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Here we will show and discuss some apparent hybrid and-or intergrade
Petrochelidon swallows at Uvalde, Texas. This is roughly
75 miles west of San Antonio, Texas. These images I believe
support the fact that the hybridization between Cliff and Cave
Swallows (Petrochelidon pyrrhonota & P. fulva) does occur.
I found nests of four mixed pairs of Cliff (or Cliffish) Swallow
mated with Cave Swallow at a single site in 2011. Some of the Cliff
or mostly-Cliff-ish types and at least one Cave-ish type showed signs
of introgression in plumage (improper throat and auricular colors).
Two pairs lacked typical correct Cliff or Cave Swallow nest structure.
One cross-mated Cliff (and Cave mate) appeared pure (they were not
photographed) of the four mixed pairs. Of course to have intergrades
as the images seem to indicate, hybridizing of the parent species
The Cliff Swallows in this area (Uvalde County) are overwhelmingly
(almost all) bright creamy buff-white of forehead. Per Oberholser's 1974
Bird Life of Texas these are the tachina subspecies of
Cliff Swallow which was called Lesser Cliff Swallow. And which
(per Oberholser) can be various shades darker on forehead, some
nearing the color of Cave Swallow forehead apparently. This in
my experience is very very rarely seen in Cliff Swallows around
Utopia or Uvalde. Cliff Swallows here with anything darker than
bright creamy white "headlamps" seem scarce enough to make
one wonder if those odd individuals aren't intergrades.
Incidently at the site with the mixed-species Petrochelidon nests,
Barn Swallow is by factors the predominant nesting swallow, though
none I found were mated with anything but other Barn Swallows. There
were nearly a couple dozen pairs of Barn Swallows nesting at the site.
The only mis-mated birds at the site were Petrochelidon swallows, and
there were no pure pairs of Petrochelidon at the site. Perhaps biased,
but to this observer in these mixed pairs it seemed the smaller Caves
were the females.
Locally the two species nests are mostly well-separated by habitat
preference. Caves nesting (besides in caves) in culverts, Cliffs
largely nest on high bridges. Caves are now nesting under house eaves a
fair bit, usually where Barn Swallows do so, but I have seen no inter-breeding
with Barns in a few of those situations I found (Barn x Cave Swallow
hybridization is known). Interestingly I have found a few pure Cave
pairs nesting amongst Cliff colonies, with no apparent inter-breeding.
I have never seen a Cliff Swallow (or nest of one) in a Cave colony.
And I have been in more than a few culverts. Here the Petrochelidon inter-breeding
is not taking place in the parent species respective colonies, but in odd,
unusual, non-standard sites, such as in the case shown here, among a
Barn Swallow colony.
For reference only this is a standard adult (Mexican) Cave Swallow
with a buffy throat and rufous forehead. The nest is
interesting, semi closed to cieling. Unfortunately I never
ID'd the species of the mate. (taken at Garner St. Pk.)
In Texas the Cave Swallows are the subspecies pelodoma,
sometimes called Mexican Cave Swallow. This adult is
typical of those here.
Another reference shot, the bird on the right is our usual
Cliff Swallow with a bright creamy white forehead and dark
chestnut throat. Center bird is a Cave Swallow with buffy
throat and rufous forehead. The bird at upper left is a Cliff
(dark throat) with a slightly darker "headlamp" than Cliff
on right, presumedly acceptable normal variation for tachina ssp.
Most Cliff here are bright creamy white of forehead, rarely some
very few are darker. Apparently these are presumed to be pure birds.
~ ~ ~ Let the H-word fun begin ~ ~ ~
Here are three juvenile (yellow gapes) swallows in a nest.
Not a standard Cliff Swallow closed over jug style nest,
more like a decent Cave Swallow nest. The right hand bird is
fairly obscured, note center bird shows a pale throat and
dark auriculars (cheek-to-ear), throat on left bird is mixed
partly buffy and partly pale chestnut, again with dark auriculars.
Both have rufous foreheads.
Here is the right hand juvenile (yellow gape at right) with
mostly chestnut throat and auricular as it was being fed by
an adult to left. The adult has a buffy throat so is a Cave Swallow.
Here is the adult pair at the nest. The Cave is on the right.
On left the mate is Cliff-ish with chestnut in anterior (front)
of throat, but has a color break below eye turning to buff on
auriculars, indicating impurity. The forehead is actually admixed
as well with tract of rufous over bill. The rear auriculars are more
Cave buffy, anterior throat is Cliff chestnut. Just above nest rim
white underparts are visible.
Dorsal view, same Cliffish adult (flashed), which appeared to
be the male. The throat was chestnut anteriorly, fading
to dark buffy posteriorly into auriculars. Rump is on darker
side, like Cliff, tail shape is Petrochelidon.
One last pic of the lovely couple. I would call this
a Cave with a Cliff x Cave hybrid. And they appear
to be making Clave Swallows.
