desert

Natural History of Desert Bighorn Sheep

Bighorn sheep adult

Desert Bighorn Sheep (Ovis canadensis) are well-adapted to rugged, rocky desert mountain ranges and canyons. They prefer precipitous slopes and cliffs where they can be safe from predators. They have very good eyesight which helps them navigate steep ledges.

As described by the Arizona-Sonora Desert Museum: “The desert bighorn is a heavy-bodied, gray-brown, deer-sized animal with a large white rump patch. Both males and females have horns, but the males’ are much larger, growing into a curled spiral shape over the course of several years…The ewe’s horns are narrow and only grow about 12 inches long (about a half curl). The male’s horns are broad and massive and eventually curl in nearly a full spiral. The ram’s horns may weigh as much as 40 pounds.”

According to Arizona Game & Fish: “Adult males, rams, weigh between 160 and 200 pounds with a maximum weight of 225 pounds. Adult females, ewes, range from 75 to 130 pounds and average 110 pounds.” An adult has a length of 50″ – 62″ and stands 32″ – 40″ at the shoulder.

The diet of Bighorn Sheep consists of many different grasses, mesquite leaves and beans, desert lavender, fairy duster, desert ironwood, palo verde, globe-mallow, cactus fruits, and agave. In hot weather, they generally eat in the morning, then seek shade to process their cuds. “Bighorns have a complex 9-stage digestive process that allows them to maximize removal of nutrients from food of marginal quality.” In winter, the bighorns can get all the water they need by eating green vegetation. (DesertUSA)

According to DesertUSA: “Males do not defend territories but rather engage in battles over mating access to a particular female. Age as well as horn size determines male dominance status. Rutting season is in the autumn and early winter, and births take place in the Bighorn sheep spring, though mating can last from July to December. Gestation lasts from 150-180 days. One or two lambs are born from late February to May. Within a few weeks of birth, lambs form bands of their own, seeking out their mothers only to suckle occasionally. They are completely weaned by 4-6 months of age.”

Bighorn Sheep have been in the news lately because of a controversial program by Arizona Game & Fish to reintroduce the animal to the Santa Catalina Mountains near Tucson. See the AZGF page: Arizona Game and Fish Big Horn Sheep Website. I have commented on this program in a previous article: Mountain lion dietary supplementation plan.

In California, it’s Bighorns versus renewable energy: “The Bureau of Land Management issued a decision allowing the Soda Mountain Solar project to move forward on developing more than 2,813 acres of public land directly adjacent to the Mojave National Preserve that would cut off a vital route for desert bighorn sheep and damage other desert resources.

This massive, industrial solar array would block the last, best linkage for desert bighorn sheep between the Mojave National Preserve and the Soda Mountain Wilderness Study Area — a key pinch-point for keeping the sheep populations in the preserve connected to populations in the Soda Mountains and ranges beyond.” (Source)

Hunting. According to Arizona Game & Fish:

“Totally protected by the territorial legislature in 1893, bighorn sheep were not legal game in Arizona until 1953, when it was determined that the limited hunting of trophy desert bighorn rams might be the only way to save these animals. Two limited desert bighorn sheep hunts of 20 permits each were authorized, and 20 desert bighorn were taken. Since then, permit numbers, the number of units open to hunting, the number of rams taken, and hunt success have gradually increased. In 1984, Arizona began offering Rocky Mountain as well as desert bighorn sheep hunts. Between 80 and 100 hunt permits are authorized each year, mostly desert bighorns, with hunt success ranging between 90 and 95 percent.”

Bighorn sheep lambSee more photos from the Arizona-Sonora Desert Museum.

See videos from DesertUSA

A new Bighorn Sheep ram was born at the Arizona-Sonora Desert Museum on March 23, 2016. The lamb is active and on exhibit. See video: https://www.facebook.com/desertmuseum/videos/10153628291529315/

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How Tucson Water spends Conservation Fund money and a suggestion for a better way

If you are a Tucson Water customer, you may have noticed an item on the back page of your water bill listed as: “CONSRV FEE $.07/CCF.” This means you are contributing seven cents per cubic foot of water used to a conservation fund. That may not sound like much, but according to an article by Tim Steller, that added up to $2.95 million last year. By the way, this “contribution” to the conservation fund will rise to eight cents per CCF on July 15.

