JIM CONRAD'S
NATURALIST NEWSLETTER
Issued from the valley of the Dry Frio River on the
southern slope of the Edwards Plateau, northern
Uvalde County, southwestern Texas, USA

February 2, 2014

PALE-LOOKING MOCKINGBIRD
Mockingbirds are common all across the southern two-thirds of the US, south through most of Mexico. Books call them Northern Mockingbirds to separate them from other mockingbird species farther south. They're MIMUS POLYGLOTTOS, the binomial neatly translating to “many-tongued mimic."

With regard to their mimicking, I can tell the story of how when I was a 15 year-old kid back on the farm in Kentucky, that summer I got my ham radio license and used Morse Code to talk with other hams all over the world. My radio shack was upstairs where it was hot, so the windows stayed open, and by the end of summer the mockingbird in the Flowering Peach just outside the window began adding Morse Code to his repertoire. He never said anything, of course, but he definitely sang properly spaced dits and dahs. Such a bird deserves its status as the state bird of Arkansas, Florida, Mississippi, Tennessee and Texas.

Around here mockingbirds are abundant year round, but they're not the laid-back feeder visitors I've known elsewhere. Here mockers are skittish, flying away when they see you. Note the wariness in the face of one I photographed this week at http://www.backyardnature.net/n/14/140202mb.jpg.

That bird is a lot paler and has much more white in its wing than birds I've been seeing both in the Yucatan and back East. In fact, three subspecies of the Northern Mockingbird are recognized, and this is the one I'm not used to. In the eastern US there's Mimus polyglottos polyglottos, and in the west Mimus polyglottos leucopterus. Texas has both the eastern and western subspecies.

In Texas the two subspecies intergrade in the eastern Edwards Plateau, near San Antonio, but we're in the western Plateau region, in the domain of the western subspecies. The Wikipedia mockingbird expert says that the western subspecies is larger than the eastern, but its tail is slightly shorter, its upperparts are more buff and paler, and its underparts are more buff, which is about what we see in our photograph. Also, the western subspecies' name "leucopterus" means "white-wing," referring to the big white splotch so prominent on our bird's wing.

In the Yucatan we had the Tropical Mockingbird, which my field guide called Mimus gilvus. Some experts lump that species with the Northern Mockingbird. You might enjoy comparing our pale mockingbird with a much darker winged Tropical Mockingbird photographed in Chiapas, Mexico's southernmost state, at http://www.backyardnature.net/chiapas/cenzontl.jpg.

*****

POTTER WASP POT
Beside the gravel road an Ashe Juniper branch at eye level bore among its branchlets the neat little dried-mud structure shown at http://www.backyardnature.net/n/14/140202pw.jpg.

A close-up better showing the structure is at http://www.backyardnature.net/n/14/140202px.jpg.

Even if you've never seen such a little mud urn perched on a tree branch like this, probably you can guess that it's the nest of a wasp, and that the wasp is closely related to the mud-daubers who build mud-tube nests beneath roof and cliff overhangs. This construction is much smaller and more elegant than those, however. It's the nest of a potter wasp, sometimes called mason wasp, Genus EUMENES, of which several species occur in southwestern Texas. Eumenes fraternus may be the most common and widespread here.

Like mud daubers, potter wasps are solitary -- don't form colonies. They sting many kinds of caterpillars, and sometimes beetle grubs, which paralyzes them, and then the prey is stored in a mud pot like that shown in our photo. The wasp then lays a single egg, attaching it to the pot's top inner surface. When the egg hatches, the larva feeds on the paralyzed, still living prey. The advantage of paralyzed prey over dead prey is that paralyzed prey doesn't decay. After the wasp larva pupates inside the pot the emerging adult breaks through the wall of the mud nest and escapes. Several generations can be produced per year.

Potter wasps are a little smaller than mud daubers, 3/8inch (2cm) to 3/4inch (3cm) long. The adult Eumenes fraternus is black with ivory markings on the abdomen and thorax, and feeds on flower nectar. Though potter wasps can sting if handled roughly, females don't defend their nests and aren't at all aggressive. In fact, for the service they provide of ridding gardens and fields of caterpillars, they're regarded as important and welcome citizens of the community, and never should be killed.

Our pot appeared to be empty, and there was no hole in its side where an adult had escaped. I wondered if it might be awaiting prey and an egg, maybe when warmer weather comes. Or maybe the pot had been so close to the road that a passing car disturbed the mother, causing her to abandon her work. It's known that mothers sometimes abandon their pots if disturbed while building them.

*****

DRAGONFLY NAIADS
In a shallow pool of the little Dry Frio River, when some blackened sycamore leaves sunken to the pool's bottom were stirred, a creature about ¾inch long (2cm) shot from among the leaves, settled at the pool's edge, grabbing onto a sycamore leaf's petiole. You can see the bug-eyed little fellow submerged in about half a finger of water at http://www.backyardnature.net/n/14/140202nd.jpg.

