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Pacific Beach – apparent hybrid Grace's X Yellow-rumped Warbler, 09 April 2020

Over the past few weeks I have had several encounters with an unusual looking warbler from my patio here at my home lock-down situation in Pacific Beach.  I first cottoned on to this warbler because of its unusual sounding call – a slightly squishy "chip" or "chit" call.  It does not sound like any of the expected winter resident warbler species so had me really curious.  I eventually managed to run for my camera one day, 15 March 2020, and get started with some detailed documentation worthy photos.  So far I have had three photography encounters with it and yesterday, 09 April 2020, obtained close photos in nice flat gray late afternoon lighting.

After the first encounter on March 15 I realized that it was likely a hybrid warbler and started picking over the background literature on a few candidate species.  I believe this could be a Grace's X Yellow-rumped Warbler hybrid.  Several birders contacted me about the photos on eBird and also suggested the same potential hybrid parentage.  The call, behavior, and snap gut feeling for me pointed to a close similarity with Grace's Warbler but obviously not perfectly!  The call is very similar, perhaps indistinguishable from Grace's Warbler.  I will also note the behavior as it only seems to feed probing in pine tree branch tips, flies right past pepper trees and mature lemonade berry, never fly catching or coming down to the ground as you often see Yellow-rumped Warblers doing.  But the plumage characteristics do seem to have some clear Yellow-rumped Warbler features in the mix of things.  If you look carefully yellow on the chest sides, white eye arc, greenish-yellow rump belt, and a faint "coronation" of paler feathers on the crown.  Definitely a mixed up creature.  As I discovered from several sources (e.g. Dunn & Garrett, 1997, Warblers, and Curson et al. 1994. Warblers of the Americas) there is mention of a single record of this hybrid warbler combination found in Colorado.  I could not find much else on this Colorado record trolling through the internet but amazingly did discover a painting of the hybrid by bird artist Jon Janosik at this link 

http://www.natureartists.com/artists/artist_artwork.asp?ArtistID=1099&ArtworkID=13035 It does look similar although tail markings potentially different (white extends to tail tip in my bird, like Grace's Warbler, while white is only windows in tail in the painting, like Yellow-rumped Warbler).  Textbooks and Janosik's painting describes Audubon's Yellow-rumped Warbler parentage, I would assume the same for my bird but perhaps difficult to be certain.

I have posted photos of this neat looking warbler on a few eBird checklists.  I have not found any other photos of this apparent hybrid in eBird or searching through the internet.  Is definitely something to puzzle over.
Best photos on 09 April 2020 https://ebird.org/checklist/S66883389
OK photos 05 April 2020 https://ebird.org/checklist/S66753918
Nice photos on 15 March 2020 https://ebird.org/checklist/S65848692 with notes on the plumage, call, behavior
 

— 
Gary Nunn
Pacific Beach

Source: SanDiegoRegionBirding Latest Reports