I am happy to report that the Middle San Pedro Valley has finally received some summer rain! This has been a very dry summer – during July and August, we have received only .63 inches of rain. Most of that has occurred during the past four days. The summer “monsoon” season is what literally defines this ecosystem – enabling much of the rich assemblage of plant and animal species that makes this part of Arizona such a remarkable place.
Despite the extended drought, the velvet mesquite trees in the local bosque have put on a tremendous spurt of foliar growth this year. Additionally, the trees have flowered three times since spring. As I write this, the ground under the trees is plastered with a heavy crop of “beans,” the nutrition-packed seed pods that are one of the cornerstone food sources for our wildlife. How can this happen during such a bone-dry, hot spring and summer? The answer is rooted in last year’s very wet monsoon season. Mesquites have a remarkable ability to move rainwater down their roots, where they store it at depth for later use. That’s right; these trees can move water in both directions in their root systems! The big bean crop owes its genesis to last year’s stored rain water.
Wind plays a pivotal role in the ecology of velvet mesquite trees. When the seed pods are ripe, winds accompanying rain storms can release astounding quantities of pods in very short periods of time. Pods on the ground then become available to all wildlife, not just the species that climb trees. Mesquites depend upon animals to remove the tough outer seed coating by chewing and gnawing on the pods. The seeds of mesquite trees are able to germinate only after the outer husk is removed. This beautiful bumblebee appeared last week, an uncommon insect in local bosques. The ecology of bumblebees is intimately woven around the activities of small rodents. Local bumblebees make their colonial nests in the abandoned underground nests of mice and kangaroo rats.
Iridescent scales glitter on the back of this Clark’s spiny lizard, at rest in the shade of my ramada on a 108°F. day. Prime habitat for this species are mesquite bosques, where the trees offer an abundance of shade and escape routes from predators. Clark’s spiny lizards can climb trees with the speed and agility of an over-caffeinated squirrel.
Within the sheltered confines of a small depression in the joined trunks of two mesquites is a small rodent’s dining room – in this case, likely an Ord’s kangaroo rat. Note the many chewed fragments of mesquite pods. Kangaroo rats and many species of mice prefer such places to gnaw on their foods.
As of this writing, the raven family is still together as the trio of young birds explore their new world, constantly learning from their devoted parents. That’s papa Mike in the foreground, Mavis in the background, and their rowdy, inquisitive kids in between.
Mavis eyes up one of her favorite foods. Large eggs like this one must be held in the bird’s beak with skill and finesse. She sauntered off with this one, walking some 90 feet into the bsoque, then gently dropped the egg, dug a hole, placed the egg into the hole, then covered it with soil and duff. The spatial cognition and spatial memory of ravens is astounding. Hundreds of food items get stashed in tree crotches or buried for later use – with uncanny ability, the ravens remember where every one of them is hidden. This morning brought us a seldom-seen spectacular visitor in the form of this Gila monster that was crawling along the foundation of our home.
When viewed dorsally, the reticulated patterns on the backs of Gila monsters really stand out – patterns that are mirrored in the art of many native southwestern cultures and tribes. No two Gila monsters are patterned alike, so photographs can identify specific individuals. This one is an adult, about 14 1/2 inches in length.
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.
