28 December 2016

Banded 1st & 4th Cycle American Herrings

A couple of more known-age, known-origin Herrings to close the 2016 calendar year.

Kane County, Illinois. 22 December 2016.

At the end of its hatch year, this 1st cycle shows complete post-juvenile scapular molt. This appears to be a typical molt state for our Great Lakes Herrings, sometimes taking place by early to mid-September. A single lesser upperwing covert has been adventitiously replaced.

Band number: 1176-41708. Banded as a flightless chick on 19 June 2016. Door County, WI.

In its first "adult" plumage, this 4th cycle (i.e., 4th basic plumage) cooperated for a full band read.
Band number: 1106-27454. Banded as a flightless chick on 25 June 2013. Door County, WI.

The underwing pattern shows extensive black, even for a Great Lakes Herring.

P10 mirror is relatively small and does not extend across the entire outer web. P4 shows a distinct spot on the outer vane, something shown by a minority (< 15%) of the adult type Herrings I see.

The most telling sub-adult-like feature is the marked outer greater primary coverts. We regularly see individuals like this and assume they are young adults. Such an assumption appear to be generally true.

30 November 2016

Monthly Notables November 2016

    • Black-legged Kittiwake (adult). Pueblo County, Colorado. 01 November 2016.
      • Continuing from last week of October.
    • Little Gull (adult). Union County, Indiana. 03 November 2016.
    • Black-headed Gull (adult). Accomack County, Virginia. 05 November 2016.
    • Yellow-legged Gull (adult). St. John's County, Newfoundland. 06 November 2016.
      • Continuing.
    • Thayer's Gull (adult). Nome County, Alaska. 06 November 2016.
      • Late. Very rare. 13th Fall Record for Nome.
    • Black-legged Kittiwake (juvenile). Lake County, Minnesota. 07 November 2016.
    • Laughing Gull (adult type). Mahoning County, Ohio. 07 November 2016.
    • Sabine's Gull (juvenile). Ketchikan Gateway County, Alaska. 09 November 2016.
      • Late. First November record for Ketchikan.
    • Lesser Black-backed Gull (2nd cycle). Portage la Prairie Area Co, Manitoba. 10 November 2016.
      • Continuing from June 2016.
    • Lesser Black-backed Gull (adult). Santa Clara County, California. 10 November 2016.
    • Western Gull (1st cycle). Salt Lake County, Utah. 11 November 2016.
      • Continuing from October 2016.
    • Black-legged Kittiwake (juvenile). Palm Beach County, Florida. 12 November 2016.
    • Ring-billed Gull (adult). Juneau County, Alaska. 13 November 2016.
    • Great Black-backed Gull (adult). Pueblo County, Colorado. 18 November 2016.
      • Believed to be the same returning adult for the 23rd year!
    • Glaucous Gull (juvenile). Power County, Idaho. 19 November 2016.
    • Vega Gull (adult). Santa Clara County, California. 22 November 2016.
      • Photos of a very promising individual with all the correct field marks. No open wing.
    • Slaty-backed Gull (adult type). St.John's County, Newfoundland. 23 November 2016.
    • Little Gull (1st cycle). Ventura County, California. 23 November 2016.
      • 3rd county record. First in 27 years for Ventura County!
    • Sabine's Gull (juvenile). Haines County, Alaska. 23 November 2016.
      • Late.
    • Slaty-backed Gull (adult). Pierce County, Washington. 24 November 2016.
      • Reoccurring at this site.
    • Iceland Gull (1st cycle). Salt Lake County, Utah. 24 November 2016.
      • Apparent Kumlien's Gull.
    • Lesser Black-backed Gull (adult). Riverside County, California. 26 November 2016.
    • Slaty-backed Gull (3rd cycle). Metro Vancouver County, British Columbia. 27 November 2016.
    • Black-headed Gull (adult). Butler County, Pennsylvania. 29 November 2016.
      • Presumably returning to this site since 2008.

