Issued from the valley of the Dry Frio River on the
southern slope of the Edwards Plateau, northern
Uvalde County, southwestern Texas, USA

July 28, 2013

The Dry Frio River Valley is a good place to see a fine selection of hawks. Michael Overton's "Birds of Uvalde County, Texas" lists 20 species under the heading "Kites, Hawks, Eagles & Allies," including such interesting ones as Swallow-tailed, White-tailed and Mississippi Kites, Common Black-Hawk, and Harris's, Short-tailed, White-tailed, Zone-tailed, and Ferruginous Hawks. Among those 20 species only two are noted as common throughout the year, and that's the Harris's and Red-tailed Hawks. I'm surprised to see the Harris's described as so common because in this valley I've not seen one. However, every day Red-tailed Hawks circle above us, often screaming their high-pitched, blood-curdling, snarling call from high up.

A few months ago my neighbor Phred drove upon an immature Red-tail feeding at the road's edge. The surprised hawk flew right into the path of Phred's car, despite efforts to avoid him. The hawk tumbled to the road's edge with a wing dragging the ground, unable to fly. After being bandaged up according to directions on the Internet he was provided a perch in a little greenhouse. Mindful of federal law prohibiting the keeping of bird predators, the hawk was free to fly through the greenhouse door whenever he wanted. However, with a drooped wing and free food every day, he stayed... until one morning he did fly out, sailing into the woods. He'd shown no signs of being able to fly, and his wing still seemed to drag, so this departure was unexpected. We've often wondered if any of the Red-tails always circling above the valley might be him. You can see a nice portrait of the bird, taken by Phred, at http://www.backyardnature.net/n/13/130728hl.jpg.

The plumages of immature hawks often differ drastically from the plumages of adults of their species, and at this time of year we see plenty of immatures. Therefore, it's worth learning the immature plumages.

For example, the other day a young hawk flew over the Center, as shown at http://www.backyardnature.net/n/13/130728hk.jpg.

Here the best bet is always that any circling hawk with broad, rounded wings and a fanned tail is a Red-tailed Hawk. However, this bird's tail not only is not reddish, but it bears faint, narrow bands.

Happily, patternings of dark spots on immature hawk bodies and wings are fairly consistent and predictable from species to species. On the bird in our picture, field mark to notice are the dark-tipped primary feathers at the wings' ends, an especially dark zone near the base of those primaries, the wings' white flight feathers having light barring, and the dark bar on the leading edge of the underwings.

These field marks inexorably lead us to the immature Red-tailed Hawk, BUTEO JAMAICENSIS, and so we learn that the tails of immature Red-tails when seen from below can indeed show faint, fine barring.


As I walked along the edge of a small pool in the mostly dry Dry Frio River, many dark, thumbnail-sized frogs jumped out of my way. One of them, instead of escaping into the water, hopped inland and took up position between two limestone cobbles as shown at http://www.backyardnature.net/n/13/130728fg.jpg.

I wasn't sure what species he was. My approach to identifying reptile and amphibian species is to visit the Herps of Texas website ("herps" refers to reptiles and amphibians grouped together) where all of Texas's herps are listed with thumbnail maps showing their distributions in Texas, as well as photos of the species. I go down the list looking at each picture of species the maps indicate might be found here in southwestern Texas. The "Herps of Texas" Frog Page is at http://www.herpsoftexas.org/view/frogs.

Using this approach I came upon the narrowly endemic Cliff Chirping Frog, found only in a few counties here in southwestern and central Texas. It's exceptionally small, like our subject in the picture, and when it escapes it finds a crevice in limestone rock into which to wedge itself, much like our frog sought to settle between two rocks. Also the heads of Cliff Chirping Frogs are unusually broad, like the head of ours. However, our frog was darker and the skin was rougher than on Cliff Chirping Frogs illustrated on the Internet, so I just wasn't sure.

On the Internet there's a very active Field Herp Forum attended by many serious herpers, at http://www.fieldherpforum.com/forum/.

I have an account there so I uploaded our picture and asked other herpers if they thought it was a Cliff Chirping Frog.

