Tag: velvet mesquite bosque

A Thousand Songs Under the Cover of Darkness, Floods Transform the Land, and the Wonderful Creatures of October

Darkness settles over the land. Many miles from the lights and sounds of towns and cities, Arizona’s Middle San Pedro Valley sprawls wild and still. At twilight, only a faint poorwill and a pair of great horned owls can be heard. The coyote telegraph erupts and then fades as it travels from ridge to distant ridge. In contrast to the rich variety of summer  sounds, an autumnal hush blankets the countryside.

At day’s end, dusk gently ebbs into darkness as a brilliant October moon emerges from the far shores of the eastern horizon. Here, in our mesquite bosque, the peace and comfort of the night suddenly give rise to a thousand voices raised in the jubilance of courtship. These are sweet, almost melodic sounds – October’s distinctive nocturnal biophony. Tree crickets are singing from the ancient trees, thousands of them spread across the valley floor, their songs a vivid proclamation of thriving life within an otherwise quiet forest.

This species of tree cricket sings from the tall mesquites in our bosque. Its ecology is intimately connected to velvet mesquite trees. These are small insects with a big voice.

I have come to love the sounds of these delicate, gossamer-winged insects. Long after summer’s insect frenzy, when most species have faded from the scene, tree crickets come to life in the coolness of October nights. The males raise their transparent wings, then call to the females by stridulating – in other words, they rub certain parts of their bodies together to produce a surprising volume of sound.  Females are drawn to these love songs. The males go one step farther by offering their mates a special  reward. After mating, metanotal glands located on the dorsal side of the male’s abdomen secrete a substance that the female feeds on.

Eight species of tree crickets inhabit southeastern Arizona, where they produce two generations each year. The ones singing in local October bosques belong to the genus Oecanthus. Each species has its own unique song. However, even among the same species, sound can vary quite a bit depending upon air temperature. The frequency (or pitch) of the crickets’ songs increases as temperatures rise and slows as temperatures fall.

A bizarre butterfly landed on my screen door last week – an American snout butterfly, Libytheana carinenta. Last year, large numbers of these butterflies erupted all over the valley in late summer. Snout butterflies use their strange shape to blend in with their surroundings. When perched on a plant stem, their elongated “snout” breaks up the outline of their bodies, resembling a broken twig or a thorn. The range of snout butterflies extends all the way to South America. They are known for migrating across landscapes in huge aggregations. 

A study in camouflage, the American snout butterfly sports wings that blend well with tree bark and a unique body shape that helps to conceal the insect when at rest.

This summer’s plentiful monsoon rains have continued well into October. Since the monsoon began on June 18, our rain gauge has recorded an amazing 13.46 inches of life-giving rainfall. 

One of the local washes experienced some large summer floods. I took a walk down this wash with a friend a few weeks ago, to have a look at the powerful changes wrought upon the land by the big floods. What we saw was in stark contrast to the wash I had known from walks during the past several years.

During recent times, this broad wash had been covered by a wall-to-wall effusion of burro bush (Hymenoclea) standing six or more feet tall with a galaxy of roots anchoring the bushes to the ground. The flood had erased most of that growth, leaving behind a clear streambed lined with heaps of debris – tree trunks, plant material, rocks, and more. The floor of the big wash had been totally rearranged, its topography and course markedly changed during a couple of events that lasted only days.

In places where floodwaters form swirling, circular eddies, holes are dug into the wash floor like this one. These depressions can be very large and quite deep. They often hold pools of surface water that can last for months after flooding, a valuable offering to birds, mammals, and other wild creatures in this desert ecosystem.

Powerful floods like these transport thousands of tons of boulders, rocks, gravel, sand, clay, and a wide variety of organic materials – whole trees, cacti, and other plants.  Downstream, entire soil profiles are altered and built as sediments settle from the turbid waters. Cutbanks collapse, dropping great layers of soil into the roiling floodwaters, releasing seeds that have lain dormant from ancient times into the present-day   ecosystem. Old genetics from times long gone may invigorate plant populations and enhance the genetic variability – and hence, the viability – of modern plant communities.

Most people would simply label this collapse of a stream-side cutbank as “erosion.” That is an accurate use of the word, but I see much more going on here.

Debris piles left along the stream banks can be very large, consisting primarily of tangled, broken bushes, parts of trees, and other plant matter. They provide shelter and denning sites for small mammals, reptiles, amphibians, and other creatures. Floods are not all bad – they are simply a natural, intrinsic agent of change, some of it beneficial, some not. People often label floods as “bad,” but that viewpoint roots in anthropocentric thinking, a myopic way to  view our world.