The above five pics are of one nest, as can be seen
in the various muds. Of the three young there is a
dark throated, a light throated, and a mixed color throat,
all with dark auriculars, and yo mama is a Cave Swallow.
~ ~ ~
Next is a different nest at the same site.
Here is a second nest at the same site. This bird has
pale underparts and a buffy rump (not a Barn). The throat to
auriculars are admixed, partly almost chestnut like a Cliff,
but there are buffy feathers along top of auricular and throat,
to center of throat below chin. Methinks a Clave Swallow;
an intergrade, or hybrid, Cliff x Cave Swallow.
The nest certainly is not any normal Cliff or Cave Swallow
nest, closer to some Barn nests I have seen. Forehead
was rufous like Cave. Mate is the bird below.
This is the mate to the bird above. It seems fairly
Cave Swallow though it appeared there was a little orangish
chestnut in auricular, a touch in throat. I do not think
it is a good pure Cave Swallow. I have never seen one with
orangish feathers in the auriculars.
~ ~ ~
Next is a different nest at the same site.
This bird is at a third nest at the same site.
The rich warm orange color in throat seems outside
limits for Cave, whilst the buffy parts of thoat are
not proper for Cliff. Auriculars mixed buff and dark,
forehead Cave type. This is likely another Clave Swallow.
I think the orange color here and on bird above is what
you get when you mix chestnut and buffy.
There were a pile of closed-eyed downy young not visible.
~ ~ ~
Above photos taken while standing in a shopping cart that refused to stay
in one place, twice rolling onto the auto door opener and then stopping.
If you find yourself standing in a shopping cart blocking the entrance of a
major retailer, with the auto-doors opening and closing, remember to always
appear like you know exactly what you are doing and are in total control.
~ ~ ~
Based on the above birds I believe we can be certain beyond
any doubt that Cliff and Cave Swallow are indeed interbreeding.
The three nests shown all have impure birds at them besides the
young they are generating. Hybridization is occurring between
Cliff and Cave Swallow and-or hybrids thereof. There are hybrid
or intergrade Petrochelidon swallows out there in the mix. A
fourth nest at the site had a pure appearing parents of each species.
I have not kept up with the situation at the site and do
not know if this continues. If in south-central Texas in
spring or summer and want to look, proceed to the east
entrance foyer of the Uvalde Wal-Mart supermegastore.
Which is at the east end of the megalopolis of Uvalde on Hwy. 90,
in the county of the same name, Texas. This is roughly 75 miles
west of San Antonio, Texas, at about 900' altitude. No
one said science would always be pretty. Check the high
drive-through pharmacy overhang as well, that is where the
pair with a pure Cliff and a pure Cave were. I apologize
for using foyer, and Wal-mart, in the same sentence.
So besides the apparent extreme variation possible in juvenile
Cliff Swallows (anywhere from buff to chestnut throats but always
with dark auriculars), we should expect any combo of throat and
auricular color to be found in Cliff x Cave Swallow hybrids and
their offspring. And they are out there. Obviously the throat
and auriculars is where we are most likely to detect anomolous
plumage that indicates interbreeding and a hybrid of these two
species. Until they get the bugs out of those DNA scanners.
Surely this happens far more than is known. There is less
than little coverage in many or most areas where it is most
likely to occur in summer. Such as near core historical Cave
Swallow breeding areas like the southern edge of Edwards Plateau.
Have you ever tried to find a birder here in July? I have seen
more hybrid Cliff x Cave Swallows. Habitats like these bigbox store
big high entrance overhangs did not exist before. They actually are
kind of cavey, and kinda cliffy. There went the neighborhood.
Incidently one of the earliest Arizona state Cave Swallows (in mid-'80's
at maybe a University (ASU?)) was at a nest paired with a Cliff Swallow,
but whether or not young were produced I don't know. Whether or
not mixed Cliff x Cave pairs (or pairs that include a hybrid thereof)
have been documented in Texas I do not know either. Obviously in the
first example with three young above, those are hybrid juveniles and fledging
is imminent, surely they were on the wing within days of the photos.
American Ornithologists Union, 1998, Checklist of North American Birds, 7th ed.
Oberholser, Harry C., 1974, The Bird Life of Texas, University
of Texas Press, Austin
Sibley, David A., 2000, National Audubon Society The Sibley Guide to Birds,
Alfred A. Knopf, New York
Turner, Angela, & Chris Rose, 1989, Swallows and Martins, An
Identification Guide and Handbook, Houghton Mifflin, Boston
Just for giggles...
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This is is not photoshop! At the precise 125th or 250th of a
second the shutter was open as I was taking a shot of the
bird on the nest, another bulleted by much closer to me.
The sensor grabbed about half of it as it shot by, and gave me
this single unaltered superimposed image of a Cliff Swallow
on a Cave Swallow. This is a metaphortagraph.
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