November 18, 2012

AXIS DEER
Nearly on a daily basis people living in the valley of the Dry Frio River see pretty gatherings such as the one shown at https://www.backyardnature.net/n/12/121118ax.jpg.

That's part of a herd of about a dozen Axis Deer, AXIS AXIS, next to the road to the house I'm painting. Here Axis Deer are not as commonly seen as White-tailed ones, but they are still very common. Within five minutes of walking of where I am now, I'll bet there at least 20, and within a radius of a half-hour walk, surely a hundred. Especially you see their flocks moving at dusk. Sometimes, I've been told, hundreds gather at dusk in the Big Bluestem grass pastures along the entrance road.

Even from a distance it's easy to distinguish native White-tailed Deer from the Axis because adult Axis Deer are covered with white spots, while White-tailed adults are plain brown, with only the fawns being spotted. Even old Axis males with very large antlers are heavily spotted.

Another difference is that Axis Deer are noisy. A White-tailed Deer can sound a fairly lusty snort or whistle, but these Axis Deer can be heard from a long way off. With a little practice you can distinguish the harsh yelp of the female from the even harsher, somebody-being-murdered bellow of the male. You can hear one of several Axis calls in a YouTube video at www.youtube.com/watch?v=fYXztketKJo.

Axis Deer are native to India and parts of adjacent countries. They were introduced into Texas in 1932. A study in 1988 found self- sustaining herds in 27 counties in central and southern Texas, with the highest population density here on the Edwards Plateau.

When you ask the local folks about the wisdom of having this imported species roaming around, sometimes they assure you that Axis Deer have different eating habits from the native White-tailed Deer, and therefore are no threat to them. However, the Institute for the Study of Invasive Species, a member of the Texas State University System, states that "Axis deer are known to occupy the same ecological niche as whitetail deer. This means they compete with whitetail deer for available resources. With an increased resistance to native diseases, axis deer are not susceptible to the same population decreases resulting from local disease outbreak. This would allow the axis deer populations to grow out of control, while the whitetail deer suffer from local disease outbreaks."

Still, most people around here like their Axis Deer. Since the Axis is an invasive species, normally they can be hunted year round, and the hunter can kill all he or she wants. People seem to agree that Axis flesh tastes much better than that of White-tailed Deer. Most land in this area is owned by large landowners who often sell hunting rights to outsiders. Having Axis Deer is a big attraction to many hunters, so usually the Axis are welcomed.

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SNOUT BUTTERFLIES
Following the trail down to the little Dry Frio River behind the cabin suddenly I realized I was inside a cloud of butterflies. They were all over and in and out of a Netleaf Hackberry tree, still prettily bearing this year's crop of sweet but big-seeded red fruits, and nowhere else. I couldn't see that the butterflies were doing anything there such as laying eggs. They seemed to just like flitting in and out of that tree.

The butterfly species mobbing the hackberry was one of our easiest to identify because of what appears to be its very long, pointy head. You can see one at https://www.backyardnature.net/n/12/121118sb.jpg.

That's an American Snout, LIBYTHEANA CARINENTA, distributed from Argentina north through Mexico and the Caribbean area into all of the southern US, from central California, Colorado and most of the eastern US. And it makes sense for American Snouts to be congregating in a hackberry tree on a sunny afternoon in mid November in southwestern Texas, for the species' caterpillars feed on various hackberry species -- species of the genus Celtis. My cloud of Snouts must have been making babies there when I wasn't looking.

What looks like a pointy head or a snout on the butterfly actually are unusually large and extended "labial palps," which are mustache-like mouthparts covered with sensory hairs and scales. Other butterfly species have labial palps, too, just not so conspicuous. For example, you can see the labial palps on a Gulf Fritillary at https://www.backyardnature.net/n/12/121118sc.jpg.

