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the pattern of the primaries is just what would be expected if the black color of Larus argentatus vegae were diluted, withdrawn or diminished in varying degree".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

References

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,