    Miscellaneous Notes.
    1. Reported early this month was an intriguing 1st cycle bird from Superior, Wisconsin (observed in September). Plumage entirely juvenile. Body size, bill size and structure all seemed perfect for Ring-billed Gull which it was associating with. However, the inner primaries and greater coverts were plain and uniformly dark like a Lesser Black-backed Gull (and this is what the observers initially identified it as). After some discussion on North American Gulls (NAG), the bird was thought to either be a RBGU x LBBG or a melanistic Ring-billed. There is some precendence for the hybrid theory (see photos here of a Spanish bird suspected of this mix). It's important to emphasize that this pairing has never been verified in the wild - no courting or nesting evidence. As for melanistic Ring-billed Gull, melanism in gulls usually expresses itself unevenly and tends to be more blotchy. The Superior gull was "perfectly" pigmented like a fresh juvenile LBBG. The most likely explanation is a juvenile Ring-billed packed with a high dose of melanin. Observers: Robbye Johnson, Thomas Shultz and others. 
    2. A banded adult type Lesser Black-backed Gull was reported on the Mississippi River at Lock & Dam 3 in Goodhue County, Minnesota. The bird was sporting a black field-readable band on its right leg with 3 white characters. It also wore a metal band on its left leg. Unfortunately, the 3 characters on the black band can not be read clearly, but the combination matches none from North America. The only LBBG banding program using a similar field-readable is from the UK. Observer: Alex Franzen.
    3. Continuing the trend of increasing reports, putative Herring x Lesser Black-backeds were reported from several regions this month (Michigan, New York, several from New Foundland and Florida). All reports/photos represent adult birds.
    4. A very interesting adult gull with Taimyr/Mongolian-like attributes was photographed in Alameda County, California on 10 November 2016. The bird does not resemble any taxon or putative hybrid that regularly occurs in North America (photos here). Observer: Noah Arthur.

    November 2016 Quiz

    Age: Pointed primaries, patterned wing coverts and some apparent juvenile scapulars assist in aging this gull as a 1st cycle individual. Most of the lower scapulars are juvenile (=1st basic), but the faint gray upper scapulars are non-juvenile (=formative or 1st alternate).

    Identification: The uniform paleness to this bird suggests a large 4-year white-winger. Our white-wingers are Glaucous, Glaucous-winged, Thayer's and Iceland Gull. The mostly black bill pattern would be inconsistent with Glaucous Gull, especially one that has already renewed some scapulars. The primaries are too pale for a Thayer's Gull. This leaves us with Glaucous-winged and Iceland Gull.

    A few features should immediately jump out at the observer as pro Glaucous-winged: This is a bulgy gull with a short wing projection and a long/strong bill. Iceland Gulls tends to show more petite bills, longer wings, and proportionally larger eyes placed lower on the face.

    This month's quiz bird was identified as a 1st cycle Glaucous-winged Gull. This age group regularly shows variable scapular molt early in its hatch year. The molt can be absent to extensive. The bill pattern also varies from all-dark to paling around the base. Interestingly, some hatch year Glaucous-winged Gulls show this "mismatched" whitish head against a darker body. Whether this is due to bleaching, an early molt restricted to the head/neck, or just natural variation isn't clear.

    January. San Mateo County, California.

    24 November 2016

    Putative Chandeleur Gull, California and Thiceland Gull

    Michigan City, Indiana. 20 November 2016.

    Chandeleur Gull

    Sunday was my first genuine attempt at finding large gulls this season. Southern Lake Michigan's putative Kelp x Herring Gull (Chandeleur Gull) was holding to its regular post at Michigan City.

    Always a late prebasic molt, p-molt is only about 1/2 way completed. The mirror on p10 is still relatively small (as it has been for years) with a squarish shape.

    Mantle color tending toward Kelp, being a couple of shades paler than the primary tips. The head is blocky and the bill is hefty - similar to many Kelps.
    I've now committed this bird's distinct voice to memory and this is how I was alerted to its presence. The long call doesn't sound like Herring Gull at all. Back in 2014 I also found this bird via its long call. After listening to multiple Kelp recordings, I've concluded that the voice is about as close of a match as one could expect for a bird that presumably has mixed genes.

    The assumption here is that this individual associates with Herrings, and likely breeds (or attempts to breed) in Herring colonies. This also implies that it probably summers to our north (as opposed to our south), moving in with the first big waves of Herring Gulls that arrive on Lake Michigan in the Fall.

    The underside to the flight feathers is dark gray (not black), and the legs are variably greenish-gray with very faint hints of pink, particularly around the webbing of the feet.

    California Gull

    Moving on, a continuing adult California Gull also brightened up the day. It's believed this bird has been in the area since late August.