The ecology of many native species of plants and animals actually depends upon flood events. The beautiful stands of cottonwoods that line the San Pedro River could not exist were it not for floods creating the specific conditions that their seeds require for germination. The riparian forests that accompany the river depend upon having their roots tap into  subsurface aquifers. The aquifers get recharged when floods happen.

As floodwaters recede, the bed of the San Pedro River leaves records of local wildlife in the drying mud. Here, the patterning of fine surface cracks results from a place where the river water subsided very gradually with little or no turbulence, resulting in the deposition of extremely fine clay particles. As these clay deposits dry, they crack in characteristic patterns.

October typically brings us the last ophidian visitors of the year, most of them not to be seen until next spring. A beautiful gopher snake was here last week, and as I write this, a diamondback is curled up a short ways from my entry door.

An October gopher snake, crawling along the wall of one of our buildings. This one was a male, measuring right around 63 inches in length. Always welcome here, as are all snakes.

The year’s last generation of pipevine swallowtail butterflies occurs in October. I found this gorgeous caterpillar recently – it is either in the fourth or fifth (last) instar of its development, after which it will climb a plant stem and metamorphose into a chrysalis suspended by a single loop of silk as it waits out the winter season. The leaves visible in this image are pipevine leaves, (Aristolochia), the only plant that these caterpillars feed upon.

October is THE month for seeing pinacate beetles (Eleodes spp.) – they are literally everywhere at this time of year, easily noticed because of their large size, slow movements, and diurnal habits. When they feel threatened, pinacate beetles stop moving and assume this head-stand posture. If the threat escalates, (for example, when a bird tries to grab the beetle), the beetles fire a noxious, very disagreeable fluid from the tip of their erected abdomen. Chemical defenses are very common among many insect species.

Just a few days ago, I noticed this small tuft of feathers laying on the ground. Immediately, I began searching the area for more, because such a find usually indicates that a bird was recently preyed upon somewhere nearby.

I soon found many feathers like this, their shafts intact. Intact shafts indicate feathers that were pulled out, not bitten and yanked out as mammals do. So this was the work of a predatory bird, likely a Cooper’s hawk that I have been seeing frequently of late. This was a special find, for these feathers could have come from only one species, a gilded flicker. Gilded flickers are relatively rare in local bosque habitats.

An Astonishing Eruption of Beetles, a Rare Visitor, and Bosque Lushness

There has been a sudden and tremendous eruption of small beetles in the local mesquite bosque. A dense, tall understory of pigweed, (Amaranthus palmeri) covers the floor of the woodland, an exuberant growth enabled by recent monsoon rainfall. When I walked into these plants this morning, curtains of tiny beetles took flight  from the pigweed at my every step, thousands upon thousands rising upward like a reverse blizzard.  

The leaves of the pigweed plants had become dotted with countless small holes during the last two days. This morning, the plants revealed that an orgy of feeding had taken place during the night. Literally all of their leaves had been reduced to a ghostly remnant of reticulated veins with no leaf tissue left in between. Every plant, everywhere I looked – consumed overnight.

Acres and acres of bosque understory were fed upon by an almost inconceivable number of small insects. The plants looked almost shredded.

A pigweed leaf after the night’s heavy feeding spree.

Naturally, I had to know what these beetles were. They were diminutive, measuring around 4-5mm in length. Up close, the beetles were beautiful, sporting brightly colored, broad white bands running lengthwise across their shiny black elytra. After some research, I learned that they were known as “pigweed flea beetles,” Disonycha glabrata. Their ecology entails a close relationship with specific host plants – they will feed only on plants in the genus Amaranth. I have witnessed dense growths of pigweed during most of my summers here; I had noticed these beetles in prior years, but never in such spectacular abundance. Why had their population so suddenly rocketed this year? I can only guess. Perhaps this year’s rains were perfectly timed at just the right intervals and in perfect amounts to encourage such an event? Maybe it has something to do with their predators…or  some other mechanism?

A pigweed flea beetle, Disonycha glabrata.

When insects erupt in large numbers, people are often quick to react with alarm and negative attitudes. Yes, they shredded an entire forest understory – but was that a bad thing? Or simply natural change? It is not our place to pass judgement on what happens in the natural world. Both the beetles and their host plants are native constituents of this ecosystem. So, I do not necessarily think that what has happened is somehow wrong or alarming, but it is interesting.

