Runtism Revisted

Near my home in Everett, Washington, the Public Boat Launch is a great place to look at gulls, even if it never seems to host rarities. On November 15th this year, I was surprised to pull in and find this rather rust-buffy gull wandering around among the California and Ring-billed Gulls.  It was obviously smaller than any of the ~100 California Gulls nearby. That and its bright coloration grabbed my attention.

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This very small first-cycle California Gull was photographed at Everett, Snohomish County, Washington on 15 November 2009. When compared directly with other California Gulls, like the three second-cycle birds in the image below, it looked distinctly smaller.

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On closer inspection, it became apparent that this bird had plumage characters typical of a first-cycle California Gull, excepting perhaps, its rather rusty coloration. The worn buffy feathers on back, head, belly, and wing were retained from juvenile plumage. The crisp gray scapulars (with their internal anchor-like markings) and the scattered gray feathers on the underparts represented newly acquired first-winter plumage. Additionally, the bill was in between the solid dark of a juvenile and the black-tipped pink bill of a first-winter California Gull.

In my experience, nearly all hatch-year California Gulls in Washington have already transformed from juvenile to first-winter plumage by November. However, Gulls of the Americas by Howell and Dunn states that some California Gulls retain juvenile plumage into December. Some fresh juvenile California gulls are a beautiful peachy-buff during July and August. Wear to such a plumage could easily explain the rusty-buff appearance of this bird. The size, however, was still a puzzle.

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As shown in the images above and below, this California Gull not only looked much smaller than the other California Gulls present, but it also appeared to be smaller than many of the Ring-billed Gulls.

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The National Geographic Field Guide to Birds of North America and the Sibley Field Guide to Birds of North America both list the length of California and Ring-billed Gull as 21 and 17.5 inches, respectively. Interestingly, Gulls of the Americas gives a size range of 18 to 23 inches for California Gull and 17.3 to 20.5 inches for Ring-billed Gull. That book, however, then uses "smaller" as the first character for separating Ring-billed Gull from California Gull. In any case, prior to seeing this bird, I do not think that I've seen a California Gull that was clearly smaller than the Ring-billed Gulls it was with. 

So, what is my point here? It is that "runts" really do occur. The July 2009 chapter of BirdFellow contains a piece I wrote entitled The Midget Frigate: Confusion in the Baja Sun. In that piece, I presented photographs of a Magnificent Frigatebird that appeared to be smaller than the "normal" range for that species. Some well-known birders I'd discussed this with had questioned whether or not "runt" birds really existed. Perhaps prescient was Tony Leukering who said that if any species occasionally displayed "runtism," it was California Gull. This bird in Everett seems to be a fine example.

CAGU-09Nov-Everett10a

Here the subject gull looks noticeably smaller when in the company of an adult Ring-billed Gull (back left) and a second-cycle California Gull (right)

Interestingly, in response to the "Midget Frigate" piece, Chris Hill of Coastal Carolina University pointed out an article by Hicks (1934) in Bird-Banding which studied variation among 10,000 Eurasian Starlings that were captured and measured. Six of these were considered "pigmy," being at least 10% shorter than the average (not including any tail abnormalities). A ten percent difference in length would probably translate into a fairly detectable difference in overall size.

Thus, it seems from Magnificent Frigatebird to California Gull to Eurasian Starling, runt birds do exist. Beyond being a point of curiosity, this would also suggest that we exercise caution when using size to determine identification.

All photos taken by Steve Mlodinow. 

1

This is great stuff, Steve; thank you. I have a “runt” House Finch at my feeder here in Tucson right now. It’s a female-plumaged bird, apparently normal in all aspects but size. The bird is a good half inch less in length than its companions, a significant difference in a small passerine.

2

Hi Rick
Egads, such a small House Finch might lead one to even think Pine Siskin upon a quick glance! Most interesting.

3

Great timing with the article! Just yesterday, while on the shores of Lake Erie, I encountered a Ring-billed Gull displaying all the same charactersitics of your California. This bird still had quite an obvious amount of retained rusty juvenile coloration, intermediate bill, and was quite noticeably smaller than the other ringers. When it began flying around, it became apparent that it was experiencing heavy wing molt, something Ring-billeds should have completed months ago. Pretty cool stuff!

I encountered an adult Ringer last season that was MUCH smaller (~25%) than others.

Good birding!

4

Apple now has Rhapsody as an app, which is a great start, but it is currently hampered by the inability to store locally on your iPod, and has a dismal 64kbps bit rate. If this changes, then it will somewhat negate this advantage for the Zune, but the 10 songs per month will still be a big plus in Zune Pass’ favor.

5

Wow I must confess you make some very trechnant points.

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