Wednesday, June 12, 2013

Americanish Oystercatchers: Hybrids vs. Frazari

Bird #1. A rather haggard black and white oystercatcher with a low black bib, with a lot of black "dripping" down its bib onto the upper belly. Although some many would be tempted to call this a frazari American Oystercatcher, it is a hybrid American X Black Oystercatcher. Ventura Harbor, Ventura, CA.

On much of the continent, ID of oystercatchers is a carefree and stressless task. You either have Black or American, or none at all. Simple. Enter Southern California, which has moderate numbers of Black Oystercatchers, and occasionally American Oystercatchers, which allegedly occur so often that they aren't even a review species anymore. The two species hybridize frequently, primarily in Baja California, but those birds regularly move north into California...giving us Black, American and hybrid oystercatchers to find. This is complicated enough, right?

At least Black Oystercatcher ID is not complicated. Looking at them does not inspire headaches, only love. Miller-Knox Regional Shoreline, Richmond, CA.

No. No it is not. It needs to be more complicated. Because the subspecies of American Oystercatcher here (frazari) is thought (by some) to look exactly what a hybrid American X Black Oystercatcher would be expected to look like. They are not really expected to look like the clean cut, palliatus Americans of the east coast. They are sloppy, smudgy, and have tons of black bleeding in to their white parts...or so some have been lead to believe.

So how can you tell a hybrid from a frazari American Oystercatcher? Is there even a difference? Are frazari oystercatchers just hybrids, and nothing more? Well, with the way some birders think of frazari as appearingthere really isn't a difference (i.e. in the latest edition of the National Geographic guide, which is quite unhelpful in this instance). But if one is a bit more conservative in their approach (i.e. not stringy), the differences begin to appear.

This is where I am obliged to mention the vaunted "Jehl Scale", which birders take very seriously. If you're not familiar with it, go take a peek. I think it's a good idea and is widely accepted by high-ranking birders, but it is just begging to be misinterpreted. Stringers love using the Jehl Scale, because they can magically turn hybrids into pure birds while sounding like an expert. Put a bunch of birders together and you will likely get all sorts of different Jehl scores for the same damn bird. You also need very good looks/photographs of the bird in order to score it accurately.

My opinion? To put it simply, many so-called frazari in California should simply be called hybrids. The birds with a high black "bib", little to no black in strange places, and only a little smudging on the sides of the bib are good for frazari. It should be noted that other populations/subspecies of American Oystercatcher, such as those in the Galapagos Islands (galapagensis), have a slightly uneven bib as well, so this is not just something to be expected in hybrids.

Yeesh, what a mess. Let's just look at some birds, shall we?



Bird #2: A typical hybrid oystercatcher, albeit a whiter one than Bird #1. The Ventura Harbor has been one of the easiest places to see hybrids in California the last couple years. That said, the Ventura Harbor has been one of the easiest places to string an American Oystercatcher the last couple years, if you get my drift. Photographed at Ventura Harbor.


Note dark mottling under the wing and under the tail, dark flecking on the belly, extensively dark uppertail and black rump...all strong hybrid marks. By the way, I want to give props to the diligent eBird reviewers who have kept misidentified "Americans" from the Ventura Harbor off of eBird.

Bird #3: Another hybrid. True, this photo is incredibly artistic, but I'm trying to show the dirty and broken u-shaped tail stripe. This belongs to pretty mixed-up bird (genetically). Morse Point, Santa Cruz Island.


The same bird as above. A very striking individual; the dark blotches on the axillaries and breast band extending well into the belly (among other things) put this bird firmly into hybrid territory.


Bird #3, at rest. This is on the heavily-marked side of Americanish oystercatchers that show up in California, many are not as striking.




Bird #4: Morse Point, Santa Cruz Island. At first I thought it was the same American Oystercatcher that I had located at the same site previously (see Bird #5) until I noted that it was an adult (adults have all orange-red bills, immatures have a dusky-tipped bill). The breast band was somewhat lower on the breast as well, and less white was visible above the folded wing.


Bird #3 is on the left, Bird #4 on the right. Note the more white on the tail/rump of Bird #4, and wider white wing stripe.


Scoring Bird #4 very conservatively (using other photos as well), the Jehl Scale gives it a 31. That's a pure American Oystercatcher right there, despite the suspiciously narrow wing stripe and narrow tail band infused with dark feathering. At least, that's what Jehl thinks it is. Me? I'm not convinced. I have no doubt that many birders (including good ones) would tick this as an American, but I personally feel like there are too many Black Oystercatcher genes getting expressed.



Meet Bird #5. The bird on the right had been present near Morse Point on Santa Cruz Island since early April, and appears to be staying for the summer. It has the high breast band typical of American Oystercatchers (sitting higher on the breast than birds 1-4), with a very limited amount of smudging near the bend of the folded wing, as expected in frazari.  It closely resembled American Oystercatchers I have seen in the Gulf of California, which do not have a mysterious genetic makeup; hybrids do not occur there.




This angle shows the high and unragged black bib line, as well as the clean white flanks, axillaries and underwing expected in frazari. The undertail coverts are a pristine white as well.