In that picture the coiled, dark brown thing at the bottom is the strawlike proboscis through which nectar is drunk. The large, brown, spherical item above it is one of the butterfly's compound eyes, and the two black, slender items at the picture's top, right are antennae. The mostly white, fuzzy part at the picture's bottom, right is one of the labial palps. There's another palp on the other side of the butterfly's head. The palps' hairs are sensitive to touch and other stimuli. Basically they help the insect figure out what's good food and what's not.

These enormous labial palps help define the Snout Butterfly Subfamily, the Libytheinae, consisting of two genera and about ten species. Our American Snout is the only member of the family found in North America.

Upon my arrival here I was told of occasional mass migrations of this species, whole clouds of them so thick that if you're driving through them you have to constantly stop to wipe off your windshield. This fall I've seen only one movement of the species that looked like a migration, but it wasn't really cloudlike -- just many widely spaced Snout Butterflies all flying the same direction.

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LAWNFLOWER
Nowadays in the weedy grassy area around the cabin there's a small, sprawling herb with tiny yellow blossoms only about 5/16ths inch across (8mm). It's a member of the Composite or Daisy Family, so what look like petals are actually ray flowers. Normally ray flowers are fairly evenly distributed around a composite blossom's perimeter, but these flower heads are so small and the ray flowers so few that often they look randomly placed, giving the little blossom a haphazard appearance. You can see all this at https://www.backyardnature.net/n/12/121118lf.jpg.

Once the flowers are pollinated, as is normal for composite flowers, the corollas fall off, the remaining seed-like, dry, one-seeded fruit (a cypsela) expands, and the scaly pappus atop the cypsela also expands to form become a crown of spiny "awns" atop the cypselae, which typically aid in fruit dispersal. These upward projecting spines atop some cypselae are shown https://www.backyardnature.net/n/12/121118lg.jpg.

You probably noticed that this is a hairy little plant. Just for the fun of it I photographed some hairs on the bottom of a leaf, as shown at https://www.backyardnature.net/n/12/121118lh.jpg.

Around here this is a very common, weedy herb in lawns and along roads and trails. It's a native American species, found from South American north through Central America and Mexico into the US Deep South. This native American species, however, has "gone weedy" in many warm, moist countries. Despite being so common and widespread it has no English name most people have settled on. My Field Guide to Southwestern and Texas Wildflowers calls it Lawnflower, but elsewhere it's called Straggler Daisy, Sprawling Horseweed, Horseherb and other names. It's CALYPTOCARPUS VIALIS.

This little herb attracts small butterflies like sulfurs and skippers. Altogether it's a fine little plant, its yellow blossoms very pretty in the dark-green grass that at this time of year with sunlight's intense light and shadows, esthetically, seems "just right."

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"BALL MOSSES" FRUITING
In Mexico we saw lots of bromeliads -- those epiphytes (plants living on other plants but not necessarily parasitizing them) that form such a beautiful and interesting element of tropical American vegetation, often creating veritable airborne gardens on the limbs of larger trees. In the Temperate Zone, bromeliads are often cultivated as potted plants, but few species can handle cold weather. One bromeliad that makes it as far north as the US Deep South is Spanish Moss, which is an unusual bromeliad not only because it can stand some freezing, but also because it forms dangling strands of connected plants. The vast majority of bromeliads are tufted plants looking like individual small agaves. Bromeliads are such a unique group of plants that they have their own Bromeliad Family, the Bromeliaceae, harboring over 3000 species.

Spanish Moss occurs in Eastern Texas, but here in the southwestern part it's too arid for it. A few miles south of here someone has strung Spanish Moss in their trees, and it's survived there for several years, but it hasn't spread to other trees, and I've never seen it on other trees in the region.

However, we do have another native bromeliad species here and it's abundant. People call it "Ball Moss," which is unfortunate because mosses reproduce by spores while bromeliads are flowering plants. Ball Moss is TILLANDSIA RECURVATA, a member of the same genus as Spanish Moss, Tillandsia usneoides. These two relatively cold-tolerant species are very closely related. You can see one of our typical Ball Mosses on a tree's dead branch near the cabin at https://www.backyardnature.net/n/12/121118ti.jpg.

