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Date: 3/10/25 7:09 am From: Daniel Edelstein via groups.io <danieledelstein...> Subject: [northbaybirds] Common Non-breeding Resident — VARIED THRUSH — Migratory Invasion Last Few Days In Pacheco Valle, Novato, Marin Co.
Per typical movement this time of year for northbound VARIED THRUSH in our region, I noticed visual and vocalizations for this species for the first time this "winter"/non-breeding season in our Marin Open Space District forest that borders our residence in Pacheco Valle, Novato (Marin Co.) (i.e., Alameda del Prado exit from Hwy. 101...west side of highway across from Hamilton Field.) Yes, as you may already know, this non-breeding season resident of Marin Co. (per the latest 2024 Marin County Breeding Bird Atlas 2 report as one source) is common ...and periodically has invasions when it appears in our forest. NOT this past few months. Until the last week when I daily hear songs and calls of this species...and both males and females foraging in the early morning. Of the two subspecies for this species, I believe the one moving through is Ixoreus naevius naevius.... and their destination is noted at the Cornell Lab of Ornithology Status and Trends link per: https://science.ebird.org/en/status-and-trends/species/varthr/abundance-map?season=prebreeding_migration ( = a more typical interior subspecies is I. n. meruloides. ) Interested in more details details in relation to Varied Thrush's "Timing and Routes of Migration"....? If so: Per BirdsOfTheWorld.com, here's an excerpt for their late-winter/spring movement: Spring In coastal populations ( I. n. naevius ), often difficult to distinguish spring migration because of presence of winter residents throughout much of breeding range. In se. Alaska, where density of winter residents is low and arrival of migrants is easily distinguished, early migrants arrive in late Mar and continue to arrive through latter half of Apr (see Figure 5 ( https://cdn.download.ams.birds.cornell.edu/api/v1/asset/24991331?<__hstc...>&<__hssc...>&__hsfp=3783277660 ) ; Bent 1949 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF21684 ) , Gabrielson and Lincoln 1959 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF56655 ) ). Along north coast of British Columbia and Haida Gwaii, noticeable increase in number of Varied Thrushes in first and second weeks of Apr, with a peak in mid-Apr–early May. On south coast of British Columbia, noticeable movement during third week of Mar, with a peak in late Apr to first week of May ( Campbell et al. 1997b ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF64626 ) ). Little information about arrival dates of coastal breeders in Washington, Oregon, or California, but individuals may winter in lowlands and move into forests of coastal mountains to breed. In Seattle, WA, area, species is plentiful in winter months, lingering through mid-Apr ( Jewett et al. 1953 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF5025 ) ). In Oregon, birds return to mountain breeding areas in Mar and Apr ( Gilligan et al. 1994 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF56692 ) ). Departure dates from areas south of southern breeding range of naevius average mid-Mar for Santa Barbara Co. ( Lehman 1994b ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF55681 ) ), and early Apr for Monterey Co., CA ( Roberson 1985 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF21696 ) ). In much of its range, it appears that naevius migrates altitudinally from lowland areas to adjacent coastal mountains, but some north-south migration occurs as well. Interior populations ( I. n. meruloides ) exhibit a longer latitudinal migration, with a clear distinction between breeding and wintering sites. In interior British Columbia, main movement begins in early Mar with a peak in mid- to late Apr. Most individuals have moved through valley bottoms to higher elevations by first week of May ( Campbell et al. 1997b ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF64626 ) ). In Oregon, transients (possibly this subspecies) pass late Mar and Apr ( Gilligan et al. 1994 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF56692 ) ). Little information on migration dates in other interior locations. Early arrival dates in interior breeding areas outside of British Columbia, from south to north, are: 8 Mar in Coeur d'Alene, ID; 12 Mar in Banff, Alberta; 25 May in Forty-mile, Yukon Territory; 28 Apr in Fairbanks, AK; and 15 May on Seward Peninsula, AK ( Bent 1949 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF21684 ) , Kessel 1989 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF61012 ) ). Main wave of migrants usually follows early arrivals by 1–3 wk ( Kessel 1989 ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF61012 ) , Campbell et al. 1997b ( https://birdsoftheworld.org/bow/species/varthr/cur/references#REF64626 ) ). Regards, Daniel Edelstein Novato, CA WarblerWatch.com -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. 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