Sighting Record for Utah

Common name:	Chestnut-sided Warbler
Scientific name:	Setophaga pensylvanica
Date:	5-29-2022
Time:	Noonish
Length of time observed:	15-20 minutes
Number:	1
Age:	Adult
Sex:	Male
Location:	Willard Bay State Park - Willow Campground Site #140
County:	Box Elder
Latilong:	41.418407, -112.053493
Elevation:	~4,250
Distance to bird:	20 ft
Optical equipment:	Leica Ultravid 8x42 HD and Canon 7D Mark II with 100-400 mm lens
Weather:	Overcast with mixed showers, 50 degrees F
Light Conditions:	Poor
Description: Size of bird:	~5 inches
(Description:) Basic Shape:	Warbler
(Description:) Overall Pattern:	White, Chestnut, Black, Yellow
(Description:) Bill Type:	Thin, warbler like
(Description:) Field Marks and Identifying Characteristics:	Towards the end of a failed attempt at refinding the reported SCTA, Bryant and I started walking back towards the car at the north end of Willard Bay State Park. We were one campsite south of the campground host's site, when through the cacophony of singing Yellow Warblers, Gray Catbirds and freeway noise I picked out a different warbler song. Initially I knew it was different and didn't sound like any of our typical Utah Warblers, and once I alerted Bryant he was able to pick out the song too. Bryant was able to get eyes on the bird a couple times and in terrible light, and he initially said it looked black and white, but mostly white underneath. After a few more minutes he got a better look and called out "It's a male Chestnut-sided!" We called a couple other birders over to help us keep eyes on the bird, and spent the next 20+ minutes watching it and attempting to get documentation photos. This bird drove me crazy for a couple of reasons. I am very familiar with Chestnut-sided Warblers and their song, which really caught me off guard as it sounded nothing like the typical "very very pleased to meet you!" song variants, but more of a buzzy indistinct warble of a YRWA (like this:https://macaulaylibrary.org/asset/242437531). I had never heard that song variant of a CSWA. Back in the Midwest CSWA are everywhere - they like 2nd growth forest which is very common with all the logging activities in that part of the country. I have seen and heard 100's of these guys on territory, but I have never seen them sing in vegetation above a height of about 10 ft. This bird was up in the canopy, from about 15-30 feet high. Both the song and the height at which it was singing really threw me a curveball. Viewing from directly below - the bird was almost entirely white from throat to vent, extending further into white undertail coverts with dark outer tail feathers. The chestnut sides were visible from below, but color appeared blackish except when the bird popped out of the dark light. Black malar and eye stripe were visible, and when the bird turned its head from time to time you could get brief glimpses of the yellow cap/crown. See photo. (see photos)
Song or call & method of delivery:	Faint, somewhat buzzy warble without much fluctuation in pitch or emphasis of notes. Fairly subdued and quiet, hard to hear over much louder YEWA's in close proximity. Sang every 30 or seconds or so over about 10 minutes, stopped singing for about 5 minutes, and then sang again every 30 seconds from another 10 minutes or so.
Behavior:	Actively foraging/gleaning insects from foliage and singing 15-30 feet up in mixed deciduous trees, Cottonwoods and another species of tree I didn't identify at the time of sighting.
Habitat:	In canopy of mixed Cottonowoods and other trees, fairly close to a stream with some thick understory.
Similar species and how were they eliminated:	Clean white underside from throat to tail eliminates all other warblers except maybe Cerulean, Blackpoll and Tennessee. Chestnut flanks eliminates other species (Cerulean has faint dark streaking, Blackpoll has black streaking with on upper throat below bill, any color to the flanks eliminates Tennessee). No other species has the combination of black and yellow on the head. Since I didn't recognize the song - once we were able to visually confirm CSWA we were able to find a sound recording that matched the song variant we were hearing.
Previous experience with this & similar species:	Lots of experience with CSWA. Lots of experience with Tennessee, and some experience with Blackpoll and Cerulean.
References consulted:	Macaulay Library recordings, my co-observer Bryant, memory.
Description from:	From memory From photo(s) taken at the time of the sighting
Observer:	Max Malmquist
Observer's address:	2377 East Boyes Street
Observer's e-mail address:	**
Other observers who independently identified this bird:	Bryant and I were together and initially identified the bird, Quinn Diaz and Jack Binch (?) came by and saw the bird with us. Many others after the initial sighting (David Wheeler, Lauri Taylor, Vivian Schneggenberger, Mary McGreal, Matt and Darren Pendelton)
Date prepared:	5-31-2022
Additional material:	Photos
Additional comments:	Max and Bryants Checklist: https://ebird.org/checklist/S111633527 Quinn Diaz's Checklist: https://ebird.org/checklist/S111641211 Lauri, Viv and David's Checklist: https://ebird.org/checklist/S111732610 Mary's Checklist: https://ebird.org/checklist/S111720259 Matt and Darren's Checklist: https://ebird.org/checklist/S111739310