So, how is that money being used? The answer to that question is the objective of a Freedom of Information (FOIA) request filed last January by Mark Lewis, one of five members of the City’s Conservation and Education Subcommittee of the Citizens Water Advisory Committee.

Tucson Water has to date refused to provide the information requested by Mr. Lewis. According to Mr. Lewis, the information requested is “to gather the documentation and information necessary to ensure the funds collected from Tucson Water customers under the Conservation Fee program has been properly accounted for, audited, and expensed.” Mr. Lewis has expressed concern, in his role as an appointed advocate for the Rate Payers of Tucson Water, that the millions of dollars which have been spent through this fund have not been properly tracked or audited and that more recent uses of this fund are not consistent with the purpose of the fund: conserving water.

One conservation program promoted by Tucson Water is the replacement of old toilets with new low-flow models. Tucson Water will give you a $75 rebate toward the cost. According to Steller’s article, “water-wasting toilets remain in around 150,000 Tucson homes, and the program to replace them saved almost 11 million gallons in the first eight months of this fiscal year alone.” Mr. Lewis supports this program, but points out that the small rebate may be insufficient, especially for older homes which may have complicated plumbing issues that would make replacement more expensive.

Another conservation program is rainwater harvesting. Tucson Water will provide a rebate of up to $2000 for installing a system. Steller points out that “those rebates have mostly benefitted wealthier residents and so far have resulted in no measurable reduction in water use.” Mr. Lewis notes that the $900,000 in rain water rebates to date saved no water, but had the same money been spent on wasteful toilets it would have saved 173 million gallons of water to date.

You can read about the program in a brochure provided by Tucson Water: http://www.tucsonaz.gov/files/water/docs/Rainwater_Harvesting_Rebate_brochure.pdf

In that brochure, Tucson Water claims that “45% of the water we use goes to outdoor irrigation.” That number surprises me; I wonder if it is true. The brochure also notes that in order to qualify for the rebate, you have to take a free class. And here is where it gets interesting.

The qualifying class is run by Watershed Management Group, a consulting firm that, for a fee, will design a rainwater harvesting system for you. Three board members of Watershed Management Group, Catlow Shipek, Mark Murphy, and Amy McCoy, comprise three of the five members of the City’s Conservation and Education Subcommittee of the Citizens Water Advisory Committee. The classes are also given by a company that sells rain gutters according to Mr. Lewis. This situation has the appearance of crony capitalism and conflict of interest.

There is another scheme afoot. Tucson City Councilwoman Regina Romero has proposed that $300,000 be used to provide interest free loans to low-income residents so they can plant trees and have them watered by rainwater harvesting systems. Romero is concerned about the “unequal distribution of tree canopy in Tucson…” and its effect on the Urban Heat Island Effect (cities are warmer than surrounding countryside because all the asphalt and concrete absorb heat which makes nighttime cooling much slower). I see two potential problems with this scheme. First, we would have to cover a large part of the city with trees to have any significant effect. Second, all those trees will transpire water, losing moisture to the atmosphere rather than conserving water for reuse.

Given the information above, do you think your forced subsidy is being well-spent?

I have a suggestion on how the money could be spent to actually conserve water.

One of the eco-fads promoted by Tucson Water is rainwater harvesting at residences. So far, that program has resulted in no measurable reduction in water use. But perhaps, if that idea was used on a larger scale, it could help recharge our aquifers. Why don’t we collect storm-water runoff from city streets and in ephemeral flows in the Santa Cruz River and pump that water back into the aquifers via dry wells?

That idea is discussed by Chuck Graf, Senior Hydrologist, Arizona Department of

Environmental Quality in a short article in the Spring Issue of Arizona Water Resource Newsletter (link to article).

This idea is not new. Phoenix began recharging storm-water in the 1930s and now has more than 50,000 wells in operation. Many other communities also use this recharge method. Why not in Tucson and Pima County?