Note the broad width of the wing stripe and tail stripe compared to Bird #4. This bird has a little bit of dark mottling in  the white of the tail band, but it is limited and does not bisect the tail/rump. Out of the many American Oystercatcher candidates I've seen in California over the years, this is the only one that I feel really fits the frazari bill. And if you are wondering...this bird scored a 39 on the Jehl scale.

So do all American Oystercatchers in California have Black Oystercatcher genes? It's possible; there is no concrete evidence either way. The American Oystercatchers at the Salton Sea in the 1970's most likely came from the Gulf of California, where hybridization does not occur (a photograph of a couple of those birds is on Don Roberson's page here). I think that's something we should accept though; frazari birds that show up here likely have some Black Oystercatcher genes, but that doesn't mean we should count all hybrids as American Oystercatchers, or not count American Oystercatchers at all.

If you would like to learn practically everything there is to know about American Oystercatchers, the American Oystercatcher Working Group is an excellent resource. And if anyone knows where to find Jehl's classic paper online, please let us know!

13 comments:

  1. Until today I had never heard of frazari, I guess that is because I haven' photographed Oystercatchers (of any species) in California and now I realize that if I do I might get a headache trying to figure them all out.

    Thanks for the education Seagull.

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    1. It is a headache. I reckon people should assume a black and white oystercatcher here is a hybrid, and if warranted could then try to convince themselves otherwise (its usually the other way around).

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  2. My students have their genetics final today so this got me thinking ...

    So it seems like it may be easyish to figure out an American X Black where one parent is pure for each species, but then what happens when that 50:50 bird mates. Could bird 4 be a hybrid that mated with an American giving a 75%American:25%Black? And it is easy to imagine it can get way more complicated that that.

    Is there anything known about mate choice in hybrids? Are they sluts that will just mate with any species that comes by looking for some action or do hybrids prefer to mate to Americans more than Blacks? Is there any sexual bias in this?

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    1. Oh yeah. Your bird 4 theory is certainly possible...I think backcrosses are definitely out there.

      Mate selection of hybrids is not well-studied, although the elusive Jehl paper likely addresses it. Since most of these birds seem to breeding in Mexico, there aren't many people observing what happens during the breeding season.

      Roberson (paraphrasing Jehl I assume) says that Blacks and Americans used to occur along western Baja together and did not interbreed; it was only after these birds were wiped out and new colonizers arrived (of both species) that rampant interbreeding began; this was a result of a lack of potential mates of the same species.

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    2. Thanks for the info. I will try and find and actually read this elusive Jehl paper.

      First rule of genetic: When in doubt always backcross to wild-type, although I am not sure which one is WT in this situation. Unless the hybrids are sterile (doubtful in my mind, but maybe the answer is already known) then backcrosses have to be out there just messing with the birding world.

      That being said, reading your blog has taught me the very important lesson of being more conservative when calling birds. We just don't get hybridization like this in the reptile (and mammalian for that matter) world. Reptiles also don't travel the distances that birds do looking for a mate, which I can imagine limits their ability to hybridize in the wild.

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    3. Although a lot of hybrid combos are possible, not many are actually very common once you leave the realm of gulls. I could bird for a month straight and not see more than one or two non-gull hybrids...but they are out there.

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  3. The Jehl paper is available here if you know anyone with university/library/AOU access.

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  4. A 2004 paper says: The close COI similarity of American and Black Oystercatchers revealed in this study is consistent with suggestions that these are allopatrically distributed color morphs of a single species (Jehl 1985). Identification of Birds through DNA Barcodes.

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    1. COI=?

      What paper is this Mark? Not a shocking finding, although off the bat I don't know if I agree with it.

      The high-ranking birder known as Red Phalarope Man poo-poos the use of DNA barcodes as an accurate method of gauging genetic divergence in birds. Thoughts?

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    2. Jehl never says in his 1985 paper that they are color morphs of a single species. As a matter of fact, his concluding paragraph states

      "It appears that the distribution of oystercatcher phenotypes on the Pacific coast of Baja California existed in a stable condition at the turn of the century and that in most localities the pied and black forms acted as separate species. At San Roque/ Asuncion and on the mainland coast south to Cabo San Lucas, however, the small populations may have been interbreeding freely. The situation was disrupted by intensive collecting, but local populations have since become reestablished at or near their original composition. From this I conclude that selection promoting the presence or absence of a particular phenotype at a specific location is strong. The resumption of the original condition, and the demonstration of a high frequency
      of assortative mating in current (and, by inference, in original) populations, as well as of a low frequency of hybrids in both original and current populations show that bachmani and palliatus are independent evolutionary units and must be considered as specifically distinct."

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  5. Thanks for this. I spotted a hybrid from the Island Packers boat in the harbor yesterdayhad no familiarity with their occurrence in Ventura. I have seen Black Oystercatchers in LA and SLO coastal area so was unprepared for the hybrids in Ventura.

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    1. Glad to be of service Laura. Hope you had a great trip! This weather has been ridic lately.

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