Re: "Costa's" Hummingbird - an F2 hybrid?

Peter Pyle

California Bird Records Committee has been wrestling with this interesting question. Lately it has regarded Blue-winged Warblers in the state, few of which seem absolutely "pure," especially if phenotypically "pure" individuals may (or even likely) have genes from the alternate species. I've been advocating for a 7/8th threshold to consider an individual pure, e.g., F3 with 7 of 8 grandparents of one species. This would of course still involve a judgement call but it seems to be a better line to draw than one we can't even see.

Speaking of HERG x GWGU, SF birders, there was a good mixed gull flock this morning across from the SF Water Treatment Plant on Great Highway. Dominated by GWGU but many HERGs, some THGUs, and I'd say at minimum 5-6 HERG x GWGUs, likely more.

Good birding,


At 10:10 AM 1/6/2021, Adam Winer wrote:

On Wed, Jan 6, 2021 at 9:57 AM Alvaro Jaramillo <<mailto:chucao@...>chucao@...> wrote:

Adam et al.

Fascinating! But it proposes a philosophical question. What is pure? A large proportion of Townsend's Warblers have Hermit Warbler mtDNA from historical swamping of the northern portion of the historical range of Hermit (which went into Canada). Similarly many populations of western White-crowned Sparrows share identical mtDNA with Golden-crowns. And lets not even get into the gulls! So given that eBird requires you check a box and add a number, and people’s lists require that only "full species" be counted. What is the cut-off for what is acceptable on a list? I mean if you want to get strict about it, I bet that a sizeable number of the Thayer’s Gulls (Iceland now) reported in the state are likely hybrid Herring x Glaucous-winged, as that is not a bird that is on most people's radar. By sizeable, who knows maybe a quarter of them???? If you expand it to gene pools, as good species, there are many a good species which incorporate genes from adjacent species, are of hybrid origin, or have a bit of rogue DNA running around (I forget how much Neanderthal DNA I have from the 23andme results, but it is sizeable compared to the average population, and anyone who knows me would have predicted that).

     I don’t think there is an answer, but it is worth pondering. But if anyone is looking for absolutes, and “purityâ€&#65533; perhaps anything associated with biology and the real living world is not the place to be looking for that 😊.

Oh, absolutely - any notion that hybrids are "lesser" is silly, and should have last been acceptable around the time of Plato. I also surmise that once we get past very well-known phenotypes like "Brewster's" Warbler (or chicks seen emerging from mixed parentage nests), that these hybrid IDs are (at best) highly educated guesses, particularly when we're defining endpoints for "this is pure" and "that is not".

I'm also relieved that I had a female/immature Costa's Hummingbird on Mt. Davidson a few years back. So I don't need to worry about my city list here. I'm confident that was a pure Costa's because [STATIC, RECORDING ENDS].

More seriously, I've learned a lot more than I would have with an unambiguously pure Costa's. But now I have to figure out what to tell my kiddo to do with their lifer "Costa's" Hummingbird!

-- Adam



Alvaro Jaramillo



From: <> <<>> On Behalf Of Adam Winer
Sent: Wednesday, January 6, 2021 9:29 AM
To: SF Birds <<>>
Subject: [SFBirds] "Costa's" Hummingbird - an F2 hybrid?


An update on my backyard hummingbird!


First off, it's still present today, and apparently is also being seen at hummingbird feeders at a home backing onto the "wild" area at the intersection of Cesar Chavez and Noe. I have no idea about actual public access to that plot of land, and you're looking into people's homes, so great care is needed if anyone tries via that path.


Second, and more interestingly, the identification of this bird has gotten really interesting. There's a long discussion on Facebook (<> but to summarize things that have been discovered since I first posted:
This bird gives both Costa's and Anna's Hummingbird songs. It's worth pointing out that this alone does not prove it's a hybrid, as hummingbirds (and specifically Costa's and Anna's Hummingbirds) can and do learn songs even as adults. But It's perhaps unprecedented to have one bird singing both!
This bird, in some lights, shows a very pink cast to the gorget (though at other times is glowing purple.) I've attached one such pink photo to this email, which also shows tail structure very well - there's others on eBird. (The question of "how pink is too pink" is still open.)
David Rankin (who's specifically studied Anna's x Costa's hybrids at UC Riverside) wrote "The tail feather shape seems very Costa’s-like, but r4 and r3 seem a bit thicker than normal. The gorget color is hard to interpret. I like this as a f2 backcross with Costa’s (3/4 Costa’s, 1/4 Anna’s).".


This is all fairly mind-blowing - what are the odds that the first "Costa's" male in ages is a hybrid with 3 Costa's grandparents?!? And what does it say about the previous records of female/immature Costa's in SF? (I can't fathom an F2 female/immature being identifiable, and an F1 would be an enormous challenge if feasible.)


Big thanks to some of the birders (Ethan Monk, Lucas Stephenson, Jonah Benningfield, to name a few) who took a look at the pictures of this bird (or listened to it in the field) and saw "something is off".


If anyone encounters this bird in the field, please do try to get as much audio of it as possible (ideally accompanied with some photos so we know it really is *this* bird).



Adam Winer




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