The practice of dry well recharge in Phoenix went largely unregulated until 1987 when legislature directed the Arizona Department of Environmental Quality (ADEQ) to license dry well installers and establish a registration program for existing and newly constructed dry wells. The law expressly limited the use of dry wells to the disposal of storm water. This limitation was intended to prevent disposal of hazardous chemicals into dry wells, which in the past had caused severe groundwater contamination plumes (some of which are still under remediation).

Graf explains the dry well method as follows:

“The dry well borehole is drilled in alluvial sediments, through any intervening fine-grained and cemented zones, into a permeable layer of clay-free sand, gravel, and cobbles. The permeable layer serves as the injection zone for the storm water. ADEQ requires at least 10 feet of separation between the bottom of the injection zone and the water table. Because groundwater commonly occurs at great depth in Arizona’s alluvial basins, installers often have considerable leeway to find an exceptionally permeable zone above the water table that maximizes dry well performance while maintaining a much greater separation distance than the 10-foot minimum.”

Graf goes on to write:

“Potential adverse groundwater quality impact is the biggest concern about dry wells. Although the definitive water quality study probably remains to be done, a number of studies, including a 10-year study in Los Angeles conducted by the Bureau of Reclamation and others, found little evidence for groundwater contamination. A 1985 study in Phoenix found that dry wells had a beneficial effect on groundwater quality with respect to major chemical constituents”

This idea should be considered. Perhaps then, our involuntary contribution to the “Conservation Fund” would actually conserve some water.

END

Our Desert Tortoise

Turtles, tortoises, terrapins are members of the order “Testudines” – what’s the difference? It seems to be a matter of semantics that varies throughout the world. In the United States, Testudines that live in freshwater, oceans, and on land are called turtles. Those that inhabit brackish waters of marshes and river inlets along the coast are called terrapins. The Testudines that are wholly terrestrial are called tortoises.

The Desert Tortoise (Gopherus agassizii aka Xerobates agassizii) occurs from tropical areas in northern Sinaloa, through Sonora, Mexico, in Arizona throughout the Sonoran Desert, and in the Mohave Desert in southeastern California, and southwestern Utah and southern Nevada.

Desert tortoise

 

The Arizona-Sonora Desert Museum (ASDM) describes the Desert Tortoise as follows:

“Tortoises differ from other turtles in having cylindrical and elephantine hind legs and short, broad, club-shaped feet. The genus Gopherus also has flattened forelimbs for digging. The adult desert tortoise can measure up to 14 inches (35.5 cm) in length; the hatchlings are only about 2 to 2½ inches (5 to 6.5 cm) long. The carapace [shell on top] is brown to gray and rounded. The yellowish plastron [shell on bottom] is not hinged and is connected to the carapace at the sides. The male’s plastron is concave at the posterior to accommodate the rounded carapace of the female during copulation. The female’s plastron is flat. Like all turtles it is toothless; the large tongue helps push food back in the mouth. There are no visible ears.”

Turtles are the most ancient of reptiles. They first appeared about 200 million years ago and have changed little. The Desert Tortoise lineage began about 50 million years ago in the Tertiary tropical forests that existed here before advent of the desert.

Desert tortoises in Nevada and Utah generally live in valleys. They dig extensive burrows and live in groups. In Arizona, by contrast, desert tortoises occupy rocky hillsides and generally are loners.

According to ASDM:

“Desert tortoises are well-adapted to withstand the extended dry periods typical of deserts. Although they extract much of their water from the plants they eat, tortoises drink prodigiously from temporary rain pools. They have large urinary bladders that can store over 40 percent of their weight in water and urinary wastes. Urea is precipitated as solid uric acid in the bladder, freeing additional water and useful ions. During periods of inactivity in winter (hibernation) or summer (estivation), metabolic rates, digestion, and water loss from defecation and urination are greatly reduced. As soon as fresh water is available, the solid urates are eliminated from the bladder. Well-hydrated tortoises are able to eat dried plants and store fats in the body. Dehydrated tortoises are physiologically stressed and cannot digest dry plant foods.”