We've run into this bromeliad before. In arid north-central Mexico, in Querétaro, we often saw it growing thickly on power lines, as shown at https://www.backyardnature.net/q/ballmoss.jpg.

Ball Moss occurs in South America up through Central America, the Caribbean and Mexico, into the US states of Arizona, Texas, Louisiana and Georgia.

Nowadays our Ball Mosses are fruiting. In the above picture the slender stems arching from the tuft of plants bear cylindrical capsules that are splitting open now, releasing seeds. The seeds are equipped with long hairs to help with wind dissemination. You can see a split-open capsule with its fuzzy contents, with slender brown seeds at the top of several tufts, at https://www.backyardnature.net/n/12/121118tj.jpg.

I was curious as to what Ball Moss's gray, crusty surface might look at high magnification, so I looked with our dissecting scope, and you can see what I saw at https://www.backyardnature.net/n/12/121118th.jpg.

Ball Moss's surface is well protected by an armor of silvery, overlapping scales. This may help explain the species' relative tolerance of cold weather.

In a recent Newsletter I mentioned that many landowners in this area despise one of the two dominant natural trees here, the Ashe Juniper, believing that it's an invasive that sucks water from the ground. Many landowners uproot and burn as many Ashe Junipers as they can, often at great expense, feeling that they are providing a public service. I've addressed the situation on our Ashe Juniper page at https://www.backyardnature.net/n/w/ashe-jun.htm.

A similar situation exists with regard to Ball Moss. In minds of many property owners here, if you have trees full of Ball Moss, you're negligent in controlling an awful pest that's killing our shade trees. They say you need to spray your trees to kill the Ball Moss. Often Kocide 101, a fungicide, is recommended for "infestations," but around here most people just spray a mixture of water and baking soda.

The reason people don't like Ball Moss is because often they see what's shown at https://www.backyardnature.net/n/12/121118tk.jpg.

That picture shows an Ashe Juniper with healthy, green foliage on the left, which is Ball Moss free, while on the right the dead branch is absolutely choked with Ball Moss. Therefore, Ball Moss killed the branch.

The other way of looking at it is that in this droughty area large tree branches are always dying back when the rains fail, as they have been lately. The dead branches devoid of leaves provide a perfect habitat for Ball Moss, which moves in quickly and aggressively.

Large colonies of Ball Moss do shade a tree's lower branches but if the Ball-Moss-filled branch bore the tree's own foliage, the shade wouldn't be much more. Ball Moss does sometimes encrust a stem so thickly that new tree shoots hardly have a place to form. However, Ball Moss "infestations" occur on weak, dying or dead branches, so there's not much competition there between sprouts and bromeliads.

Whatever the reasoning, the people I've spoken with just won't believe that Ball Moss is anything but an ugly pest needing to be exterminated or at least "cleaned" from trees around the house.

When I was student we learned that bromeliads neither hurt nor help the trees they populate. However, now it's clear that they do contribute to the environment they occupy, like all natural organisms. A 1994 study in the Canadian Journal of Botany {72 (3): 406–8} found that our very own Ball Moss harbors the nitrogen-fixing bacterium Pseudomonas stutzeri. Ball Moss helps the tree it's living on by converting nitrogen in the air, which is unusable to flowering plants, into a usable nitrogenous compound the plant can't live without. When Ball Mosses fall onto the ground, which they do constantly, they're "fertilizing" the soil around their host tree with a nitrogenous, organic substance -- their own bodies.

So, droughts weaken our local trees, causing certain branches to die. Mother Nature sends in Her first responders, Ball Moss, whose job it is to fertilize the tree with nitrogen. But people wanting to help their trees kill the Ball Moss.

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POND SCUM
It's been awhile since it rained here so large cracks are opening in the ground, and the little Dry Frio River is down to just a trickle, in some places disappearing altogether as its waters seep downstream beneath gravel bars and fields of cobbles. Here and there pools have formed, like little ponds, and lately I've been noticing a certain scum gathering in bunches atop the water. You can see what I mean at https://www.backyardnature.net/n/12/121118ag.jpg.