    The upperparts are darker than most CAGUs I've seen in these parts, but the bill is longer and "stronger" than average. I'm not sure how useful it is to try to assign these out-of-range birds to a specific subspecies. Interestingly, California Gulls banded as chicks in the Great Basin - presumably nominate californicus - have been recorded in the Lake Michigan region.

    Thiceland Gull

    No Lake Michigan day of gulling would be complete without a "tweener". At rest on the water the bird looked like it was going to be a Thayer's Gull:


    Take a look at it in flight...

    The wingtips looked paler than expected, and the markings were limited to the outer webs.

    Fine, we'll call it a Kumlien's or whatever suits your fancy...

    01 November 2016

    Monthly Notables October 2016

    • Glaucous Gull (2nd cycle type). Essex County, Ontario. 04 October 2016.
      • Continuing since at least July!
    • California Gull (2nd cycle). New Haven County, Connecticut. 04 October 2016.
    • Great Black-backed Gull (juvenile). Galveston County, Texas. 07 October 2016.
      • Only the second time this species has been recorded in Texas in October.
    • Chandeleur Gull (adult). Mobile County, Alabama. 08 October 2016.
      • Tending toward Kelp. Associating with Herrings on Pelican Island.
    • Chandeleur Gull (adult). LaPorte County, Indiana. 09 October 2016.
      • Reoccurring southern Lake Michigan hybrid.
    • Mew Gull (1st cycle). Nome County, Alaska. 09 October 2016.
      • Apparent Kamchatka Gull in Gambell.
    • Black-legged Kittiwake (2nd cycle type). Johnson County, Iowa. 10 October 2016.
    • Slaty-backed Gull (adult). Pierce County, Washington. 12 October 2016.
      • Continuing. This individual now a regular in the Gog Le-Hi-Te Wetlands area.
    • Iceland Gull (adult). Salt Lake County, Utah. 13 October 2016.
      • Kumlien's. First October record and earliest Fall arrival for Utah. Previous to this the earliest arrival was 04 November 2008.
    • Black-headed Gull (presumed adult type). Marion County, Kansas. 15 October 2016.
      • Photos of a red-billed bird were very promising but bird was not relocated.
    • California Gull (3rd cycle type). Rock Island County, Illinois. 18 October 2016. 
      • Recorded on the Mississippi River, moving between Illinois and Iowa.
    • Yellow-legged Gull (adult). St. John's County, Newfoundland. 21 October 2016.
      • The only location in all of North America where the species is expected.
    • Western Gull (2nd cycle). Morgan County, Colorado. 21 October 2016
      • Banded. Likely the same individual first found in Washington County in June. 
    • Little Gull (1st cycle). Oklahoma County, Oklahoma. 22 October 2016.
    • Black-legged Kittiwake (juvenile). Clark County, Nevada. 23 October 2016.
      • Less than 10 records for the entire state.
    • California Gull (adult). LaPorte County, Indiana. 24 October 2016.
      • In the area since late August.
    • Black-legged Kittiwake (juvenile). Ralls County, Missouri. 26 October 2016.
    • Little Gull (adult). Lake County, Indiana. 29 October 2016.
    • Black-legged Kittiwake (juvenile). Cook County, Illinois. 30 October 2016.

    Miscellaneous Notes
    1. Lesser Black-backed numbers begin to build in coastal Florida in October. On 17 October 2016, Michael Brothers observed F:003 in Volusia County, FL. This individual, banded on 20 March 2015 in the same county, is more evidence that Florida's growing LBBG population exhibits some winter site fidelity.
    2. Putative Chandeleur Gulls (Kelp x Herring hybrids) have not vanished from the earth. October has become the month that these hybrids are reported with more frequency, especially on the Gulf Coast. Two were recorded this month (Indiana and Alabama) with a third candidate in Texas (Galveston County; 12 Oct 2016). Note that roughly 30 hybrid types were found back on the islands in the breeding season of 2015. I do wonder why more pure Kelp Gulls are not being reported in the ABA area. Perhaps some are being overlooked as large Lesser Black-backs, or, most are programmed to "winter" south of the equator.

    31 October 2016

    October 2016 Quiz

    Age: The adult-like gray scapulars down the middle of the back and lightly marked uppertail coverts immediately suggest a 2nd cycle type. Also, the solid black tertials with relatively wide white edges support a bird not in its 1st plumage cycle.

