Annotated checklist and data resource
text © Don Roberson
photos copyrighted by photographer(s) credited
all photos taken in Monterey County, California
mystery warbler
photo © D. Roberson
Ventana Wildlife Society's Big Sur Ornithology Lab captured this bird at the Big Sur R. mouth, in Andrew Molera State Park, Monterey Co., California, on 20 Sep 2006. It was weighed, measured, and studied in hand by BSOL staff and interns, including Jessica Griffiths, Matt Brady, Ryan Terrill and others, and visitors, including Rita Carratello, Steve Larson, and Don Roberson. None of us could identify the bird; our best estimates were a hybrid parulid warbler. Various combinations were proposed, some of them intergeneric. [My personal guess was Common Yellowthroat x Yellow Warbler.] Comments are welcome. 

Since the bird was not identified, it could not be banded under protocols. It was released but two rectrices were retained for possible DNA evaluation.

In the shot below, it is next to an imm male Common Yellowthroat, to show color tone and structure. When released it gave a zingy zeeet flight note, recalling Yellow Warbler but a bit rougher and possibly deeper.

These biometrics were taken by BSOL in hand. More details on wing morphometrics are available on request:

Wing = 60
Tl = 39
Exposed culmen = 10.51
Nares to tip = 7.53
Tarsus = 15.43
Bill depth = 3.07
P8-p6 = emarginated

photo © D. Roberson

photos © BSOL
photo © D. Roberson
photo © BSOL
photo © BSOL
Undertail coverts with dark subterminal spots.
photo © BSOL

Walter Messier, Ph.D., Evolutionary Genomics in Aurora, Colorado, performed DNA sequencing on the genetic material obtained from the rectrices. The mother's identity was determined with full confidence via mitochondrial genes. The father's identity is less certain (for reasons set out below) but some species can be excluded. The most likely ANSWER is:

Mother = Yellow Warbler
Father = most likely Common Yellowthroat

The possibility that it was a very odd Yellow Warbler (both mother & father Yellow Warbler) cannot be excluded [see below], but it is Dr. Messier's opinion that the evidence best supports the intergeneric hybridization of Yellow Warbler and Common Yellowthroat. This hybrid has not previously been reported (e.g., Dunn & Garrett, 1997, Field Guide to Warblers of North America). Big Sur Ornithology Lab will be publishing a note on this bird.


Dr. Messier writes: "Now, as to the warbler’s father: this is more difficult, for two main reasons. First, as you know, we can determine the mother by using a mitochondrial gene. There are many many copies of each mitochondrial gene; thus PCR amplification (and the subsequent DNA sequencing) of mitochondrial genes is straightforward, even easy. As you know, mitochondria are inherited through the mother, so in order to learn about the father we must use some type of nuclear marker. Nuclear markers are single-copy genes, hence trickier to amply if the template quality is suboptimal (as can happen with feather-derived DNA). Second, and more important in this case: in contrast to mitochondrial genes, there are relatively few nuclear gene sequences from multiple species available in the sequence databases for birds, so even when we can successfully amplify a nuclear gene, we may not find any sequences from other warbler species to compare against. When in rare cases, a gene sequence is represented in the database by a number of species, that sequence is usually nearly identical in all those species and thus not very useful for distinguishing between species.

In this case, we used the nuclear c-mos gene (a proto-oncogene), one of the few nuclear genes for which any warbler sequence exists. But because this gene is almost identical in nearly all warblers for which sequence has been collected, we can at best exclude some species as the putative male parent. The sequence we obtained is consistent with both Yellow Warbler (already known to be the maternal parent by the mitochondrial evidence) or Common Yellowthroat. This inexactitude stems not from any failings of the technology, but rather from the incompleteness of the genetic database at present (at least for warblers. Organisms with more relevance to human medical concerns of course overrepresented in the databases! We are a self-obsessed species.) As so many warbler species are not found in the database, we can’t exclude all other likely or at least possible species, but we can with high confidence exclude species for which c-mos sequences do exist. The list of excluded species includes: MacGillivray’s Warbler, Black-and-white Warbler, Prothonotary Warbler, and Northern Parula. Again, these are not necessarily likely species (some, I think, are quite UNLIKELY), just those that we can exclude by analysis of available DNA sequences.

So for the father we fall back on what you and the Monterey area birders have already done: look for clues based on appearance. In fact, my first guess at parentage when I saw the photos was that, based on structure, one parent must have been a Common Yellowthroat. The nuclear gene data is consistent with that.

So we know quite definitely that the mother was a Yellow Warbler, and there are two strong possibilities suggested by the nuclear data. For my money, this bird is likely an intergeneric hybrid between Yellow Warbler and Common Yellowthroat. I checked the literature, and it doesn’t appear that this hybrid has been reported before."
Use the following links to other portions of the MTY checklist:
Part 1: Waterfowl through Grebes
Part 2: Albatrosses through Frigatebirds
Part 3: Herons through Cranes
Part 4: Plovers through Sandpipers
Part 5: Jaegers through Alcids
Part 6: Doves through Woodpeckers
Part 7: Flycatchers through Larks
Part 8: Swallows through Pipits
Part 9: Waxwings through Warblers
Part 10: Tanagers through Sparrows
Part 11: Grosbeaks through Finches
or just the plain Checklist (no annotations)
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Page created 21 Sep 2006, updated 6 Apr 2007