Up close you see that very fine, hairlike filaments -- which from the first I assumed to be a kind of alga -- arise from the underwater stems of aquatic plants. The scum atop the water is mostly composed of bubbles, which one guesses to be filled with the oxygen the filaments photosynthesize during the day. You can see the submerged, hairlike, reddish filaments beneath some floating scum at https://www.backyardnature.net/n/12/121118ah.jpg.

We have a microscope here so I wondered if I could identify what kind of alga this was. A couple of filaments under high magnification are shown at https://www.backyardnature.net/n/12/121118ai.jpg.

I couldn't match our photograph with anything found on the Internet by doing an image search on the keywords "filamentous alga species." However, some features we can see very clearly narrow down the possibilities considerably.

First, our specimen is indeed filamentous. Many alga species live as freely floating single cells, or their cells are connected in some manner other than end-to-end like ours, forming a filament.

Second, our filament is non-branching, while certain other common types are highly branched.

Finally, you can see that the cells are shorter than they are broad. It's much more typical for the cells of filamentous algae to be considerably longer than broad, so this is a good field mark.

The only genus of filamentous algae I could find with these features is one sometimes called Hair Alga, genus ULOTHRIX. Ulothrix is one of the more common filamentous algae in ponds, streams and rivers, and it's easy to find pictures of it forming scum, just like ours. However, none of the species I saw had cellular structure exactly like ours, plus all references I found to Ulothrix indicated that it is bright green. You have seen that our scum-maker definitely shows a reddish hue.

After a great deal of Internetting, comparing pictures, and learning how outdated much of my understanding about the world of algae and algae-like things is, I've come to these understandings about our scum:

Probably the thing we're seeing used to be thought of as an alga -- one of the blue-green group -- but now it's classified as a Cyanobacterium. There's a good chance that it the genus Oscillatoria. It's been hard for me to think of bacteria as producing alga-like filaments easily visible with the eye, but that seems to be the reality of things.

To give you an idea of how poorly understood yet how important this group of organisms is, consider this: The tiny marine cyanobacterium Prochlorococcus was discovered only in 1986, yet it accounts for more than half of the photosynthesis that takes place in the open ocean. And scientists believe that the ocean's phytoplankton contribute between 50 to 85 percent of the oxygen in Earth's total atmosphere. Therefore, a very substantial part of the oxygen you and I are breathing right now has been provided to us by cyanobacteria.

Praise be to the producer of those little bubbles in the scum down on the surface of the Dry Frio River behind the cabin.

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LIMESTONE CAPPED HILLS, SEA URCHINS ON VALLEY FLOOR...
The valley of the little Dry Frio River in which I live runs northward, cutting into the Edwards Plateau. As you travel up the valley, often you see massive white limestone outcrops at the tops of hills, as shown at https://www.backyardnature.net/n/12/121118g1.jpg.

The hill isn't as high as it might seem, because vegetation covering it is low and scrubby. If a person were standing at the cliff's edge you'd see that the cliff is only about 150 feet (45m) above the valley floor.

One reason that limestone-capped hills interest me is that back in geology class I was taught that in the humid eastern US normally hills are capped with sandstone, but in the arid West, often it's limestone. That's because rainfall is slightly acidic and over time dissolves limestone, which is calcium carbonate, a mineral of which one property is that it dissolves in acid. Since hills in general are capped with erosion-resistant rock, the East's water-weakened limestone in not nearly as resistant as sandstone, so a normal Eastern hill, if capped by anything, is capped with sandstone. But out here where rainfall hasn't decayed the limestone to the extent it has in the East, it's pretty hard rock, and it caps lots of hills, like the one in the picture, and like many places in arid northern Mexico.