I found another creature wandering in the pigweed last week – a young adult Sonoran Desert Tortoise! We see these reptiles rarely here in the bosque; they are more partial to nearby upland desert habitat types. This one’s carapace was between 9 – 10 inches long, and like most of its kind, it was cautious, slow-moving, and appeared unfazed by my presence.

The Sonoran Desert Tortoise that I discovered resting peacefully under the trees. This reptile and its close relatives have recently undergone taxonomic revision – to scientists, it is currently known as Gopherus morafkai.

The tortoise’s powerful front legs are clad in rows of thick, hard scales that assist in digging and may help the turtle resist serious injury from predators. When threatened, the tortoise tucks its head in and then covers its front with these remarkably well-armored legs.

A few days ago, I went out on a walk with a naturalist-friend. He shared a special area with me, a mature mesquite bosque with a remarkably rich, lush understory. I was deeply touched by the feel and presence of this almost subtropical woodland. The image below provides some insight into the kind of verdant growth that this “desert” valley is capable of hosting.

A jungle-like wall of vining plants drapes over young trees and shrubs in one of the most lush, beautiful velvet mesquite bosques I have ever seen. Just beyond the reach of this image was a barbed-wire fenceline. On the far side of the fence, cattle grazed – the ground under that part of the forest had been virtually wiped clean, transformed into a deeply impoverished world with respect to native plants and wildlife. Mesquite bosques as rich and fecund as this one have become very rare – cattle are commonplace. How is this right?

Living Jewels that Seek Fire and Eat Wood

Among the most important components that power the machinery of forest life are insects – beetles in particular play crucial ecological roles in forests.  One of the largest beetle families is the Buprestidae, represented by nearly 16,000 species. These creatures are known as “jewel beetles” due to their family’s spectacular array of iridescent colors and patterns. The insect pictured above is one dazzling example, native to the coniferous forests of the Rocky Mountains.

One of the world’s largest jewel beetles is Euchroma gigantea, native to Amazonia. These insects can measure over two inches in length. This is a mounted specimen from Brazil, part of the author’s collection.

In most living organisms, iridescence is enabled by pigmentation. Jewel beetles are different – their iridescence is structural in origin; microscopic texturing on the surfaces of their exoskeletons selectively reflects specific frequencies of light while absorbing others.

Most jewel beetles lay their eggs on dead or dying trees. Once the eggs hatch, the beetle larvae go to work, chewing their way through the wood. They leave a maze of tunnels in their wake. Some species of jewel beetles will lay their eggs only on freshly burned trees. These specialized insects are known as pyrophiles (literally, “fire loving”). Forest fires create a nearly instant Shagri-la for them.

The larvae (or grub) of a jewel beetle found inside a section of velvet mesquite wood. These larvae are often known as flathead borers due to the shape of their heads. The tunnels that such larvae create in dead wood are of great importance to forest ecology.

Pyrophilous jewel beetles have evolved specialized extra-large wing muscles to enable long distance flights to wildfire sites. These beetles have a way of finding burned trees that borders on the miraculous…

One of the buprestid beetles native to velvet mesquite bosques in southeastern Arizona. Note the heavyset, thickened body of this insect, a specialized morphology that allows room for large, powerful flight musculature.

When they fly, these beetles hold their bodies at an angle, in order to orient their underside to the direction of travel.  Minuscule texturing on the ventral side of the insect’s thorax functions mechanically in response to incredibly faint traces of infrared radiation (heat). Infrared radiation causes a pressure differential to occur in the thorax texturing. This fires neurons, sending a message to the beetle’s brain. The message says “fly in this direction and you will find a smorgasbord of freshly killed trees to provide food for your offspring.” What is even more amazing is that these insects can detect the heat given off by fires at distances up to fifty miles!  (research conducted by Dr. H.P. Bustami and associates at the University of Bonn [in Germany] brought this astounding facet of jewel beetle biology to light.)

A living jewel adorned with iridescent gold flecks and shimmering purple-sapphire elytra, this native buprestid inhabits local mesquite bosque habitats.