Within five minutes someone replied that it was a recently metamorphosed toad, not a Cliff Chirping Frog. Before long two others agreed. Our frog's skin is too rough and, as one herper said, "it just doesn't have the right gestalt," -- too stocky.

Well, we have several toad species here but, based on the fact that most toads I see are Coastal Plain Toads, and that that species displays bars on the hind legs like the tiny individual in my picture, I'm supposing that our picture shows a very young Coastal Plain Toad. In fact, maybe that bump at his lower back is what's left of his tail.

So, this is a very commonplace find, but it's worth relating the story to show that even commonly encountered organisms can challenge us, and that in figuring things out, you learn a lot, and have some fun.


Each morning I bike into the valley to water plants at the red cabin where I lived last winter. One job there is watering a row of ornamental sunflowers planted along a fence. This week a certain little black caterpillar species began eating the sunflowers' leaves, as shown at http://www.backyardnature.net/n/13/130728ct.jpg.

Volunteer identifier Bea in Ontario quickly pegged the caterpillar as that of the butterfly known as the Bordered Patch, Chlosyne lacinia. Bordered Patches are common here. Our "Butterflies of Uvalde County" picture of it resides at http://www.backyardnature.net/n/a/uvalde/005.jpg.

The "Butterflies and Moths of North America" webpage for this species describes the caterpillars as feeding on plants in the Composite or Sunflower Family, which among our wildflowers and weeds by far is the most represented of all plant families, so Bordered Patch butterflies should feel very much at home here, and are to be expected on sunflowers. In fact, another common name for the species is Sunflower Patch.

Bordered Patches are mostly a tropical and subtropical species, occurring from Argentina north through Mexico to southern California, casually to Colorado, Nebraska, and Kansas, and rarely even to western Missouri. Being found over such a large area, there's much variation in the caterpillar's appearance, from mostly orange with black spines, like ours, to black with a red-orange back stripe, to almost completely black. All variations have a red-orange head, though.

Neighbor Phred says that masses of little black caterpillars have been eating his sunflowers. I'm guessing that he has Bordered Patch caterpillars, for it's known that small, recently hatched Bordered Patch caterpillars are gregarious but when they grow larger they become solitary, like ours. I read that in southern Texas broods of Bordered Patch caterpillars may be produced throughout the year, and that during hot weather they may "aestivate," which is a state of reduced growth and development in response to heat and/or dryness, similar to winter hibernation.


Nowadays the little Dry Frio River consists of a chain of isolated pools separated by stretches of gravel. On the upstream side of each pool usually you find water flowing from the gravel, so the Dry Frio still flows, just mostly beneath gravel. All the ponds are shallow and many are choked with aquatic vegetation, such as the one shown at http://www.backyardnature.net/n/13/130728pw.jpg.

In that photo at the top, right, horizontal beds of Glen Rose Limestone outcrop, with water dripping from between some of the beds. At the top, left a thicket of Water-willow, Justicia americana, is stranded atop dry gravel, though earlier in the year the plants stood in water. What's especially interesting in the picture, though, is the aquatic vegetation. Note how slender little fingerlike items emerge from the water's surface, pointing at the sky. I've been waiting for this, for those fingers are the aquatic vegetation's flowering spikes. You can see them closer up emerging from tangles of floating leaves and stems at http://www.backyardnature.net/n/13/130728px.jpg.

A flowering, leafy stem lifted from the water appears at http://www.backyardnature.net/n/13/130728py.jpg.

We've run into this group of plants before, the pondweeds, genus POTAMOGETON, a monocot-type plant so distinct and specialized that it has its own family, the Pondweed Family, the Potamogetonaceae. We've seen the American Pondweed in Kentucky, and the Curled and Floating Pondweeds in Oregon. However, this Texas pondweed is different from those. About a hundred pondweed species are recognized, with 33 listed for North America, so it's not surprising to encounter a different species here.

The main field mark for this species is that its leaves are slender but with definite blades that don't crinkle, and the top leaves that float at the water's surface are attached to the stem by fairly short petioles. You might enjoy comparing our Dry Frio plant's leaves with the long-petioled ones of the Floating Pondweed we saw in Oregon at http://www.backyardnature.net/n/09/090614pr.jpg.