Another reason this outcropping limestone is interesting is that here we're at the southern boundary of the Edwards Plateau, and the Edwards Plateau is known to be mostly composed of limestone of Cretaceous age. The limestone outcropping in our picture is that limestone. Geologists have figured out that it was deposited at the bottom of a vast inland sea that during Cretaceous times, about 70 million years ago, cut across present-day Texas and much of central North America. At that time dinosaurs ruled the Earth, but you won't find dinosaur footprints in our hilltop limestone because the stone was deposited in the bottom of that sea, where dinosaurs didn't roam. "Forces from within the Earth" have lifted the former ocean floor to where it is atop our hills today.

Also I've been fascinated by the jumbles of loose material exposed in cliff faces at the edges of our little Dry Frio, as shown at https://www.backyardnature.net/n/12/121118g2.jpg.

In that picture, it's easy to walk up to the cliff face and with your fingers dislodge any of the cobbles you see protruding the face, which is composed of sand, silt and other loose material. The size of the cobbles shows that the water that left them there was running very fast. And look at that rock "floor" just above the grass at the river's edge. That's shale rock. It's weak shale, easy to scrape apart with a knife, but not soft enough to call mudstone.

That jumble of sand, cobbles and boulders looks as if it were deposited fairly recently -- maybe only a few thousand years ago. And, maybe it was. Maybe the Dry Frio eroded the valley down through the Edwards Plateau's limestone to that bed of shale, then partially filled the valley back up with sand, cobbles and boulders, and now is cutting back into its former depositions.

But, that bed of shale hasn't been deposited there recently. I'm sure of that not only because of logic but because of what I found while studying thebed this week. You can see my discovery at https://www.backyardnature.net/n/12/121118g4.jpg.

That's a globe-shaped fossil I pried from the shale with my fingernails. It's about half an inch across (12mm) and looks very much like the sea urchin shells found so often along the beach down in the Yucatan.

Best I can tell with my little Golden Nature Guide to Fossils, it's the genus CIDARIS, sometimes known as the pencil sea urchins. The genus arose well before the Cretaceous, and continues living in the world's shallow marine environments. The interesting word in that description of Cidaris is "marine." Like the limestone capping our hills, this bed of shale was deposited in the ocean back in Cretaceous times, when dinosaurs roamed the Earth.

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THE EDWARDS PLATEAU ON GOOGLE EARTH
The Edwards Plateau is the southernmost extension of North America's Great Plains. If you've been across North America's Great Plains you know that it amounts to very much flat, somewhat elevated land. Physiographically, the Edwards Plateau is distinguished from the rest of the Great Plains precisely because it is not almost entirely flat upland. The Edwards Plateau is hilly. It's hilly because the entire plateau is tilted enough for water to rush off it, eroding as it goes, forming hills and valleys. The northern and western parts of the Edwards Plateau can range from being somewhat flat to undulating, but here on the southern (and eastern) boundaries the topography is rugged, consisting of canyons separated by flat or undulating divides. These much-dissected southern and eastern parts are known as the Texas Hill Country. I've prepared a Google Earth view to orient us at https://www.backyardnature.net/n/12/121118g3.jpg.

Notice the dark region occupying the area west of Austin, north of San Antonio, and extending westward to the Mexican border -- most of the picture's upper left and upper center. The dark area is the Edwards Plateau. I'm guessing that the dark areas in the picture represent mostly the Plateau's Ashe Junipers. The Mexican border is that yellow line at the picture's lower, left. The big lake across which the border cuts is Amistad Reservoir at Del Rio.

Notice that here at the Plateau's southern boundary the transition to the Coastal Plain is not in the least a well defined front. Everywhere it is cut by streams flowing from north to south. Do you see the white dot with a yellow arrow pointing to it? That's where our pictures are taken, where these words are being written.

The paler land to the south and east of San Antonio is mostly the landscape of the fairly flat and younger Coastal Plain Province.

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FEATURED ESSAYS FROM THE PAST:

"Not Saying Anything," from the December 6, 2009 Newsletter, at https://www.backyardnature.net/n/p/091206.htm

"On Not Saying Anything" from the September 11, 2011 Newsletter, at https://www.backyardnature.net/n/p/110911.htm
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Best wishes to all Newsletter readers,

Jim

Visit Jim's backyard nature site at https://www.backyardnature.net