“Tortoises are generally active in times when water stress is reduced (early morning or evening); they can be diurnal or crepuscular depending on temperature and season. Mohave tortoises are mostly active in the spring months from February to May. Sonoran tortoises are primarily active in the summer monsoon months from July to October. Estivation [slowing or ceasing activity] during the hottest, driest parts of the summer helps conserve water because burrows or rock shelters are relatively cool and relative humidity of up to 40 percent reduces evaporation. Without extensive burrows it is unlikely that tortoises could survive the dry Mohave Desert summers. The common defensive behavior of emptying the bladder when molested or handled can have serious consequences in drier periods.”

Desert tortoises are herbivores, but they will eat carrion and insects. They can digest cellulose.

ASDM notes:

“The social behavior of tortoises is relatively straightforward — males fight all adult males and court all adult females they encounter. Mating occurs throughout the summer, although females lay eggs in late June or early July in the Sonoran Desert. Mohave Desert tortoises typically lay a second clutch of eggs at the end of the summer. Retention of viable sperm in the cloaca of the female for at least two years is an excellent survival strategy in non-colonial animals: it ensures fertilization during extended droughts when males are less active or populations crash. The eggs contain all of the water and nutrients necessary for complete development of the hatchlings. Hard egg shells retard desiccation. The normal incubation period of about 90 days in the summer can be much longer later in the year as temperatures fall.”

Desert tortoises can live up to 35 to 40 years. In Arizona, they are protected. They cannot be collected, killed, transported, bought, sold, bartered, imported, or exported from Arizona without authorization by the Arizona Game and Fish Department. ASDM has a tortoise adoption program where you can acquire or drop off a tortoise. Captive tortoises should not be released into the wild because they may carry diseases and introduction may upset the local order of tortoises.

To find out more about ASDM’s tortoise adoption programs go to http://www.desertmuseum.org/programs/tap.php
That site also has more information on tortoise natural history.

Gopher Snakes

Gopher snakes are large, heavy-bodied snakes that often pretend to be rattlesnakes. They are commonly four to five feet long but can get to over nine feet long. Gopher snakes are non-venomous and good to have around because they eat rodents.

At the Arizona-Sonora Desert Museum, keepers removed one gopher snake from the prairie dog enclosure that measured nine feet, two inches long. Guess what it was eating.

Gopher snakes vary in color but are usually yellowish, cream-colored, or tan with many black, brown or reddish blotches on their backs. Check out the top photo here to see the full length pattern. Pretty isn’t it. The scales on their back are ridged rather than smooth.

When disturbed, gopher snakes will hiss, flatten their heads, and vibrate their tails. Because of this behavior and their color pattern, they are often mistaken for rattlesnakes. As you can note from the photos below, gopher snakes have round-pupils whereas rattlesnakes have slit pupils like cat’s eyes.

Gopher Snake

 

Speckled rattlesnake

 

All you have to do is get close enough to look them in the eye to tell the difference.

Gopher snakes have a large range: all of the U.S., southern Canada, and as far south as southern Sinaloa in Mexico. These snakes can be found in deserts, prairies, woodlands, brushlands, (and in my yard), from sea level to over 9,000 feet. They are called bull snakes or pine snakes in some parts of the country.

Gopher snakes are non-venomous constrictors. They hunt during the day except in very hot weather, when they become night hunters. Their prey includes rodents, young rabbits, lizards, birds, bird eggs, other snakes, and yes, gophers. They hunt mainly by sense of smell. Gopher snakes are good climbers and can even climb a large saguaro cactus to check out what might be inhabiting those holes made by woodpeckers. Apparently their tough scales protect them from the spines.

According to the Arizona-Sonora Desert Museum, “Male gopher snakes engage in ritualistic combats during the spring mating season. The combatants remain on the ground, entwined from tail to neck. Each tries to maintain its head and body position, although occasionally they will exert so much force that they roll. Hissing frequently, they rarely bite one another. Presumably the combat ritual is a means of determining the sexual fitness of a male, for usually only the victor will copulate afterwards.” I understand that this combat is performed when a female is nearby.