After taking that picture our discovery was coaxed into the palm of my hand, resulting in the picture at http://www.backyardnature.net/n/14/140202ne.jpg.

With six legs and no wings you might guess that this is an insect larva, and among the insects with big heads, large, widely spaced compound eyes and short, stiff antennae, and who hang around streams, what could this be but the larval stage of a dragonfly or damselfly? And since dragonflies and damselflies undergo incomplete metamorphosis where the larva emerging from the egg resembles a much smaller, wingless edition of the adult, the creature in the photo is a nymph. Moreover, nymphs of dragonflies and damselflies are known by the special name of naiad -- the word "naiad" rhyming with "pie ad." This particular naiad was obliging enough to allow the face portrait shown at http://www.backyardnature.net/n/14/140202nf.jpg.

In that picture, behind the head, you can see two tiny flaps, which are incipient wings, or wing pads.

The leaf-stirring exercise was so successful that I stirred some more leaves, and out shot several more aquatic-larva-type creatures, but only about half the size of our naiad, and very differently colored. You can see one at http://www.backyardnature.net/n/14/140202n1.jpg.

A shot from a different angle is at http://www.backyardnature.net/n/14/140202n2.jpg.

Were these two different species? Noticing that they shared similar patterning on their heads, I wondered whether the smaller one might be just a younger "instar." Remember that during incomplete metamorphosis, nymphal stages pass through a series of ever-larger, exoskeleton-shedding instars.

Volunteer identifier Bea in Ontario also suspected that the two naiad types were the same species. Moreover, she noticed that both early and late stages match other photos of naiads of the Common Green Darner, Anax junius, which occurs here, so that's our best bet for who we have here, but we can't be sure.

Whichever species they are, dragonfly naiads are known as voracious feeders who eat aquatic insects, especially mosquito larvae. Some large naiads even prey on small fish and tadpoles. They breathe through gills in their rectum, and when they need to move fast, as when they shoot from their cover of sunken sycamore leaves, they resort to jet propulsion by suddenly expelling water through their anuses.

*****

ISOPTERYGIUM MOSS
With wildflowers not blossoming and grasses with their flowering heads mostly disintegrated, obscure patches of life overlooked until now draw attention. For example, consider the modest smudge of mossy greenness at the base of a young Ashe Juniper on the dry hillside near Juniper House, shown at http://www.backyardnature.net/n/14/140202ms.jpg.

Since no spore-producing capsules are visible, and usually capsules are necessary for figuring out a species, at first I didn't think this moss was identifiable. However, its stems and leaves were so small that I hoped some especially tiny capsules might be present, so I lay onto the ground, put my nose right up against the patch, and by golly there were a few, only about 5mm tall (3/16ths inch), as shown at http://www.backyardnature.net/n/14/140202mt.jpg.

A couple of mosses were brought back to Juniper House, for it was certain that to figure out this one I'd need to look at microscopic details. For example, the shape of the capsule needed to be studied, and that's shown at http://www.backyardnature.net/n/14/140202mu.jpg.

The capsule is brown and nods downward atop its vertical stalk. In moss lingo, a nodding capsule is said to be "cernuous." The capsule is topped by a light brown cap, the operculum, with a bent peak. When the capsule is ready to release its spores, the operculum comes off and spores escape through a hole in the capsule's top. One slightly unusual feature of this capsule is that its top constricts just below its attachment with the operculum.

Two leafy moss stems and a reddish stalk are shown at http://www.backyardnature.net/n/14/140202mv.jpg.

Here we see that the moss bodies, instead of being short stem growing upright, as with many species, run along the ground with their tips curving upward. The leaves, only about 1.5mm long (1/16th inch), gradually taper to a sharp point. Many moss species have their capsule stocks issuing from the stem tip, but here we see that this reddish one arises from the stem behind the tips.

At http://www.backyardnature.net/n/14/140202mw.jpg you can see that the leaves margins are for the most part toothless, or "entire," though toward the tips sometimes very tiny, spiny teeth appear.

These are all worthy key features, but so far nothing had turned up really distinguishing this species from a lot of other very similar species. My last hope was to go in at a higher magnification to see the cell shape, shown at http://www.backyardnature.net/n/14/140202mx.jpg.Bingo! These cells, occupying a leaf's middle section, are very unusual. Leaf cells in most moss leaves are squarish, or rectangular, or roundish, and often the cell walls are thick and opaque. These cells are long and narrow, taper at both ends, and the cell walls are thin and fairly transparent. You might enjoy comparing these cells with those of a moss we looked at last month, the Controversial Weissia Moss, at http://www.backyardnature.net/n/14/140105mq.jpg.

Thanks to these remarkable cells and the comprehensive list of moss species listed for Uvalde County for Dr. Cynthia Galloway's South Texas Moss Project, our little tree-base moss reveals itself as ISOPTERYGIUM TENERUM, sometimes known as the Isopterygium Moss.

