North American Birds

VOLUME 69 NO2 2016

A Quarterly Journal of Ornithological Record Published by the American Birding Association. The mission of the journal is to provide a complete overview of the changing panorama of our continent’s birdlife.

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T H E C H A N G I N G S E A S O N S : C A R B O N C O P Y V O L U M E 6 9 ( 2 0 1 6 ) • N U M B E R 2 203 found food too scarce in areas south of Pa- cific Grove. As for Varied Thrushes, acorns make up a significant portion of Band-tailed Pigeons' diet, and one suspects that the in - cursion of unusually high numbers in places not usually recorded, particularly towns in southern California and the floor of the Cen- tral Valley but also across much of northern California (Figure 7), suggest inadequate resources farther north and upslope. Migra- tion of the species from the northern parts of range is annual and expected; in California, presumably most or all birds are of the Pa- cific coastal subspecies, monilis, rather than the nominate, which is found mostly in the Rocky Mountains, though some individuals apparently do move between these popula- tions (Keppie and Braun 2000). Acorns, the fruits of oak trees, are them- selves fascinating and unpredictable in their abundance. In some autumn seasons, the acorn crop will be massive, with mul- but stuck around all winter: eBird graphs of frequency (percentage of checklists record- ing a species) in January/February of 2014 show about 2% of checklists with Varied Thrush, while the same months in 2015 show 14% or more! One has to wonder, dur- ing these infrequent super-flights, whether large number of nominate naevia aren't also involved. While watching the Varied Thrushes, Sullivan also observed thousands of Band- tailed Pigeons in passage (Figure 6), also well above the usual numbers seen in migra- tion here, 17 November. These birds were part of a major movement of the species, perhaps indicative of an excellent breed- ing season, perhaps indicative of a crash in food resources (or both); see the S. A. Box in the Northern California report for more details. Interestingly, the birds at Point Pi- nos were moving northward, which perhaps indicates reverse migration, if the birds had ins (Figure 5). The previous high count for the county was in 1972, on the Monterey Peninsula Christmas Bird Count, some 348 birds found by 48 people in 162 hours of birding. Roberson (pers. comm.) notes that 750 is certainly a new record but that "major flights of Varied Thrush in the same magni- tude of the fall 2014 incursion have almost surely occurred [in this area] before, and probably did so in both 1972 and 1996, at a minimum." Roberson and colleagues saw more than 100 passing over Pacific Grove in just 15 minutes on 27 October 1996 (see Roberson 2002). And 90 years earlier, far- ther north, ornithologist Joseph Mailliard observed "thousands" of Varied Thrushes in migration over coastal Marin County, California, with "hundreds in sight at once in any direction one might look," between dawn and 10:00 a.m. on 20 October 1906 (Bent 1949). The Varied Thrushes involved in the 2014 flight didn't just pass through Figure 8. This adult male Western Tanager appeared for only a day at Spanish Fort in Baldwin County, Alabama, 3 February 2015. In the twenty-first century, the species has become an almost-expected backyard visitor in the Southeast, along with orioles and hummingbirds. At least one Western Tanager has wintered in Oregon/Washington annually since 1998! Photograph by Cathy Gray.

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