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There are two geographically separated breeding populations of Bell's Vireo: a large eastern population that breeds from southeastern California eastward, and a small southwestern population that breeds in southwestern California and northwestern Baja California (see range map). The southwestern population is composed of one subspecies, the Least Bell's Vireo (Vireo bellii pusillus). The Least Bell's Vireo is grayish above and whitish below with faint pale "spectacles" around the eyes and pale wingbars (pictured). The Least Bell's Vireo requires riparian habitat for breeding and was formerly abundant in riparian woodlands of southwestern California and northwestern Baja. It was reduced to just 300 pairs by 1986 due to loss of riparian habitat and brood parasitism by the Brown-headed Cowbird, thus was listed as an endangered species by the state and federal government. Critical habitat was designated from Santa Barbara to San Diego County, which spurred removal of exotic plants and trapping of cowbirds; by 2004 the vireo population increased to 2,500. Least Bell's Vireos breed at Four Seasons and likely were established only after the habitat restoration in 2006 (see Len Tavernetti's articles in the March 2018 and September 2019 issues of the Breeze). Thus, everyone who lives in the Four Seasons Beaumont community has helped the recovery of the Least Bell's Vireo by choosing to live in one of the few retirement communities that has a conservation easement which, according to the Birding Club's 2019 count, created breeding habitat for five pairs of Least Bell's Vireos. ~ Steve Edelman Birding CLUB This month's Club communication is devoted entirely to our very own endangered species, the Least Bell's Vireo, and summarizes the results of a survey we conducted this past summer. Each survey followed the same route covering all of Trails A and B, resulting in two duplicate counts of 4,900 linear feet of our riparian habitat. We conducted a total of 42 surveys between March 4 and Sept. 26, 2019 and plotted the counts (see graph). The survey found that the first vireo arrived on March 24 ± 1 day; during late March through early May, the number increased to a high of 7; 5 mated pairs succeeded in breeding through the end of July; and numbers dwindled for a month and half after that until the final bird departed on Sept. 17 ± 2 days. Thus, each mated pair territory occupied about 1,000 linear feet of streamside riparian habitat. Email steve.h.edelman@gmail. com for a pdf copy of our full report. ~ Steve Edelman FOUR SEASONS BREEZE | NOVEMBER 2019 37 Bird of the Month Least Bell's Vireo (photo by U.S. Fish & Wildlife Service) The gray line is the actual vireo count and the heavy blue dashed line is an interpreted total number present The breeding/summer range of the Least Bell's Vireo is southwestern California and northwestern Baja California

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