Grinnell & Miller's (1944) The Distribution of the Birds of California is the California birder's bible for details of past status and distribution. The classic work is the underpinning of all current distributional projects. The details published about ranges and dates are almost always backed up by specimens, and thus are widely accepted as "true." In most cases those details are, in fact, true.
But there can be exceptions. Recently, due to some posts on the "Monterey Bay Birds" chat line and because (coincidentally) I was working on rewriting the gulls section for Monterey Birds, 2d ed., the topic of summer records of Glaucous Gull Larus hyperboreus around Monterey Bay came up. The problem with summer claims of Glaucous Gull is that very worn first-year gulls of other species, often Glaucous-winged Gulls but sometimes even a worn California Gull (like the bird shown at right, photo'd at Roberts Lake, Seaside, on 18 July 1980) can become so bleached as to appear white, and can superficially have two-tone bills recalling Glaucous Gulls. Those believing that there were some acceptable summer records of Glaucous Gulls pointed to a specimen cited by Grinnell & Miller (1994) from Santa Cruz, taken on 14 June 1938 and said to be #87919 at the Museum of Vertebrate Zoology, U.S. Berkeley. In an MBB post in January, I wrote that "I suspect the specimen may be misidentified" and thus might not support other June-July-August claims of Glaucous Gull.
It is true that some late first-year Glaucous Gulls linger into May -- maybe even to late May -- but beyond the specimen I was unaware of any conclusive evidence of mid-summer Glaucous Gulls in central California. There is a photo-documented bird from Monterey Bay on 2 Sep 1985 which appears to be a Glaucous Gull and looks quite worn, strongly suggesting that it over-summered someplace nearby. Summer birds thus are theoretically possible, but how often and with what level of documentation was at issue.
On 17 Feb 2000, I visited MVZ and tried to locate the specimen. First off, it wasn't in the Glaucous Gull drawers. So I asked the collections manager, Dr. Carla Cicero, to help me search it out. She pointed out something that I didn't know: the entire data-base for the MVZ collection is now on-line at http://elib.cs.berkeley.edu/mvz/.We punched in the specimen number ("87919") and got this response:
It seemed very odd that the both the i.d. and the date should be wrong, so Dr. Cicero searched out the ORIGINAL accession card to the museum. This was hand-written back when the specimen was given to the museum in 1941 by Mr. Streator. That accession cared showed the i.d. as Larus hyperboreus, the Glaucous Gull, and the date was unmistakably 14 June, not January. So what was published by Grinnell & Miller matches the original i.d. and date. So the mystery deepened....
Dr. Cicero and I then went searching for the specimen and eventually found it, resting among the Glaucous-winged Gulls. the photo above is of specimen #87919. The wings and tail were very badly worn and bleached white, with primary shafts protruding -- I knew before we looked at the label it was a June bird.
In this hand-held shot (right; unfortunately "overflashed") you can still get the feeling of the extremely worn wingtips. And indeed the label confirmed the date: it was 14 June 1938 after all. [This means the data entry was wrong in the data-base; one can expect typographical errors any time large amounts of data are transferred. Dr. Cicero will also undertake to correct the database after our adventure.]
The bird is unquestionably a Glaucous-winged Gull, showing some pale to the base of the bill as is typical of first-summer Glaucous-wings but not nearly the bicolored sharpy-demarcated bill of first-year Glaucous Gulls. The history of the re-identification appears on the label in pencil. Streator had stated it was hyperboreus (Glaucous Gull) but his mistake had been previously noticed and the specimen reidentified sometime later by "D.J." who also wrote in pencil that the bird was glaucescens and in "2nd year" plumage. This mistake in ageing was later corrected, in pencil, to "first year" by "S.F.B." whom I know to be Stephen F. Bailey.
Mistakes in identification do occur among museum specimens. Just because a bird was collected doesn't mean the collector and/or preparator could identify it. But specimens are very useful because they can continue to be reviewed indefinitely [likewise, photos or written details placed in public institutions where they can be accessed can always to re-reviewed years later]. In fact, another mistakenly-identified specimen that I found at MVZ led to a publication that removed an entire species from the North American list! [see Roberson & Pitelka 1983].
So the mystery of the "June specimen of Glaucous Gull" in Santa Cruz is solved. It was a worn first-year Glaucous-winged Gull, and thus there are no photo or specimen-backed records of Glaucous Gull anywhere on Monterey Bay in June, July, or August. Indeed, after reviewing the database of late spring/summer records in the North American Birds notebooks (thank you, Steve Rottenborn), it appears a thorough review of all California summer claims of this species may be warranted. In undertaking such a review, here are some words of wisdom from Curtis Marantz (1986) in citing nine accepted late fall and winter records in San Luis Obispo County (just to the south of Monterey Co.): "Many of the record of [Glaucous Gull] probably pertain to misidentified Glaucous-winged Gulls, thus numerous records with unsatisfactory documentation have been rejected." I have taken this point to heart, and therefore currently find no Monterey County records of Glaucous Gull between 4 May and 2 September. Yet -- as the 2 September bird shows -- it apparently can happen. But when it does, the record needs thorough documentation.
Key lessons to be learned from this small mystery:
Marantz, C. 1986. The birds of San Luis Obispo County, California: their status and distribution. Senior thesis, Biol. Sci. Dept., School of Science and Mathematics, Calif. Poly. State Univ., San Luis Obispo.
Roberson, D., and F. A. Pitelka. 1983. Occurrence of Willow Warbler (Phylloscopus trochilus) in North America refuted. Condor 85: 258.
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