outnumbered birds of clean Western or Glaucous-wing phenotypes during the breeding season.

Bell1994

These hybrid individuals are just as fertile as their parents. Hybrids mate with Western Gulls. Hybrids mate with Glaucous-winged Gulls. Hybrids mate with hybrids. This creates a continuum of variation from dark to light. There is no one single phenotype that constitutes "Olympic Gull" and, from a purely statistical point of view, the average gull one sees during the breeding season on the Washington Coast is likely to be a hybrid - even the ones that are Western looking or Glaucous-winged looking. When I'm asked to identify these birds by folks from out of town I'll often say "that's a mostly Western Gull" or "that's a mostly Glaucous-winged Gull." On eBird I lump them as Western/Glaucous-winged.

Things change a bit in the winter when gulls disperse away from their breeding grounds. One can find strikingly obvious Glaucous-winged Gulls, presumably down from Alaska, or crisply dark Western Gulls, up from the south.

So, how should we sort them here? I have guidelines which you all are under no obligation to follow:
Glaucous-winged Gulls should be pale and the primary tips should be pretty close to the same shade of gray as the back, lighter in younger birds as the feathers wear.

Western Gull 3rd winter birds and adults should show black primaries, not gray, not slaty, just black. 2nd Winter birds should have a dark back and very dark, nearly black primaries. 1st winter birds? Unless they are really dark, I punt to Western/Glaucous-winged....

Posted on February 21, 2017 22:59 by mikepatterson mikepatterson | 2 comments | Leave a comment

January 19, 2017

The Ugly Gull...

A while back I started using the term "ugly gull" to describe any gull that presented to me an identification challenge. Hardcore lariphiles took umbrage. Gulls are not ugly. Hardcore lariphiles have no sense of metaphor. A gull can be physically beautiful and still be ugly to parse.

While I would not describe myself as a passionate gull person, I am a realist. The gulls are out there. They represent an important component of many ecosystems. And sometimes, on a cold and rainy winter's day, they're the only game in town. Gulls, as a taxonomic group, sit in that evolutionary gray area where genuine physical and behavioral differences are often clearly discernible, but the genetic differences are muddy and contradictory. Speciation baby! It ain't nearly as pretty as we might think.

So, sit back and enjoy the ugly gulls. Some may get named. Some may not. But the game is addictive and it will keep you off the streets.

Posted on January 19, 2017 20:58 by mikepatterson mikepatterson | 2 comments | Leave a comment

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