    Identification: The largely uniform brown wings and dark gray central scapulars point to a dark-backed species. The checkered lesser and median coverts are suggestive of Lesser Black-backed Gull. The lightly barred/marbled region in the tail feathers (specifically the partition between the black tail band and white uppertail coverts) also resembles LBBG, and that's what this month's quiz bird was identified as.

    Berrien County, Michigan. September.

    Here's a more detailed photo of this rather "large" Lesser:

    10 October 2016

    Possible 1st Cycle Herring x Lesser Black-backed Gull

    I'll begin this post by reiterating - as I always do - that I'd much rather leave confusing young gulls unidentified than assign a hybrid label to them. There is no sense in jumping to conclusions when there are no data to support them.

    With that said, here's a bird I first thought may be a 1st cycle Lesser, then decided it was okay for a 1st cycle Herring, and then started scratching my head the longer I looked at it.

    Structurally, the rear looks very little like an American Herring and much more like a Lesser. The sparsely marked vent area is also unusual.  
    The, longer, solid outer median and lesser coverts also resemble Lesser Black-backed, more than American Herring.
    "This is NOT a pure American Herring" were my thoughts after seeing the undertail.
    The white vent is not something I've encountered with juvenile American Herrings. But now see the open wing...
    The uppertail contrasts greatly with the rest of the body, but most disturbing is the strong contrast to the pale inner primaries (only seen well in brighter lighting).
    In this slightly underexposed image, it looks long-winged, shows less of an inner primary window, and the tail almost looks like it was trying to go for a banded look but failed miserably. 
    If this is an American Herring Gull or Lesser Black-backed Gull, then I have to admit that I don't yet know these species well. It sure doesn't feel right for either taxon. On the other hand, it does look intermediate in many ways. Another one for the mystery file.

    Juvenile Lesser - Little Pretty

    I'm up to my 5th juvenile LBBG so far this season. This one really hit the mark with stunning outer tail feathers showing spectacular barring:

    New Buffalo, Michigan. 07 October 2016.

    The breast often looks more coarsely marked than American Herring.

    Head/neck streaking finer and less marked than in American Herring counterparts. The undertail is with a white base and a neater pattern. The vent area has significantly less markings than American Herring.

    Comparisons, now, with an American Herring Gull:

    09 October 2016

    Michigan City & New Buffalo - 07 October 2016

    Just a few miscellaneous notes on birds seen on Friday.

    Herring with virtually no mirror on p10 (still growing). P4 with small speck on outer web and marked p-coverts/alula suggest a 4th cycle type. Michigan City, IN. 07 October 2016.

    Same individual above. A mostly adult-like bird near finishing prebasic molt.
    Another adult type with a large p10 mirror showing several white "spots" on the underside of the primary. P-9 with a weak thayeri pattern. Michigan City, IN. 07 October 2016.
    Adult type Herrings. Left bird already in nonbreeding condition while the bird on the right has bright legs and bill. The most natural explanation for this is hormonal variance. 
    Sub-adult Herring with the often-seen black ink spot on the tertials. Also of interest on this bird is subtle hints of wavy barring on the neck/breast. Although this is most commonly seen on Glaucous-winged Gull, Herrings too can show it.
    1st cycle Herring with ~90% of scapulars 2nd generation. Rare is to see a few (inner) upperwing coverts replaced already (likely PA1). Bill is beginning to pale. Also of interest on this bird is a paling forehead, an attribute often found in similar-aged California Gulls.
    2nd cycle Herring Gull. A very obvious marbling to the greater coverts and tertials, unlike in 1st cycle birds. The primary tips are rounded (and still growing - see next image).

    A still largely marked tailband, with reduced markings on the upper rump. The inner primaries are more silvery than is seen on 1st generation primaries. The axillaries are mostly white as expected at this age.
    1st cycle with ~100% of scapulars replaced. Somewhat unusual is a few wing coverts (median and greater) have been renewed. This usually doesn't take place with the majority of hatch year herrings that I encounter. A better angle of this in the photo below..

    6th Cycle American Herring Gull

    A short visit to New Buffalo on Friday, 07 October 2016, yielded this cooperative adult that allowed a full band read:

    #1106-19489. Banded as a flightless chick in Egg Harbor, Wisconsin on 15 June 2011.

    The bill is relatively small for Herring, suggesting a female type. 

    Although the black w-band on p-5 (right wing) is typical, the white tongue tip is not.
    Primaries out to p7 fully grown.