I have seen similar behavior with rattlesnakes, but instead of remaining on the ground, the ones I saw were intertwined vertically for almost half their length.

The female will lay up to 24 eggs, in the summer, which hatch in the fall.

Gopher snakes use communal dens for winter hibernation.

If you see a gopher snake in your yard, let it be. It may do you the service of eating your pack rats, then move on.

A version of this article first appeared in the Arizona Daily Independent.

See also:

Clever Horned Lizard

Metachromatic spiny lizards

Rattlesnakes

Speckled Rattlesnakes

Venomous Lizards

Creatures of the night- Spadefoots

spadefootDid you hear a bleating cry in the night this summer? Amphibians have a tough time in the desert. But one such critter, Couch’s Spadefoot (Scaphiopus couchi), has it down. Often called “spadefoot toads” these toad-like creatures, to purists, are not “true toads” because, among other things, they lack the toxin-secreting parotoid gland common to true toads. Does that make them false toads? However, according to the Arizona-Sonoran Desert Museum, “Couch’s spadefoots have a skin secretion that may cause allergic reactions in some humans. Cuts and scratches may become painful, and sneezing and discharge from the eyes and nostrils may also result from the handling of this amphibian.” So don’t handle them.

Couch’s spadefoot is about 3 inches long, has smooth yellowish, greenish, or olive-colored skin with irregular spots of green, brown, or black. It is common in the Tucson Mountains and occurs throughout the Sonoran Desert. They seem to prefer well-drained, sandy soil that supports creosote bush and mesquite. They also occur in grasslands, cultivated fields and along desert highways.

The way spadefoots beat the heat is by estivating (hibernating) underground for about 11 months. They come out during the summer monsoon. They are extremely sensitive to low-frequency vibrations caused by rainfall and thunder.  Those vibrations awaken them.

When monsoon rains form shallow, ephemeral pools, the spadefoots get the signal and come to the surface, in some places, tens of thousands of them, on a single night. And they are noisy. As soon as they emerge, the males set up a chorus of bleating that sounds like sheep or goats; the females eat. The males then silently cruise the ponds in search of a female and eat afterwards. Both males and females eat beetles, grasshoppers, katydids, ants, spiders, termites, fairy shrimp, and almost anything else they can find. They have to eat enough in a few days to last them a year.

A single female can lay 1,000 eggs during one night. The eggs can hatch in as little as 15 hours, and tadpoles can metamorphose into tiny toadlets (one could fit on a dime) in 9 to14 days. During the day, the adults use their spaded feet to dig into the mud. Until toadlets are big enough to dig, they seek cracks in which to hide from the sun.

All will feed until the ephemeral pond is gone, then dig into the mud to wait for next year.

 

Creatures of the Night: Grasshopper Mouse

Clever Horned Lizard

Rattlesnakes

Speckled Rattlesnakes

Metachromatic spiny lizards

Venomous Lizards

The Greater Roadrunner, a wily predator

The greater roadrunner (Geococcyx californianus) may have a clownish reputation due to a popular cartoon series, but the roadrunner is a wily predator.

OLYMPUS DIGITAL CAMERA

The greater roadrunner is our largest cuckoo with a body length of 20-24 inches and a wingspan of 17-22 inches. It avoids flying and prefers to run at speeds up to about 15 mph. Even just standing on the ground, it is fast enough to snatch a hummingbird out of the air.

Roadrunners feed on anything they can catch; that includes small birds, snakes, lizards, and mice. Young roadrunners are fed on insects. Roadrunners also eat some fruits and seeds. I recall seeing a roadrunner on my back wall eyeing a family of baby gambel’s quail. Momma quail would have none of this and flew right into the roadrunner, knocking it off the wall.

The roadrunner hunts by walking or running after prey and can jump straight up to capture insects and birds.

According to the Arizona-Sonora Desert Museum:

The pair bond in this species may be permanent; pairs are territorial all year. Courtship displays include, but are not limited to, presenting the mate with a twig or piece of grass and chasing one another.