The online Bryophyte Flora of North America describes the Isopterygium Moss as occupying dry, wooded regions, swamps and wet roadside ditches, rotten logs, stumps, bases of trees, sandy soil, and rarely on sedimentary rock, so this is a very adaptable species. It's also widespread, occurring in much of eastern North America, south into South America, the West Indies, and in Italy. It's described as one of the most common mosses in Central Florida.

So, how about that? Winter botany at its best...

*****

ROSETTE LICHEN
Having identified most of our larger lichens, to find a species new to me I needed to start focusing on the smaller ones and, sure enough there they were, just waiting for me. One found this week formed fairly large, conspicuous colonies, but its individual, leaf-like bodies, or "thalli," were very small. You can see a pale gray colony covering a narrow ridge of bark on a mature Mesquite tree standing in the open at http://www.backyardnature.net/n/14/140202li.jpg.

In that picture you can barely make out the tiny, cup-shaped reproductive bodies, the apothecia, which don't grow larger than 2mm across (1/20th inch). A close-up showing how the apothecium spore-producing surface is pale gray at first but darkens with age is at http://www.backyardnature.net/n/14/140202lj.jpg.

At the bottom of this picture you can see the lichen's flat, leafy thalli, which branch as they advance across the bark, and which also are no wider than 2mm across. This foliose-type lichen has exceptionally small parts.

The smallness of its slender, flat thalli, its whitish gray color, the interesting way the apothecia spore-producing surface darkens with age, and its presence on tree bark, were important field marks enabling this lichen to be identified as PHYSCIA AIPOLIA. Because when species grows on broad, smooth patches of bark its colonies form expanding circles or rosettes of intricately branching, lacy-looking thalli, sometimes it's called the Rosette Lichen. Our Rosette Lichen atop its narrow ridge of deeply fissured Mesquite bark couldn't form its rosette.

Rosette Lichens are widely distributed in the Americas and Eurasia and are described as growing on trees in fairly open situations, which was precisely the case with ours.

*****

THE CANYON
On Google Earth the canyon of the Dry Frio River looks like a pale, crooked finger poking northward into a region of darkness. The dark area -- the Edwards Plateau -- is dark with hilly slopes mantled with evergreen Ashe Junipers and Texas Liveoaks. The canyon's floor is occupied with fenced-in pastures and a little dead-end road.

Wind inside the canyon normally is either warm Mexican air gushing northward, or cooler air flowing southward off the plateau. What a pleasure in late summer when hot, howling wind sweeps down the canyon making fast-moving silvery waves in big fields of tall grass.

It's hard to imagine how a piddling stream like the Dry Frio carved such a big canyon. However, here and there along the river huge boulders left in odd positions show that the canyon's formation hasn't been a calm, continual thing, but rather it's been roughly gouged out during very rare catastrophic flooding. A friend who studies pollen research for this area says that 10,000 years ago the climate here was much wetter, but 5000 years ago it was much drier.

Three or four miles south of here, in the 1980s, archeologists excavated a prehistoric campsite along the Dry Frio. Wandering bands of indigenous Americans had used the camp from about 7000 BC until historic times. During the late 1400s when the shipwrecked Cabeza de Vaca and a handful of followers passed near here they reported Pinyon Pines with wonderfully edible seeds, though now the pinyons are rare, only atop a few hills. Early indigenous groups were driven south by the Apaches, who later were attacked by the Comanche, and eventually all were displaced by European settlers.

Physiographers tell us that canyons can reach only a certain depth, not eroding below the current sea level. With time their walls decay, their troughs fill with sediment, and the whole landscape where the canyon used to be erodes to a fairly flat "peneplain" close to sea level. The peneplain exists until either the sea level changes or forces within the Earth raise the entire landscape so that the erosion cycle can begin again.

I relate to this canyon, for I know the feeling of coming out of nothingness, of slowly acquiring a history, a certain character, and a perspective on things. Moreover, like this canyon opening onto the low-lying Coastal Plain, nowadays I find I can cut no deeper into the meanings of things, and I experience a certain leveling out before a vast unknown ocean.

With this insight forming within, it's the Raven's raw croak echoing off the canyon's walls that sets me straight again, the unforeseen wildflower or moss making a surprise appearance along the trail that keeps me going, like the little stream of water trickling down the canyon's bottom, clear, sparkling, and filled with life, even after all that's passed.

*****

FEATURED ESSAYS FROM THE PAST:

"Awakening on LLano de Caballo" from the December 29, 2006 Newsletter, at http://www.backyardnature.net/n/p/061229.htm

"Black Cow, Foggy Dawn" from the July 13, 2006 Newsletter, at http://www.backyardnature.net/n/p/060713.htm

*****

Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.friocanyonnature.com/n/.