    P8 almost fully grown, p9 about 1/3 grown and p10 just coming out beyond the wrist.
    Outermost and innermost secondaries growing. Most secondaries still tucked under greater coverts.

    There was a 2nd banded HERG too but a hopeless chance of capturing the entire sequence:

    Dirty band in need of replacement. The condition of this band doesn't neccessarily imply the bird is old. It could just be this individual has been exposed to lots of "sticky" stuff.

    08 October 2016

    Nelson's Gull - A Muddy Hybrid?

    Nelson's Gull. What is a Nelson's Gull and where do they originate from?

    The name Nelson's Gull is commonly used for Glaucous x Herring hybrids found on the North American continent. It's generally assumed - by most - that the Herrings involved are American Herring Gulls (smithsonianus).

    In this post I review the historic nomenclature surrounding this hybrid and also shed light on the implications that come with the current usage of the name "Nelson's Gull". In short, our usage of this label is a deviation from the literature.

    Putative Glaucous x Herring hybrid (right) with American Herring Gull.
    Chicago, Illinois. 08 February 2015.

    The Beginning - Nelson's Gull as a Species

    The first known specimens of this taxon were collected by E.W. Nelson in Alaska. The type specimen is housed at the U.S. Natural History Museum. #97253. Adult male. Collected at St. Michaels, Alaska. 20 June 1880.

    H.W. Henshaw later reviewed the skins and was confident that E.W. Nelson had discovered a new species, describing it as the Pacific counterpart to Kumlien's Gull, only larger and with a darker primary pattern (Henshaw also treated Kumlien's as a "good" species).

    It was Henshaw who designated the name Nelson's Gull (Henshaw 1884).

    From Species to Hybrid

    Jonathan Dwight was among the first to suspect nelsoni may be a hybrid form, noting that it showed intermediate characteristics between Glaucous and Herring Gull. The fact that "no two of them are marked alike" was Dwight's primary concern. He also pointed out that very few specimens are available and no known breeding colonies existed, inferring Nelson's must be an intermediate form that sporadically occurs as a result of hybridization. Incidentally, in his monograph, Dwight also casts doubt on Kumlien's Gull being a valid species (Dwight 1925).

    Dwight's assessment of the nelsoni collection available in his time included the following: "Larus nelsoni are chiefly in the plumage of hyperboreus with touches of grayish or dusky pattern on the outer primaries that might well be derived from the black of L. aregentatus vegae."

    He goes on to say, "...but the pattern of the primaries is just what would be expected if the black color of Larus argentatus vegae were diluted, withdrawn or diminished in varying degree".

    The lord of gull ornithology declared this taxon a hybrid.

    Plates of nelsoni primary patterns found in
    Jonathan Dwight's "The Gulls of The World". Figure 211 & 212.

    Which Herring Parent?

    Admittedly, the description of the primary pattern(s) is not extensive or in-depth, but there can be no doubt that Dwight regarded the Herrings involved, Vega Herrings - not what we today understand as American Herrings (smithsonianus).

    After being reduced to a hybrid form, the historical timeline becomes obscured and somewhere along the line Nelson's Gull became the label for hyberboreus x smithsonianus. Vega influence was seemingly supplanted and locked away in museum drawers.

    To be clear, our common usage of the label "Nelson's Gull" is 50% flawed.

    The Plot Thickens

    The fundamental problem - like with many of our presumed 4-year hybrids - is that data from birds of known origin are scant. The Glaucous x Herring hybrids found to the south in the winter season (i.e., in the lower 48 states and eastern Canada) may very well be hyperboreus x smithsonianus, but this certainly can't be the case in Alaska and throughout the Bering Sea, at least not exclusively!

    One specific case in point is the mixed Glaucous x Herring pair that was discovered breeding in Bluff, Alaska in 1977. The pair successfully fledged young and Drury confidently identifies the adult Herring as a Vega Gull (Patten 1980).

    Bluff - also known as Apookauchuk on some maps - is roughly 60 miles to the southeast of Nome and is a rock's throw from St. Michaels (the region where Nelson collected his specimens).

    The situation is equally confounding throughout the Seward Peninsula in the summer months where both taxa (vega and smithsonianus) can be found as nonbreeders (Kessel 1989).

