This has been one of the driest and hottest summers I can recall here in the Middle San Pedro River Valley. During “normal” summers, monsoon rains arrive between the middle and the end of June and continue through August and much of September. The two previous monsoon seasons brought us a welcome abundance of rain, but this year has remained very, very dry. Daytime highs for the past six weeks have averaged around 106°F., with more than a few days reaching 110° or higher. This year’s highest temperature registered at a crispy 115°F. on July 17.
Our mesquite bosque remains dry, the understory of dense London rocket plants yellowed and brittle. Usually, by the end of July, this scene should be bursting with vivid green growth in the form of Amaranthus palmeri and many other native plant species.Despite our xeric summer, velvet mesquite trees in our bosque have produced a nice crop of pods, followed by a second flowering during the past couple of weeks. The trees are drawing on water from last summer’s abundant storms; mesquite has the rare ability to transport water in both directions within its extensive, very deep root system. Water can be transported deep underground and stored for later use. A fresh splay of velvet mesquite blossoms perfumes the air and reminds us that desert plants have evolved uncanny mechanisms to stay alive and even thrive under dry, difficult conditions.
Mesquite blossoms lead to garlands of bright green pods growing from pendant branches. Mule and whitetailed deer love to feed on low-hanging bunches of these young pods. When ripe, the seed pods turn yellow and fall to the ground. There, they become one of the most crucial and nutritious wildlife foods in the entire ecosystem, eagerly fed upon by a very long list of native animals from mice to coyotes to bears and many more.
Despite the drought, this was a banner year for a widespread local species known as catclaw acacia, Acacia gregii. (See the photos in my previous blog post.) Throughout the valley, these large shrubs/small trees flowered explosively. The scent from their blossoms is intoxicatingly wonderful. Much like mesquite pods, the seed pods of acacias are fed upon by a wide variety of native wildlife.
Dry conditions leave fine coatings of dust on our driveway – an excellent newspaper that I strive to read daily. This summer has revealed tracks of mice, kangaroo rats, gray foxes, coyotes, raccoons, mule and whitetailed deer, a cougar, hooded skunks, quail, doves, and other birds including this trackway of a Chihuahuan raven.A closer look at the raven’s tracks reveals their relatively large size, distinctively lobed feet, and shallow drag marks made by their posterior claws.
A mystery…last week, I noticed something I had not seen before: dense clumps of small, black native bees forming in certain graythorn (Zizyphus) bushes. I have no idea what is going on here, nor what species these bees are – there are well over 1,200 species of native bees in this ecosystem, representing the richest known bee fauna in the world.
I found this adult giant mesquite bug (Thasus californicus) roaming under my ramada the day before I posted this blog. These are large insects that are true bugs (Hemipterans) as opposed to a type of beetle (Coleopterans).
A lateral view of the mesquite bug reveals the tube-like mouthpart that it uses to feed on plant liquids. The tube is inserted, syringe-like, into the stems of plants. These specialized feeding tubes are a primary characteristic that separates true bugs from beetles.
Prior to maturation, giant mesquite bugs exist in the form of wingless nymphs. The nymphs form colonies that feed on liquids from various species of trees and shrubs. The nymphs go through several instars before finally transforming into adults, all of which exhibit these very bright red colors. The nymphs are protected with self-manufactured noxious chemicals that make them taste bad to predators, hence their aposematic coloration.
Arizona’s smallest mammals are shrews; I found this one – dead but still warm – on the floor of our bosque. This species is known as the desert shrew, Notiosorex crawfordi. Shrews are among the most highly energized, frenetic mammals on Earth. They require remarkable amounts of food – up to nearly half their body weight on a daily basis. They almost never stop moving, constantly on the hunt. I wonder how they have time to dream.
This sight greeted me a few mornings ago, when I walked outside just after dawn to see this giant centipede (Scolopendra heros) clinging to the wall of my adobe building. The broom handle gives a sense of scale. This one was just under seven inches long – and they get bigger than this, up to nine inches in length. Very large specimens measure around an inch in width across their backs, are equipped with formidable pincers, and can move at astounding speeds.
High winds snapped this velvet mesquite trunk at the location of a cavity hollowed out by Gila woodpeckers. I have seen such tree breaks many times, both locally in this southern desert and in the northern Rockies. There is a complex relationship between cavity-making birds and their varied roles in forest ecology that may be more important we know.