Our Dry Frio pondweed is POTAMOGETON ILLINOENSIS, mostly known as the Illinois Pondweed, though it occurs throughout North America, Mexico, Central America and South America. Sometimes it's also called Shining Pondweed. It's described as "a major submerged weed invading irrigation channels" in Argentina, and there are reports of it as an aquatic weed in Europe, so Illinois Pondweed seems to be a robust, adaptable plant.

Pondweeds are generally regarded as creating wonderful habitat for many kinds of small, aquatic organisms, and it's true that the water beneath our Illinois Pondweed's floating leaves teemed with tiny, pale specks darting about living their lives, plus there were mosquito fish and predatory aquatic beetles among them, so this "vegetation clogged pond" was a tremendously productive ecosystem.

Pondweed's drupaceous fruits (fleshy and not splitting at maturity, with one seed in a hard shell) are grainlike and stand about 1/8th inch tall (3mm) above the spike rachis, as shown at http://www.backyardnature.net/n/13/130728pz.jpg.

You can imagine that a duck might relish such a snack.


A year ago in Mississippi we looked at the abundant, yellow-flowered Composite or Daisy Family roadside weed known as Sneezeweed, shown at http://www.backyardnature.net/n/h/sneeze.htm.

Exactly one year after taking that picture, to the very day, here in Texas I photographed another yellow-flowered Composite with heads displaying the same unusual spherical "eye" as the Sneezeweed, though this one's eye was dark, not yellow like last year's Sneezeweed. This week's picture is at http://www.backyardnature.net/n/13/130728he.jpg.

A close-up of two flowering heads, the one on the left having had its flowers pollinated and is ray flower corollas discarded, is at http://www.backyardnature.net/n/13/130728hf.jpg.

A view of a flowering head with several disc flowers removed so you can see the egg-shaped receptacle upon which the disc flowers stand is at http://www.backyardnature.net/n/13/130728hg.jpg.

That picture also shows that between the closely packed disc flowers there are no papery bracts separating the cypsela-type fruits, and that the pappi atop the cypselae are low scales instead of the more usual white hairs.

These details -- especially the egg-shaped receptacle -- are the very same as for last summer's Sneezeweed in Mississippi. That's because our Texas plant also is a sneezeweed, which means that it's another species of the genus Helenium. It's HELENIUM ELEGANS, commonly called the Pretty or Elegant Sneezeweed.

Pretty Sneezeweed isn't weedy like last year's species, but rather prefers dry, rocky arroyo beds in limestone areas -- arroyos being streams remaining dry except after rains. Also, Pretty Sneezeweed's leaves aren't threadlike, like regular Sneezeweed's, and Pretty Sneezeweed doesn't occur over such a large area. It's found in arid northeastern Mexico, central and southern Texas, and here and there in Oklahoma, Arkansas and maybe Louisiana.

A worthy feature of Pretty Sneezeweed, besides its prettiness, is that it provides excellent nectar to native bees.

Sneezeweeds get their name from the earlier practice of drying leaves of one or another sneezeweed species to make snuff, which was then inhaled to cause a pleasurable bout of sneezing.


Arriving here last fall I found a fence-climbing vine displaying itself spectacularly. It was the Drummond's Clematis, CLEMATIS DRUMMONDII, whose masses of hairy-white fruiting heads showed up like refrigerator-size gobs of snowy white cotton rolled up against the fences being climbed, as shown at http://www.backyardnature.net/n/12/120902cl.jpg.

Nowadays the Drummond's Clematises, also known as Texas Virgin's Bowers, are flowering, and even in flower they present spectacles climbing the area's fences. You can see a small section of flowering vine back-lighted by morning sunlight at http://www.backyardnature.net/n/13/130728cl.jpg.

A flower close-up appears at http://www.backyardnature.net/n/13/130728cm.jpg.