This relationship between forests, fire, and beetles has been going on for countless millennia. However, people often take a dim view of beetle larvae drilling tunnels in trees, claiming that this ruins otherwise “valuable” wood. Such anthropocentric views are myopic, for they exclude the needs of all other living things and turn a blind eye toward the ecology of forests. Jewel beetles benefit forests as agents of decomposition; the tunnels that their larvae bore in dead trees provide important open pathways for other insects and for the introduction of fungal spores. The tunnels facilitate the exchange of gasses in the wood and furnish the perfect moist, insulated, dark environ for fungi to take hold. Fungi are crucially important to living trees, to the health of the soil, and for their leading role in the recycling of nutrients via the decomposition of dead trees and other organic detritus. No forest on Earth can exist without fungi and decomposition.

This maze of tunnels was bored by jewel beetle grubs in a dead limb on a living velvet mesquite tree. Read the text above to discover why these tunnels are so beneficial to forest ecology.

This is a limb that was cut from the same tree as the one in the preceding image. However, this limb was cut when it was alive. Note the scarcity of holes and tunnels. Most jewel beetles lay their eggs only on dead wood, but there are a few exceptions to this rule.

Here in the desert southwest, jewel beetles are usually easy to find almost any place where trees are present. I have also found them rather often in upland desert habitats – areas that are essentially treeless. Buprestid beetles fly into these places seeking nectar and pollen meals from the wildflowers and flowering shrubs that grow there. Thus, they provide another important ecological function by acting as pollinators.

A Fascinating New Bird Appears

A few months ago, an unfamiliar bird call became part of the daily biophony here on our home acreage in the Middle San Pedro Valley. As an ever-curious naturalist, I had to know what bird was uttering those strange calls. My wife, Kathleen, had noticed it too. The bird called frequently in the early and late hours of every day, taunting us with its unique, three-note call.

Binoculars in hand, I went looking. I slowly approached in the direction of the sounds, looking patiently and carefully. The local habitat consists of a mature forest of velvet mesquite trees. The sound seemed to be originating up in those trees, but no matter how much I searched, the bird remained unseen. Most often, as I approached too closely, the mystery bird would exit stage left and start calling from a new, more distant location. I tried on another day, and another. Every time, the maker of the calls remained elusive and sequestered.

Velvet mesquite bosque, the woodland where the mystery bird appeared. This is an image from the summer months.

One morning, after hearing the unseen bird again, Kathleen and I decided it was time to explore the  xeno-canto website. I know of no better website when it comes to searching for bird sounds; readers can find it here:  https://www.xeno-canto.org  

I had a growing hunch that we were hearing a thrasher…when we listened to the recordings of crissal thrashers, both of knew that the enigma had been solved.

The crissal thrasher visiting our bird bath on a cold morning when the water had frozen solid. Crissal thrashers average 11 1/2 inches in length. This species is known to form pair bonds (in preparation for the spring breeding season) as early as January. Just two days ago, I noticed that our thrasher had found a companion…

Why hadn’t I seen the bird? I had been looking up in the trees when I should have been looking down, at or very near ground level. The bird seemed to have the ability to “throw” its voice, making the calls sound like they were coming from above. Once we had learned the identity of the bird, we realized that we should have been searching for it on the ground, not up in the trees. Now, we see the thrasher every day as it hides beneath graythorn bushes, foraging for food.

Graythorn is indeed very thorny. Meant to discourage consumption by mammals, the thorns protect the plant, but when it comes to birds, these thorns are an attraction. They spell security from predators, especially raptors.

Crissal thrashers spend much of their time beneath thick cover, using their long, decurved bills to dig and rake away soil and duff in search of insectivorous food. Locally, these birds appear to have a very strong connection with graythorn bushes. Graythorn (Ziziphus obtusifolia) is the most common understory shrub in local mesquite bosques. It grows dense, tangled, thorny foliage, furnishing the perfect place for shy birds to seek cover in. I cannot overstate the ecological importance of these plants with respect to bird life. Many species of birds hide in graythorns, feed from the plant’s abundant berries, or nest deep within its thorn jungle of tangled branches.

At the time of this writing, the graythorn bushes outside my windows are in full flower. The blossoms are minuscule.

After the flowers have been pollinated, berries grow on the graythorn bushes, providing an important food source for many local birds and mammals.

This winter, the Middle San Pedro Valley has been inundated with unprecedented numbers of white-crowned sparrows. There are hundreds on our land every day, and in many other places as well. I cannot walk by any graythorn bush without flushing a throng of white-crowns from within. Like the thrasher, they forage on the ground and use graythorns for cover. Security is imperative to all small birds here, for bird-hunting Cooper’s hawks are present almost every day.