A close look at the exposed woodpecker cavity shows the remnants of a successful nesting season. Last month, a pair of ash-throated flycatchers raised a batch of young within the sheltered confines of this tree cavity.
This image should be entitled “HOPE”… a series of empty, dry water buckets under my roofline, hoping and waiting for the summer rains. Why collect rainwater when we have a well, particularly summer rain water? The summer storms often feature stunning amounts of lightning, which allows substantial amounts of elemental nitrogen to be carried from the atmosphere (via rainfall) down to the ground, where it greens the Earth. All gardeners should learn that summer rain water collected after lightning storms works magic on plant growth.
The Middle San Pedro Valley sprawls across nearly one million acres of undeveloped, unfragmented land in southeastern Arizona. Its slopes and woodlands, bajadas and ridges have been rimed with frost every dawn under the abbreviated touch of winter’s Sun. Days are short. The land stands hushed and still with its seasonal absence of many birds, reptiles, and other forms of life. Nonetheless, there are many good reasons to get outside and walk the land. January and February have brought a few surprises, particularly in the way of unexpected sightings of locally uncommon birds.
In late January, five purple finches began frequenting our bird feeders, thinking they were well concealed within mobs of house finches and lesser goldfinches. My wife’s sharp eyes picked them out of the crowd. In 20+ years of avian record keeping in this valley, that was the first time we had ever seen purple finches. Another species that has been sighted sparingly here during the winter months is the American robin. For reasons that remain a mystery to me, we have been inundated with robins this winter. They bring me many fond memories of their near-constant presence during past summers when I lived in the northern states.
Speaking of thrushes, another bird that I had never seen in the valley before has arrived to grace the nearby riverbottom woodlands this winter – a Townsend’s solitaire. A friend and neighbor, Tom Talbott, first sighted one about a week ago in the forests along the river not far from our home. Tom is a highly skilled birder and a masterful wildlife photographer. A few days later, walking the same reaches of the river, a friend and I also saw a solitaire. News has been spreading of numerous sightings of this species in areas just a few dozen miles to the north.
A Townsend’s solitaire perches quietly in branches overhanging the channel of the San Pedro River. These elegant thrushes are common residents of timberline forests high in the mountains of western Montana, where I would meet them again and again as I led groups of hikers during the summer months. Their songs are unique and unforgettably angelic, like no other bird I have known. Photo courtesy of Tom Talbott.
Not far from the solitaire, we found this great horned owl snoozing within the branches of a Fremont cottonwood. These owls are remarkably capable predators whose list of possible food items exceeds that of any other North American owl. Among the creatures that great horned owls have been known to prey upon include insects, amphibians, various reptiles, mice, rabbits, domestic cats, small dogs, ducks, skunks, and even porcupines.
Mid-January brought us over an inch of rain in the valley floor during one winter storm. Rainfall amounts were much higher in the nearby Galiuro Mountains, resulting in a strong winter flow for Hot Springs Wash. Such flows during the winter months are rare.
The rain enabled millions of dormant London rocket (Sisymbrium irio) seeds to sprout, providing a new source of food for wildlife while greening the floor of this mesquite bosque with the glowing color of new life.
Large numbers of these small white puffballs erupted from the ground under mesquite trees after the rain. Fungi are becoming known as some of the most important organisms on the planet. The mycorrhizal filaments of many species of fungi form mutually beneficial associations with tree roots, for example. No forest on Earth can exist without such subsurface fungal alliances.
A hooded skunk wandered under my ramada one night, leaving its signature behind in the form of these tracks made in fine, dusty soil. Note the track pattern as the animal was walking at normal speed.
A closer look at the skunk’s footprints. Even though skunks are plantigrade mammals, the heels on their back feet often do not register in their tracks, as seen here. (The hind foot is to the left, front foot to the right.)
I discovered this torpid spiny lizard spending the winter brumating underneath a plastic tub that had been set outdoors on the ground. The lizard was found at ground level, not dug in below the frost line. Temperatures here routinely dip into the teens every winter. I was taught that reptiles must spend winters below the frost line, because otherwise they would freeze and die. I have also seen a pair of diamondback rattlesnakes spending the winter under a board in an open barn. Apparently, what I was taught cannot be correct – it seems clear that these reptiles can endure a fairly substantial amount of freezing.
