Sunday, January 8, 2017

Our Three-day Side-trip to Tuxtepec

The highway north from Oaxaca City passes over two ranges of mountains that are sparsely populated and teeming with many species of little-studied plants and animals, and my Oaxaca at Christmastime tour takes a two-night break from the markets, ruins, and holiday festivities to indulge in pure birding and natural history bliss to travel over them to the lowland tropical town of Tuxtepec.

We depart at 5:30 one morning and drive nearly and hour and a half to our picnic breakfast spot along the tritely named Rio Grande. We first cross over the continental divide at La Cumbre Ixtepeji, where we’ve already birded twice, and drop down into the valley between those mountains and the Sierra de Juárez. Though the habitat in this valley is much more like the tropical deciduous forest and thornscrub of the Oaxaca Valley and the Pacific coast, we're actually in the Gulf of Mexico watershed – this river flows northwest at this point but downstream makes an abrupt righthand turn to pass through a narrow canyon in the Sierra de Juárez, exiting into the humid tropical lowlands by Tuxtepec. While no birds at home in those tropical lowlands have any interest in working their way up the canyon to this dry interior valley, several species of birds have crossed over the lowest pass in the continental divide to the northwest of Oaxaca City to populate this isolated habitat. We heard Happy Wren, saw a Oaxaca Sparrow, and had brief views of a Violet-crowned Hummingbird; there are also Rusty-crowned Ground-Sparrows, Orange-billed Nightingale-Thrushes, and many others here that would otherwise be unthinkable in the Gulf of Mexico watershed.

I suspect that many of the plants, much less capable of dispersing than birds, must be endemic to this valley. I’d also guess that this Echeveria sp. is one of them.

We made a brief stop in this valley on the way back and admired these Atta sp., leafcutter ants, one carring a petal from a Wigandia plant.

The Valle Nacional Cloud Forest, or the Gulf slope of the Sierra de Juárez, or Mexico federal highway 175 from Oaxaca City to Tuxtepec – whatever you call it, it is a gem of a road. This is a view from the mirador at the highest point on the Sierra Juárez looking north over an expanse of mindblowing diversity. (This was on our way back; on the way to Tuxtepec this was engulfed in clouds and a drenching drizzle.)

The higher elevations (over 9000 feet) are still clad in a temperate pine-oak forest, but there is a significant component of many unusual broad-leaved trees, and it’s much, much wetter than your typical Mexican pine-oak. Take for example this lush tree in the family Rubiaceae. It has been narrowed down for me as one of two species: Arachnothryx pyramidalis or Arachnothryx buddleioides by the Mexican botanist Alejandro Torres, and I suspect it’s largely pollinated by hummingbirds.

The orchid flora here is off the charts, though most bloom in the warmer months.  We saw but three species in bloom This one is Maxillaria cucullata, thanks to some keen orchid friends for the IDs.

This is Stelis platystylis.

A common roadside “weed” is this gorgeous terrestrial orchid Epidendrum radicans.

On our sunny return we even saw some butterflies, this one being a new one for me, Cyllopsis suivalens, Dyar's Gemmed-Satyr.

Farther down the road, the forest is even more lush, and the species diversity explodes.

At first glance I assumed this all dark satyr would be unidentifiable, as in my experience in the Andes there would be ten species that would look just like this from above. It turns out there are far fewer species of such temperate-zone satyrs in the Mexican cloud forests, and so this one must be Pedaliodes circumducta, Circumducta Satyr.

Same with this satyr, Pareuptychia ocirrhoe, White Satyr.

One more butterfly from the mid-elevations that was a real cloud-pleaser was this Philaethria diatonica, Northern Green Longwing feeding on a small tree-sized Poinsettia in a yard.

We had a full day in the tropical lowlands outside of Tuxtepec, though my favorite forest trail was occupied with wild rubber harvesters loading up their bounty into trucks. We found a nice side road nearby that passed through some pastures and led to a strip of trees that was hopping with birds. This Golden-olive Woodpecker was one of a pair that competed for our attention with a Gartered Trogon, Band-backed Wrens, and a Black-crowned Tityra.

We heard several Ferruginous Pygmy-Owls in response to my nearly continual tooting to bring in passerines, but one time both birds of a mated pair came in close (the larger and mostly silent female below the male).

We tallied a very high total of nine Roadside Hawks this day.

We made a stop where I had seen White-throated Flycatcher many years ago in an area dominated by sugar cane plantations and had a bird come in right on cue. This bird is in the genus Empidonax but is highly unusual in its entirely tropical distribution and open, marsh-like habitat preference.

At our first afternoon stop I mentioned that it might be good for Keel-billed Toucan, and when we got out of the van, one flew into a fruting Cecropia tree as if on cue. Ka-ching.

Surprisingly, there were rather few butterflies to be seen in the warm, humid, tropical lowlands. I came to the conclusion, based on the irregular forewing hyaline band and the five spots in the wingtip that this difficult long-tail was Urbanus tanna, Tanna Longtail.

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