[texbirds] The Issue of Origin (LONG)
- From: Ted Lee Eubanks <tedleeeubanks@xxxxxxxxxxxxxx>
- To: texbirds@xxxxxxxxxxxxx
- Date: Thu, 31 May 2012 13:04:36 -0500
For those weary of this discussion, I apologize in advance. For those who
have participated, thanks for such an open debate. I can't say that this
issue is important to our economic revival or to world peace, but birders
certainly attach a certain gravitas to what is and what isn't counted.
All that we know for certain is that birds appear in unlikely locations.
This is certainly true for us in Texas. The black catbird, tropical
mockingbird, Yucatan vireo, white-crowned elaenia, and greenish elaenia are
but a few examples. We know for certain that these species appeared within
our boundaries. As for their provenance, we know nothing.
The discussion over the past several days has been long on speculation yet
short on facts. The various guesses and suppositions have begun to blend,
leaving the reader with the impression that these opaque presumptions
somehow bolster each other. Sadly, they don't.
Here is a prime (and obvious) example. The fact that a bird is kept in
captivity is unrelated to the possibility that it arrived by ship. Unless
someone can prove to me that trade birds other than parrots are being
transported via ship, then these need to be considered independent
variables.
Let's look at the first variable, the odds that a bird from the markets
finds its way to (1) Texas, and (2) Sabine Woods. So exactly what are the
species being sold?
Jay mentioned that the experts believed tropical mockingbirds to be sold
more commonly than other species. I disagree, based on the bird markets
that I have visited in Mexico and Meso-America. Are they commonly sold?
Yes, where they are available. But birds such as northern cardinal,
northern mockingbird, painted bunting, orange-breasted bunting, and lesser
goldfinch are seen more commonly. Birds often seen include clay-colored
thrush and brown-backed solitaire. Assorted jays and orioles are sold as
well, based on where the bird seller (pajarero) is located and from where
he is supplied.
Unexpectedly, the vast majority of the birds trapped and sold are destined
for the Mexican market. Experts estimate that at least 90% of the parrots
captured are sold into the Mexican market. In fact, the Mexican parrot
demand has grown to a point where at least 100,000 additional parrots are
imported from other countries.
And what about other trade birds? We know that around 6000 painted buntings
are sold each year to European collectors. But otherwise the birds are kept
within the domestic market. Yes, some may find their way across the border,
and we should (and do) see the density of those suspect birds being related
to how far you are from the border. Yet we count blue mockingbird,
clay-colored thrush, green parakeet, and red-crowned parrot even though
they are sold in nearby markets.
But what about a tropical mockingbird, a species found only south of the
Isthmus? This bird would need to have assistance to the border, then help
to reach Jefferson County. The unobstructed flight distance from Cozumel to
Galveston is around 800 miles. Which is more likely?
What about ship assisted transport? I loved the map of the various ships at
sea, but, of course, only a handful of these have any relevance. Let's
consider a few of the birds that we know have appeared in our state that
might be comparable to the tropical mockingbird:
Black catbird
Yucatan vireo
Greenish elaenia
White-crowned pigeon (sight record only)
Double-toothed Kite
Where do all of these occur together (a possible source for our birds)? The
Yucatan, in particular the eastern side of the peninsula (including
Cozumel). Some of these records date well before the advent of cruise ship
traffic between the Yucatan and Texas. These birds are not kept in
captivity or sold in the markets. Other than cruise ships, what ship
traffic exists between the eastern Yucatan and Texas (the oil fields are in
the Bay of Campeche, the other side of the peninsula)? I agree that oil
platforms could be a way in which birds could hop scotch their ways to
Texas. Does that make the record illegitimate? If so, then what about all
of the common migrants that also rest on these platforms? How do you know
if your lifer bay-breasted warbler took a respite on an oil platform just
days before you saw spotted it in High Island? Does it still count?
The argument about migratory tendencies is similarly weak. Some of the most
impressive territorial expansions in the past few decades have been made by
nonmigratory birds. Want a few examples? Try Inca dove, white-winged dove,
cattle egret, house finch, and Eurasian collared-dove for starters.
Carolina wrens have spread in the northeast by hundreds of miles, and they
are considered to be among the most sedentary of species.
Accompanying the Carolina wren in this northeastern expansion has been the
northern mockingbird. Prior to WW II the range of the mockingbird remained
from southern Maryland south. Over the next few decades the bird expanded
north as far as Canada. People have speculated that the planting of
fruiting plants such as the multiflora rose has allowed the mockingbird to
survive winters in the north. However, what inspired the mockingbird to
move north in the first place? In Canada, there is evidence that the
mockingbird has developed the ability to migrate, at least short distances,
to escape the harshest periods of winter. And we always thought this
species to be sedentary.
Yes, migrants do become disoriented. Yes, some that should fly south go
north. But there are expansionary species whose movements we cannot predict
and for which we have no explanation for their expansion in the first
place. We speculate, for example, that buff-bellied hummingbirds and great
kiskadees (both essentially nonmigratory) are expanding north due to the
loss of habitat in Mexico. Really? I believe it more likely that a
combination of mild winters and expanding (and maturing) urban forests
along the coast are more likely. Whatever the reason, they are expanding.
Want another example? Black-bellied whistling-duck. The bird is
nonmigratory (or shifts short distances). I saw the first bird to appear in
Houston, a bird that came in summer in the 1970s to the Uncle Ben's Rice
factory out off of Westheimer. That's right; the first pioneer
whistling-duck came alone. How do we know that the tropical mockingbird is
not similarly a pioneer, a wanderer? Surely none of us believes that the
800 flight miles are a hindrance. Once out of sight of land, what keeps a
bird from going forward when there is, for the most part, no going back?
The vast majority of Yucatan birds have no inclination to expand or to
wander. But what if one does, like the Yucatan vireo? The chance of this
bird becoming established is virtually nil since the breeding population is
far away and only one bird made the trip. But what if you see that one
bird, that first bird? What if you found the first Inca dove in Houston in
the 1950s? What if you came across the first white-winged dove on the
Freeport CBC? What if you discovered the first hook-billed kite that took
up residence in Santa Ana NWR? There was no precedent for any of these, yet
we now know they were precursors to a trend.
Hell, I remember when the downy woodpeckers irrupted from the woodlands of
east Texas and took up residence within the coastal hiatus. The downy is
supposed to be a sedentary species, and they were not in the woods at High
Island, Sabine Woods, or Galveston before. C.E. Hall records the dates when
birds made it from the mainland to Galveston Island, common species such as
the blue jay and the northern cardinal. Why did they move from the mainland
in the first place? Why did the crested caracara or the white-tailed hawk
make similar moves?
Whether 8 miles or 800, birds, even sedentary species, respond to a variety
of conditions and factors. At times their response is to move. Last summer
the Cassin's sparrows shifted their range east to the Katy Prairie. We
assume the drought provoked this movement, but, of course, we really don't
know. What we can say for certain is that there were no Cassin's before
(check the old breeding bird atlas) and suddenly they were everywhere.
Perhaps that is what I find most important about this discussion. Yes, bird
have wings and fly. No, they do not read the range maps. But more
importantly, birds are far more complex creatures than we give them credit
for. We assume far, far more than we know. If anything, I find the tropical
mockingbird to be humbling. Just when we think we have things figured out,
we learn that we have only just begun to learn.
Ted Eubanks
Austin, Texas
Other related posts:
- » [texbirds] The Issue of Origin (LONG) - Ted Lee Eubanks