    Howell and Dunn are quite cautious in their guide and seem to avoid the use of "Nelson's Gull". Consider the presumed hybrid in plate H3.13 in Howell & Dunn. The identification of such a phenotype - in Nome - is anyone's guess and the authors readily point this out. But in the same section the authors give many other examples which are identified as having "American Herring Gull" parentage. It would seem that they're identifying these hybrid types based on range, and they're probably correct.

    Larry Spear - "Larophile and Scientist Extraordinaire"

    In 1984, the late Larry Spear (to whom Howell & Dunn dedicated their gull guide) discovered interbreeding among Glaucous and Herring Gulls in the far north near the Mackenzie Delta in Canada. In his report Spear provides a hybrid index used to score some 50 intermediate birds (Spear 1984).

    Oddly, he never once elucidates whether the Herrings involved were vegae or smithsonianus. But he does reference Macpherson and Smith when describing the wingtip pattern of a pure Herring Gull. This leads me to believe he presumed the Herrings were smithsonianus (in accordance with the AOU's line of reasoning, L. argentatus smithsonianus). Further, smithsonianus is the expected taxon in Arctic Canada.

    You can find more of Spear's photos in "Gulls of the Americas" (plate 1.6 and plate H3.3).

    Interestingly, Larry Spear was under the impression that he had documented the "first" known interbreeding among Glaucous and Herring Gulls in North America (the 1977 record from Bluff, Alaska was either unpublished at the time, or was completely missed by Spear). It could be that Spear implied he found the first Glaucous x "American" Herring hybrids. Nevertheless, Larry Spear was the first to document multiple hybrids, together, with young. With that said, he never uses "Nelson's Gull" as a label for these pairings.

    The only other concerted effort made to analyze Glaucous x Herring hybrids in the last 30 years was by Agnar Ingolfsson. Ingolfsson examined a multitude of specimens from arctic North America and found that roughly 25% of the hyperboreus skins that came from Alaska appeared to be hybrids between Glaucous and Herring Gull. Compare that to only 1% of the skins that he examined from Canada (Strang 1977). This, in my humble opinion, warrants serious reconsideration of what we call Nelson's Gulls.

    Moving Forward

    North American gull enthusiasts and field ornithologists largely agree that splitting Vega (vegae), American (smithsonianus) and European Herring (argentatus) has been long overdue. The AOU is patiently awaiting substantive research and evidence before acting on these taxa, and this is commendable. There is nothing simple when it comes to Herring Gull identification, and at times, separating 1st cycle birds is bewildering.

    With respect to hybrids, questions such as "Which Glaucous subspecies is involved" and "Which Herring taxon is involved" may never be clearly answered with non-nesting birds, but I would argue that any suspected or known Glaucous x Vega hybrid should be given a unique label that differs from what we would call a Glaucous x American Herring - If only to emphasize Vega's distinctiveness (similar to Glaucous x European Herring hybrids in Iceland which are commonly referred to as Viking Gulls).

    Although this may seem like hair-splitting for some, I've chosen to discontinue the use of Nelson's Gull to describe putative Glaucous (hyperboreus) x American Herring (smithsonianus) hybrids. For hyperboreus x smithsoninaus, I think Spear's Gull, Mackinzie Gull or Hudsonian Gull would be welcome (more on this later).

    It will be somewhat inconvenient to adjust the current usage of "Nelson's Gull", but I think it can be salvaged and restored to what was originally intended by Dwight. Putative hyperboreus x vegae should rightfully be referred to as Nelson's Gull.


    Dwight, J. 1925. "The Gulls (laridae) of the World: Their Plumages, Moults, Variations, Relationships, and Distribution." Bulleting of the AMNH 52:63-402.

    Henshaw, H.W. 1884. "On a New Gull from Alaska." Auk 1:250-52.

    Howell, S.N.G. and J.L. Dunn. 2007. A Reference Guide to Gulls of the Americas. Peterson Reference Guide Series. Boston: Houghton Mifflin.

    Kessel, B. 1989. Birds of the Seward Peninsula, Alaska. Fairbanks: University of Alaska Press.

    Patten, S.M. 1980. "Interbreeding and Evolution in the Larus glaucescens, Larus argentatus Complex in the South Coast of Alaska." University of Maryland, Ph.D. thesis.

    Spear, L.B. 1987. "Hybridization of Glaucous and Herring Gulls at the Mackenzie Delta, Canada." Auk 104:123-25.

    Strang. C.A. 1977. "Variation and Distribution of Glaucous Gulls in Western Alaska." Condor 79:170-75,