The nest, which is constructed of twigs, is frequently found in cholla, mesquite, or palo verde. White eggs (three to six) are laid at intervals; if food is scarce the older, larger hatchlings will quickly seize all the food from the parents thus causing the younger, smaller ones to starve. Rarely do all nestlings reach maturity. If not enough food is available, these younger birds will be fed to the other, stronger hatchlings.

Roadrunner skin is heavily pigmented. On cool mornings, the bird positions itself with its back towards the sun and erects its feathers, thus allowing the sun to strike directly on the black skin which quickly absorbs heat energy. This makes it possible for the bird to achieve body heating without unnecessary expenditure of metabolic energy.

Often it seems curiously unafraid of humans. Trotting up close to peer at us, raising and lowering its mop of a shaggy crest, flipping its long tail about expressively, it looks undeniably zany.

Roadrunners are in turn preyed upon by hawks and coyotes, and snakes may go after eggs in the nest. Roadrunners are a signature bird of the southwest. According to Cornell Lab of Ornithology, roadrunners expanded their range during the 20th Century to include southern Missouri and western Louisiana. Unlike the cartoon “beep-beep,” roadrunners have some distinct sounds, listen here.

See 54 more photos of roadrunners from the Arizona-Sonora Desert Museum digital library here.

The greater roadrunner is the state bird of New Mexico. There are many cultural stories about roadrunners. Some Indian tribes believe that roadrunners help ward off evil spirits. Some early frontiersmen believed roadrunners would help lost people find trails. Cowboys tall tales claim that roadrunners would seek out rattlesnakes to pick fights, or would find sleeping rattlers and build fences of cactus joints around them. In parts of Mexico, the roadrunner brings babies, just like the stork is reputed to do in European legend.

Three Desert Squirrels

There are three common squirrels in the Arizona-Sonoran Desert: the rock squirrel, the round-tailed ground squirrel, and Harris’ antelope ground squirrel. I happen to have all three in my yard, although Harris’ is just a visitor.

rock-squirrel

The rock squirrel (Spermophilus variegatus) is the largest of the three, up to 1.5 pounds. It resembles eastern tree squirrels. This squirrel is grey with reddish to brownish tinge, usually on its back. It has a large bushy tail. Rock squirrels are found in many habitats, except for the driest part of the desert. They are true omnivores, feeding on seeds, mesquite beans, insects, eggs, birds, carrion, as well as cactus fruit.

I have seen them kill and eat snakes. Upon encountering a snake, a rock squirrel will stamp its feet and wave its tail from side to side while facing the snake. It also tries to flick sand or dirt in the snake’s face with its front paws. This behavior is called mobbing. Researchers in California note that rock squirrels can distinguish between venomous and non-venomous snakes, and change their mobbing behavior accordingly. Yes, they will attack rattlesnakes. Apparently, adult rock squirrels can at least partially neutralize rattlesnake venom. Rattlesnakes have heat-sensing organs which can detect a difference in temperature as little as 0.01 F at one foot. There is some research that suggests that rock squirrels take advantage of this. The squirrel can pump extra blood into its tail to make the tail warmer than its body, thereby fooling the snake into striking at the tail rather than the body.

Rock squirrels dig burrows and may be colonial or solitary. They can be very territorial. They mate in early spring and produce a liter in March. Sometimes a second litter appears in August or September. The rock squirrel may become dormant, holed up in its burrow during cold times, but it is not known to hibernate.

round-tailed

The round-tailed ground squirrel (Spermophilus tereticaudus) resembles a miniature prairie dog, and like them, is a very social animal that lives in small colonies. It is usually grey to beige with a long, black-tipped tail. Adults weigh 6- to 7 ounces. They inhabit valleys and alluvial fans. The round-tails are primarily herbivores, feeding on grass seed, cactus, and other nearby vegetation such as spring flowers, but they will eat carrion. They may sleep for a few weeks in summer until the monsoon arrives. The round-tailed ground squirrel hibernates in the winter. The round-tails are champion small miners. They may have an extensive tunnel network with multiple entrances. They too breed in early spring with pups born in March or April. The pups usually emerge with their mother by May.

