Date: 6/29/25 6:48 am From: Johnson, Erik via groups.io <Erik.Johnson...> Subject: Re: [labird] Golden-cheeked Warblers overfly LA
Hi Peter and LAbird,
Thanks for sharing this. Very interesting. Having worked with light-level geolocator data, I can appreciate some of the uncertainties it generates, especially during migration. Latitude is notoriously harder to estimate with accuracy than longitude, and the difference between Louisiana and southern Mexico can be hard to distinguish with certainty, especially as the date approaches the equinox. To illustrate this point, I'm happy to share location data generated from light from a geolocator we recovered this spring from Amite River Wildlife Sanctuary. You should be able to click through the dates to see how locations and the precision changes depending on stopover duration and proximity to the equinox.
https://rpubs.com/Erik_I_Johnson/1301031
Back the Golden-cheeked Warbler paper. The figure with the 11 movement trajectories showing easterly fall migrations does not show the uncertainty, so it's hard to be sure how realistic these lines are. But interestingly, the date of the fall migrations reported in the paper spanned July 1 to September 3, which is a good bit before the equinox, and there are apparently some longer stopover durations (which helps improve accuracy), so it is a little harder to poke holes in the idea of an easterly movement in fall.
Such a "loop migration" pattern is exhibited by a number of Neotropical migrants, although many of those tend to be more boreal. There are even two recent documented records in eBird from late August in the Tampa, FL area (and also a specimen from late August in 1964), and early to mid-August Houston/Galveston-area records, suggesting the geolocator data showing the occasional trans-Gulf migration may have some validity. But I'd be surprised if it were as common as the paper suggests, given the paucity of records from the northern Gulf.
Golden-cheeked Warbler populations continue to decline, unlike the rapidly increasing Black-capped Vireo, which now has records from LA. Even so, there's no reason to think Golden-cheeked Warbler wouldn't show up from time to time, and I think this geolocator study helps reinforce that. This species would (will) be an amazing (and overdue) first state record, but I'd be hesitant to use light-level geolocator data to accept it as a first.
Erik Johnson
Sunset, LA
Erik.Johnson AT audubon.org
-----Original Message-----
From: <labird...> <labird...> On Behalf Of Peter H Yaukey via groups.io
Sent: Sunday, June 29, 2025 7:35 AM
To: LABIRD List <labird...>
Subject: [labird] Golden-cheeked Warblers overfly LA
LABirders:
I read a (to me) shocking geolocator paper yesterday that reported that many Golden-cheeked Warblers travel far east from their nesting areas before turning south in fall, many apparently traversing Louisiana. The paper states that 20% of the birds in the study sample migrated across the Gulf in fall, including some going as far east as peninsular Florida. Here are the tracks of the c. 12 (of their total of 61 migrants tracked w geolocators) that went transgulf or through Florida.
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They had another map that gives stopover points. One of these is on the Chandeleurs. Has the LBRC considered whether a geolocator observation could constitute a first state record? The lead authors of the study are actually at LSU- perhaps they could provide information on the amount of precision in that stopover observation or the flyover tracks?
This is crazy!
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