Those are male flowers, for the flowers of Drummond's Clematis are unisexual, with different sexes borne on different plants. The picture shows many stamens composed of slender filaments tipped with small, baglike, pollen-producing anthers. Below the stamens arise white sepals -- segments of the calyx -- looking like petals, for there are no petals. You might enjoy comparing that male flower with a very different female blossom shown at http://www.backyardnature.net/n/12/120902co.jpg.

Once the female flowers are pollinated they drop their petal-like sepals and their styles elongate to form hairy "beaks," which give the flowers a surprising appearance, as shown at http://www.backyardnature.net/n/13/130728co.jpg.

When the beaks are a little hairier they start catching sunlight, shown at http://www.backyardnature.net/n/13/130728cp.jpg.

And then in a month or so the huge snowballs we saw last fall once again will appear in all their glory.

We have more than one clematis species here. To help you identify the Drummond's Clematis, our most common species, one of its distinctive compound leaves is shown at http://www.backyardnature.net/n/13/130728cn.jpg.


This spring my neighbor Phred gave me some sunflower seeds, suggesting that I plant them along the fence next to the red cabin. Now there's a pretty row of blossoming sunflowers along the fence, a pie-pan-size flowering head of which you can see at http://www.backyardnature.net/n/13/130728sf.jpg.

I've grown sunflowers before, but these surprised me. First, they're not the 10-ft-high (3m) giants I'm used to but rather most of them stand between waist and chest high. Also, several cultivar types are represented, including some blossoms that are dark, reddish-brown and others that are bright yellow. You might enjoy reviewing a page displaying various sunflower cultivars (thumbnails at page bottom) at http://rainyside.com/plant_gallery/annuals/Helianthus_annuus.html.

Most cultivated sunflowers derive from the wild HELIANTHUS ANNUUS, though 52 species are assigned to the Sunflower Genus Helianthus, and several of those species are cultivated. All sunflower species are native to North America and Mexico.

In fact, in the book Guns, Germs, and Steel, Jared Diamond asserts that most of the world's important cultivars are Eurasian in origin, with only a relatively few species native to the Americas, and most of those come from South and Central America, and Mexico. The single cultivar of importance worldwide originally from North America is the sunflower.

Though certain sunflower species produce edible tubers -- the Jerusalem artichoke, Helianthus tuberosus, is a sunflower -- it's the "seeds" for which early indigenous Americans domesticated the wild sunflower. The seeds are exceptionally good sources of calories, vitamin E, vitamin B1, magnesium, selenium and other nutrients.

Botanically, of course, sunflower "seeds" aren't seeds. Since sunflowers are members of the huge Composite, Sunflower or Daisy Family, what people call sunflower seeds are actually cypsela-type fruits -- meaning that the fruit is dry, doesn't split open at maturity, and contains just one seed. In our picture the yellow "petals" radiating from the flower-head's "eye" are ray flowers with flat corollas, while the "eye" is composed of hundreds of cylindrical disc flowers. In fact, on fairly mature heads it's easy to knock off the disc flower corollas to see developing "seeds" (cypsela-type fruits) as shown at http://www.backyardnature.net/n/13/130728sg.jpg.

At that picture's top, yellow-orange, cylindrical, disc-flower corollas stand beside one another with dark brown, pollen-daubed style branches from atop the maturing ovary (the future cypsela-type fruit) curling up from inside the corollas' throats. Below the disc-flower corollas the corollas have been removed to reveal maturing, enlarging fruits, or "sunflower seeds." The white, circular items in the center of each fruit are scars left by the disc corollas. On one side of each fruit arises a dark brown, slender, sharp-pointed scale. These are receptacle bracts of the kind we've seen in many Composite Family wildflower heads.

An interesting close-up of the tops of some disc flower corollas is at http://www.backyardnature.net/n/13/130728sh.jpg.

There you see fuzzy, curved style branches dusted with yellow pollen and arising from dark cylinders formed by each flower's five anthers fusing together at their margins. The anthers in turn arise from the center of the disk corollas, each corolla topped with five sharp-pointed lobes, which are analogous to a larger flower's five corolla lobes or petals.