Harris

The Harris’ antelope ground squirrel (Ammospermophilus harrisii) resembles a chipmunk, but it has a white stripe on its side that chipmunks lack (but chipmunks have white stripes on their faces). Also, chipmunks live at higher elevation, not on the desert floor. This squirrel seems to prefer rocky areas. The Harris’ antelope squirrel usually feeds on cactus fruit, seeds, and mesquite beans, but it will take insects and mice. They will climb a barrel cactus to get the fruit in spite of the spines. The Harris’ antelope squirrel is active all year. During hot days, it uses its busy tail to provide some shade. They did burrows about three feet deep where conditions allow.

All three squirrels have sharp, strong claws used for digging. All three are diurnal, that is, they are most active during the daytime. They all have cheek pouches to store food as they gather it. These squirrels have a variety of vocalizations, some quite loud. You might mistake the sound for a bird call.

Barn Owls, Tyto Alba?

Tyto alba is a denizen of the night who stalks his prey by sound and stealth. He may have passed you close by but you didn’t notice, or maybe you felt a brief ghostly presence. On silent wings, the Barn Owl (Tyto alba) can hunt in almost complete darkness, relying only on the faint sounds made by his intended meal. Fringe-like feathers on the leading edge of the wings help make the flight silent.

The barn owl is a very adaptable bird of prey that is found in specific habitats on all continents except Antarctica. It is the most widely distributed land bird. Barn owls eat rodents, and perhaps because we humans attract such beasties, barn owls favor nesting near human habitation in barns, under bridges, in mine shafts, and in palm trees. In the southwest, barn owls also nest in undercuts in arroyos, and may be found in desert grasslands, and in trees around agricultural fields.

Barn owls often swallow their prey whole, but they can’t digest fur and bone, so they regurgitate pellets. (Dissection of pellets allows researchers to study what the owls eat.)

Barnowl-female

 

 

 

 

 

 

 

 

 

 

Barn-owl-male

Barn owls are sexually dimorphic, that is, the males and females have differing plumage as you can see in the photos. The females tend to be bigger, darker, and more speckled than the males. The birds average about 12 inches in body length and have wingspans of about 33 inches. Weights in adults vary from 10 to 20 ounces.

The feathers form a facial disk designed to focus sound to the owl’s ears. The ears themselves are not symmetrical on the skull as in other animals. Rather the left ear points downward, and the right ear points upward. Therefore, sound reaches each ear at slightly different times and allows the owl to exactly pinpoint the source. Some researchers claim that each ear hears with slightly different frequency sensitivity. That also aides in sound location. Barn owls are smart and learn all the squeaks and twitters of their prey so that they can identify not only where it is, but also what it is. Perhaps the only rodent with equally good hearing is the Kangaroo Rat.

Birds have four toes or talons. They are configured either three in front – one in back, or two and two. The barn owl can move its outer toes to form both configurations. That enables the owl to form a good web-like trap when snatching prey. The barn owl has serrations on the claw of the middle toe to aid grooming.

Barn owls have many vocalizations, some researchers count as many as 15 distinct calls as well as tongue clicking and wing clapping. Some of the sounds are for proclamation of territory, others are for alarm, and some are for courtship and mating rituals. Many of the sounds are screaming or screeching; others include hissing or wheezing, and whistling. None of the sounds are what we would call an owl hoot.

Nesting occurs in the spring in most areas, but can occur any time of year if there is abundant prey available. The female may lay up to six eggs each one to two days apart. Incubation takes 33 days and the young hatch one to two days apart. If the parents don’t provide enough food, the older chicks starve out and may even consume the younger chicks. The chicks will fledge seven to eight weeks after hatching. Barn owls typically breed at an age of one year, and there is a high mortality rate in the wild. Typical wild life expectancy is 2 years, but captive birds have lived into their high teens.

Barn owls are difficult to observe in the wild because of their nocturnal habits. I have seen them sleeping in mine shafts. If you want to seem them close up, go out to the Arizona-Sonora Desert Museum where Docents frequently have them on display.

