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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N O R T H A M E R I C A N B I R D S 290 N O R T H E R N C A L I F O R N I A there of 50-60 on 1 Jan (George Folsom). Mendocino's first Common Ground-Dove visited the Ukiah W.T.P. 14 Dec (SJS, †Rich Howard, DAJ, ph. DAB). Three White-winged Doves included singles at Pescadero, San Ma - teo 23 Nov+ (GrH. ADeM, ph. DMo), s. Ar- cata Bottoms, Humboldt 18 Dec–5 Jan (Annie Meyer, m.ob.), and Crowley Lake, Mono 20 Dec+ (Steve Brad, m.ob.). Establishing the fourth record for Stanislaus, a Northern Saw- whet Owl called repeatedly from Grayson Rd. 4 Jan (†HMR, John Vixie). Vaux's Swifts are scarce in winter; the only birds reported were one at Felt Lake 15 Dec during the Palo Alto C.B.C. (the third in winter for Santa Clara; PDu) and 2 at H.R.S. 27 Feb (RJR). The invasion of Lewis's Woodpeckers into portions of the Coast Range and C.V. that began in fall continued through winter. Santa Clara recorded its highest number of winter sightings away from areas of residency (110) since care - ful recordkeeping began in 1993, with a nearly 70% increase over the previous high count of 65 during the winter of 2003-2004 (WGB); 3 found during the Benicia C.B.C., Solano 15 Dec (Karen Sheldon, Sandi Hewitt) were the first documented on that count since 1978. Follow - ing the fall irruption of Acorn Woodpeckers, S.F. had its first occurrence of multiple winter - ing birds in many years, with a high count of 54 tallied on the S.F. C.B.C. 30 Dec (m.ob.). Sonoma's second Williamson's Sapsucker, a fe - male, was at Santa Rosa 29 Jan–4 Feb (SMcA, m.ob.). Although the species may prove to be resident in the remote ne. portion of Trinity, a bird in that area at Scott Mountain Sum - mit Campground 7 Dec (FrT) established the first winter record for the county. A total of 23 Yellow-bellied Sapsuckers was average and in - cluded Shasta's second about 2 km se. of McAr- thur 21 Dec–21 Jan (JLD, DRs, SRs, m.ob.). Numbers of Red-naped Sapsuckers appear to be increasing in the Region away from areas of residency. This winter's total of 31 established a new high count and was more than twice the long-term seasonal average. An imm. Crested Caracara near Harkins Slough 6 Jan (ph. Jon Ford) established the third record for Santa Cruz. The same bird was thought possibly to have been responsible for reports in Monterey in fall and then in San Mateo at Half Moon Bay 10-28 Feb (ph. Andrew Rush, ph. PJM, m.ob.). Seven Empidonax flycatchers were report- ed. They included 2 Hammond's, one each in Yolo and Sacramento; one Least, along the Salt River, Humboldt 4 Jan (†GSL), a first for the Centerville to King Salmon C.B.C.; and 4 Western (presumably Pacific-slope)—2 in Butte, one in Sacramento, and one in Santa Cruz. An Eastern Phoebe that spent its fourth consecutive winter along Stage Rd., San Ma - SA From fall through winter and continuing into early spring, the Region saw concurrent low- land irruptions of Band-tailed Pigeon, Lewis's Woodpecker, Steller's Jay, and Varied Thrush that were unprecedented based on available historical data. This phenomenon is well illustrated by data from the C.V., where Band-tailed Pigeons and Steller's Jays are generally absent and the relative abundance of Lewis's Woodpeckers and Varied Thrushes can vary dramatically from win - ter to winter. Figure 1 uses eBird data from C.V. counties whose boundaries are largely restricted to the valley floor (Kings, Merced, Sacramento, San Joaquin, Solano, Stanislaus, Sutter, and Yolo) to compare frequency of inclusion in eBird checklists from the fall 2014–spring 2015 period to the average frequency for the previous 14 years. In each case, the data show a pattern of most frequent reports in late fall and early winter, with each species continuing to be reported at a frequency far exceeding the historical average well into early spring. Data from C.V. Christmas Bird Count circles since 1978 allow us to put the magnitude of these irruptions into historical context. Band-tailed Pigeons were present this winter at an abundance (based on birds/party hour) five times higher than the long-term average and at the second high - est level from this period. Lewis's Woodpecker abundance set a new record and was nearly three times the long-term average. Steller's Jays were recorded at a level six times the average and twice the previous high. Varied Thrush abundance also set a new high and was eight times the long-term average. The irruptions of Band-tailed Pigeons and Varied Thrushes were particularly widespread, with the pigeons present in remarkable abundance in coastal Southern California and Varied Thrushes in unprecedented numbers throughout most the state. The causes of this year's phenomenon are unknown, but it is worth noting that all four of these species rely to some extent on acorns for food in fall and winter. According to Walt Koenig (http:// www.nbb.cornell.edu/wkoenig/wicker/CalAcornSurvey.html), 2014 was among the poorest years for acorn production in California, so perhaps low acorn availability was at least partially re - sponsible for the irruptions of some or all of these species. However, some oak species produced good or near-average acorn crops in some areas (e.g., valley oaks and blue oaks in the C.V. and Sierra foothills), and many or most of these birds (especially in the case of Varied Thrush) likely originated outside California. Furthermore, review of C.B.C. data since 1978 indicates that irrup - tions by these species are not necessarily synchronous, so that factors other than acorn produc- tion likely drive these species' irruptions. 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 % of eBird checklists with species Band-tailed Pigeon BTPI historical BTPI 2014-15 Aug Sep Oct Nov Dec Jan Feb Mar Apr May 0 2 4 6 8 10 12 14 16 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 % of eBird checklist with species Lewis's Woodpecker LEWO historical LEWO 2014-15 Aug Sep Oct Nov Dec Jan Feb Mar Apr May 0 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 % of eBird checklists with species Steller's Jay STJA historical STJA 2014-15 Aug Sep Oct Nov Dec Jan Feb Mar Apr May 0 5 10 15 20 25 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 % of eBird checklists with species Varied Thrush VATH historical VATH 2014-15 Aug Sep Oct Nov Dec Jan Feb Mar Apr May Figure 1. eBird data from Central Valley counties comparing the percent of checklists reporting each species from fall 2014 through spring 2015 to prior years (2000-2013).

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