Maybe you noticed in the above picture of a pondweed steam just removed from the Dry Frio (http://www.backyardnature.net/n/13/130728py.jpg) that on my lower finger there's light brown, crusty material. That material is marl, and the pondweed's lower leaves and stems were covered with it. You can still see some on the plant.

An even more graphic display of brownish marl coating submerged vegetation can be seen in our picture of the network of leaves and stems of flowering bladderworts we looked at a while back at http://www.backyardnature.net/n/12/121104uu.jpg.

In that picture, mostly you see marl, not only coating all submerged parts of the bladderwort but also the rocks and mud below the bladderwort. In fact, most -- nearly all -- of the Dry Frio's submerged bed is thickly coated with marl, as you can see in a typical shot through ankle-deep water at http://www.backyardnature.net/n/13/130728mr.jpg.

When water goes down, the marl dries into a gray-brown coating on all rocks and exposed vegetation, which gets washed off with subsequent rains. The presence of marl profoundly affects the Dry Frio's aquatic ecology, mainly because it's composed of stable minerals in which the elements are "locked up" -- unavailable to organisms.

My first encounter with marl was in geology class, when I learned that the mud accumulating on ocean floors -- mud rich in calcium carbonate and microscopic mineral particles -- was marl. Marl that gets buried for millions of years under high pressure eventually hardens to limestone, which is mostly calcium carbonate. When the calcium carbonate dissolves in rainwater, precipitates from the water, mingles with microscopic minerals of various kinds, and settles to the water body floor, once again it's marl.

Water holding high concentrations of calcium carbonate is somewhat alkaline. Under such chemical conditions, phosphorus in the water also is precipitated in the form of various insoluble compounds and becomes unavailable to algae and other phytoplankton. Phosphorus is one of the most important macronutrients for green plants, so the water's alkalinity in a way "starves" algae and other aquatic plants.

Because the stream floor consists mostly of constantly accumulating marl there's relatively little organic matter on the floor, which generally serves as the base of ecological pyramids. Microbes break down the organic matter, larger organisms feed on the microbes, and still larger organisms feed on those, and on up the pyramid. But, without much organic matter, there can't be much of a pyramid. In general, aquatic habitats in which marl smoothers the floor are regarded as "oligotrophic" -- meaning that despite plenty of oxygen being available, a lack of plant nutrients results in a sparse growth of algae and other organisms. Oligotrophic water may be exceptionally clear and "clean-looking."

That doesn't necessarily mean that marl-bottomed bodies of water are ecological deserts. Nutrients and oxygen are present -- just that they're covered with marl. Certain aquatic plants may be able to get their roots below the marl, into a nutrient-rich environment. In this Newsletter you've seen what a robust community of pondweed has rooted in a pool with lots of marl. Maybe you also remember last December's watermilfoil, shown in very clear water in a Dry Frio pool at http://www.backyardnature.net/n/12/121021my.jpg.

Where such robust growth takes place, some stems and leaves always are dying and contributing to organic matter on the floor, which then can serve as the basis of an ecological pyramid -- if other organisms can get to it before it's smoothered in marl.

In fact, the ecology of marl-rich streams like the Dry Frio is very complex and depends on many local variables. Marl is natural and certainly has been present in the Dry Frio River ever since it began issuing from the Edwards Plateau, which is basically a big tableland of limestone composed mostly of calcium carbonate. Therefore, one can assume that the organisms in the Dry Frio over millions of years have evolved exquisite adaptations to their environment, and that the community hosts the organisms it needs most.

Still, I began wondering about the Dry Frio's marl when beneath the microscope I first examined mud and the surfaces of submerged rocks from the river, and found surprisingly little life. The microscopic organisms I've profiled from the river predominantly were found on and in aquatic plants, or free-ranging in the water, but not in the marly mud or on marl-coated rocks.



"Thoughts on a David Orr Essay," from the May 5, 2007 Newsletter, at http://www.backyardnature.net/n/p/070505.htm

"Thoughts on Cleansing Oneself" from the November 22, 2009 Newsletter, at http://www.backyardnature.net/n/p/091122.htm


Best wishes to all Newsletter readers,


All previous Newsletters are archived at http://www.backyardnature.net/n/.