Barn-owl-chicks

Creatures of the Night: Kangaroo Rat

Of all the mammals in the desert, the kangaroo rat is perhaps the best adapted to arid conditions: it never needs to drink, nor eat fresh vegetation; it can metabolize water directly from dry seeds.

kangaroo-rat3

The diet is almost exclusively seeds, and it prefers seeds high in carbohydrates rather than seeds high in fat or protein. That’s because metabolizing fatty seeds produces heat, and metabolizing protein-rich seeds requires more water to get rid of nitrogen-rich waste products.

The K-rat stores seeds in its burrow where they absorb any humidity, thereby giving the rat some extra moisture. The K-rat has no sweat glands through which to lose water.

The kangaroo rat minimizes moisture loss during respiration with its specialized nasal passages which function as counter-flow heat exchangers. These passages warm the air during inhalation, then cool the air and extract moisture during exhalation.

The kangaroo rat can conserve water by producing urine about 5 times more concentrated than human urine. The rat also produces very dry feces pellets with about one-fifth the water content of a white lab-rat’s pellets.

The kangaroo rat is 4- to 5 inches long with a tail up to 10 inches long. It prefers to hop on its hind legs. It can jump 10 feet and change direction immediately upon landing, something that helps it avoid nocturnal predators.

Although the rat has tiny external ears, the middle ear chamber is highly developed and may be bigger than the braincase itself. This allows the rat to hear low intensity and low frequency sounds such as an owl flying or a rattlesnake ready to strike. This, together with its ability to jump 10 feet, helps it avoid predators.

Creatures of the Night: Grasshopper Mouse

Mice will eat just about anything, but most prefer plant parts. The grasshopper mouse, however, is a ferocious carnivore. It eats grasshoppers, beetles, spiders, centipedes, millipedes, worms, lizards, scorpions, snakes, and other mice. It hunts like a cat and defends its territory by howling – it is the mouse that roars.

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There are several species and most inhabit the grasslands of the great plains, but at least one species is a desert dweller. The Northern Grasshopper mouse has a range from Canada to Mexico, and California to Minnesota; the Southern Grasshopper mouse has a range that includes parts of Nevada, Arizona, New Mexico, and Texas. The southern species is gray-brown- to cinnamon colored with a short white-stripped tail. Most grasshopper mice are relatively stout compared to other mice. The head and body is 3.5″- to 5″ and the tail is 1″ to 2.5″ long.

Usually a male-female pair live together and defend a territory. It marks the territory with musk.

Grasshopper mice have very strong jaw musculature required for killing prey. And they learn quickly how to deal with various prey. One observer describes how the mouse dealt with a 3-inch scorpion in Arizona: ” The mouse would first nip the tail so that the stinger was ineffective. It would then stand the scorpion on end, holding it with its front paws, and methodically eat the writhing creature head first.”

The grasshopper mouse is a nocturnal hunter, a good climber, and active year round. In some areas, scorpions account for almost their entire diet, which might be surprising because the mice are not known to have any immunity to scorpion venom.

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These mice will eat seeds, grasses, and grains, and cache them, like other mice, but about 90% of their diet is animal matter. The strangest part of their diet is sand. Biologists think the mice eat sand to aid in digestion, just like some birds ingest gravel. And that’s not all that is strange about their digestive system. As described in an article by Mary Ingle: “A pouch attached to the underside of the stomach opens into it via an aperture too small for large food particles to pass through. The pouch contains all of the gastric glands that contribute to the breakdown of food and are normally found in the stomach of other mammals.” Ingle speculates that the pouch exists because the insect diet would be too rough and damaging for delicate gastric glands to function normally.

The grasshopper mouse digs four kinds of burrows: nesting, retreat/sleeping, caching, and the bathroom.

The mice have several vocalizations. You may have heard their territorial proclamation and mistaken the high-frequency sound for that of an insect. So now, when you are out at night, listen for the mouse that roars.

For a video of a battle between a grasshopper mouse and a very large centipede check here: http://tinyurl.com/ylyme9w Note that centipedes are venomous.