| 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.
|
|
and now . . . THE
ANSWER TO THE MYSTERY
|
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." |
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photo
© BSOL
