December 1999 Mystery Birds

These two turned out to be exceptionally difficult. The jay is an Island Scrub-Jay (Aphelocoma insularis) which was recently split from the widespread Western Scrub-Jay (Aphelocoma californica). It was photographed 24 September 1996 on Santa Cruz Island where it is endemic. The wren is a Marsh Wren (Cistothorus palustris) photographed at Palo Alto Baylands, Santa Clara County, 30 January 1987.

I'm not surprised that few people wanted to tackle the jay. It's clearly either an Island or Western scrub-jay and the two are easiest to identify by range. In general the Island Scrub-Jay averages considerably larger and darker than its mainland cousin. There is more sexual dimorphism in the island jay with males having much heavier bills than females. Also the Island Scrub-Jay usually shows more blue on the undertail coverts and has proportionally heavier legs and feet. Nevertheless, these differences may be subtle, and depend on light conditions, film, or the monitor you may be using, etc. Overall size is impossible to judge in the photo and the undertail coverts are not visible. The bill size does not seem to me to be outrageously large, so I don't think it is a male Island Scrub-Jay, but it might be a female.

Are there any other, less ambiguous characters we can use? In going through photos from my teaching collection, I noticed that all photos of Island Scrub-Jay showed a black forehead and black nasal tufts. Those on Western Scrub-Jay show those areas much paler. I'm not sure if this is 100% reliable. My purpose of posting this image was to get feedback on the subject. Has anybody seen a Western Scrub-Jay with the forehead and nasal tufts as black as this bird? Interestingly this difference is illustrated in the plate on page 315 of the National Geographic Guide 3rd edition but is not discussed in the text. Incidentally, the plate in the National Geographic Guide incorrectly suggests that the breast band is solid on the Island Scrub-Jay and broken on the Western Scrub-Jay. In fact, there is no such difference.

Inclusion of the wren was prompted by a particularly contentious report of a Sedge Wren this Fall in the San Francisco Bay Area. The bird could not be relocated, but several Marsh Wrens were seen in the area, some of which showed faint streaking on the crown. The standard Field Guides suggest that a streaked crown is diagnostic for Sedge Wren but this photo demonstrates that is not necessarily true. Also some Sedge Wrens have the crown streaking quite faint. E.g. cf. the accepted record from Sycamore Canyon, VEN. I agree with those suggesting that a Sedge Wren would probably be much more contrasting buff in color, especially on the sides of the breast. The more prominent white eye-arc may also be a good indicator of Marsh vs. Sedge.

There is a good deal of geographic variation in Marsh Wren and some prior claims of Sedge Wren in California have been questioned in part, because of this variation. In commentary, Phil Unitt suggested that the mystery bird better fit the subspecies plesius or pulverius, breeding in the Great Basin/Rocky Mt. region which is even paler on the underparts than the race paludicola resident along the California Coast. I believe that people familiar with the resident subspecies may be confused by somewhat different looking migrants and winter visitors. In any event, extreme caution is advised when claiming a Sedge Wren anywhere in California.

I'd like to thank everybody for their courage in tackling these very difficult photographs. The original photos are below. To view public comments or join the fray by adding your opinion, click here. Have fun!

Photos © Peter LaTourrette. All rights reserved.

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