Arizona Snakes

Humans, and many other species, are born with a ready-made instinctive fear of snakes.  All it takes to activate the instinct is seeing an adult being afraid of a snake.  Many people overcome their fear after learning which snakes are dangerous, and which ones are harmless.  This is a good thing for snakes, and it’s good for everybody else, because snakes are necessary for a balanced ecosystem.  Snakes help regulate populations of rodents, frogs, and other small animals, and snakes serve as food for many birds, mammals, and reptiles.  The references include field guides in print (Stebbins 1966) and online (Arizona Herpetological Association (AHA), Brennan, 2008).  AHA and HerpDigest provide news and information.

About half the snake species and recognized subspecies in the U. S. are present in Arizona.  Many of them are present in the Agua Fria River Basin, but the only ones I see around Coldwater Farm are garter snakes, gopher snakes, and king snakes.  It’s odd that over the past 50 years, no one has reported seeing a rattlesnake on the Farm.  They are probably present, but most rattlesnakes are shy and rarely advertise their presence.

The photograph shows a California King Snake, a common species of the Agua Fria River Basin and Coldwater Farm.  The photo is from the website of the Arizona Herpetological Association.

Arizona Lizards

Almost half the lizard species found in the U. S. are present in Arizona.  They are a colorful group with fascinating life histories.  Lizards help control ants, termites, and other insects, and with only one exception, the Gila Monster, they are unable to seriously harm humans.  Field guides are available online (Arizona Herpetological Association, Brennan, 2008), and in print (Jones and Lovich, 2009, and Stebbins, 1966).

The most common species seen around homes in the upper Agua Fria River Basin where I live are the Plateau Fence Lizard, the Ornate Tree Lizard, and several Whiptails and Horned Lizards (HLs–also called horny toads).  Here they are active from March to November.  In the Sonoran Desert at the south end of the Basin they are active all year.  Lizard body temperature is controlled by surroundings rather than by internal systems.  Without warm air, sunlight, or sun-warmed surfaces, they have to find shelter.

The photograph shows a Plateau Fence Lizard on a tree.  These lizards do like fence posts, but they will sit on any convenient object that gives them an elevated view.  

Barn Owl Near the Agua Fria River

A few days ago, I brushed by the spruce tree beside the house and a Barn Owl (Tyto alba) flapped out.  It perched in a nearby Cottonwood tree and watched nervously while I took photographs.  I have known for years that there was a Barn Owl living nearby.  Seven years ago I found a brown and white Barn Owl feather lying in the front yard.  Since then I’ve seen silhouettes in trees and sailing silently across the yard.  Two years ago a second feather turned up.

Barn Owl at Coldwater Farm near the Agua Fria River

The second Barn Owl feather

Invasive Species:  Our Accidental Attack On Nature

The story of invasive species and their alteration of native habitats is one of the most disappointing tales to be told of human interaction with nature. It is full of surprises, unsolved mysteries, scientific research, and reactive management that too often exemplifies the adage, “too little too late.” This post summarizes the main elements of the plot and its conclusion. It begins about 500 years ago when people started crossing the oceans and taking boatloads of new species to North America and other parts of the world. Some of the new species invaded native habitats, replaced the natives, and became permanent residents. Of all the things people have done to the wildlife and wildlife habitat of the Agua Fria River Basin—road and building construction, ranching, logging, hunting, farming, fertilizing, recreation, burning, and water use—the most destructive has been the accidental introduction of invasive plants and animals.

The photo shows the dry seeds of Horehound (Marubium vulgare).  The seeds have small hooks that catch on clothing and animal fur. Horehound is a small perennial shrub that forms pure stands when native vegetation is removed by livestock. The seeds often create persistent mats in animal fur, and they are irritating when they get in your socks. Cattle will eat a little Horehound when the plants are young, but they don’t eat enough to prevent the plant’s spread.

Loggerhead Shrikes (Lanius ludovicianus) are fairly common in the Agua Fria River Basin, but the one shown here is the first one I have photographed.  This fellow was quite curious about me, and while I stood talking to him, fluttered to within about ten feet, then perched nearby while I tried for a good camera angle.

Male and female shrikes share the same white,  gray, and black plumage, and both parents feed their young.  This big-headed little bird hunts insects and small lizards, mammals, and birds from fences, trees, and shrubs.  Shrikes have strong beaks but relatively weak talons.  When they make a catch they carry their prey to a thorny tree or shrub, impale it, and tear it asunder with their powerful beaks.  If prey is plentiful, some will be left impaled for later use.  These ‘left overs’ are perhaps used to mark territory and attract females.

Loggerhead Shrikes have declined throughout the United States, especially in the Midwest and Northeast.  Breeding bird surveyors (Corman and Wise-Gervais 2005) found the bird nesting throughout Arizona, but according to Sauer et al. (1995), there has been a measurable decline.  Roads, pesticides, and other threats are discussed by Julie Craves (2007).   Shrikes prefer open woodland and shrubland with abundant perches and thorny plants.  As these habitat types fade away due to the spread of invasive weeds and the increase in wildfires, shrikes will become scarce.  But until the chaparral is burnt out and the megapolitans arrive with their bulldozers, you can see these unusual little birds just about anywhere in the upper Agua Fria River Basin.

References (Look for additional references in the earlier post on Arizona Birds)

Corman, T.E., and C. Wise-Gervais. 2005. Arizona breeding bird atlas. University of New Mexico Press, Albuquerque, NM.  636 p.

Craves, J.  2007.  Species profile: Masked predator, Loggerhead Shrike.  Birdwatching.  August 22, 2007.  Online in the bird profiles section at:  http://www.birdwatchingdaily.com.  (On the BirdWatchingDaily website go to ‘getting started–bird profiles–August 2007 edition.)

Sauer, J.R., S. Orsillo, and B.G. Peterjohn.  1995.  Geographic patterns and population trends of breeding and wintering Loggerhead Shrikes in North America.  Proceedings of the Western Foundation of Vertebrate Zoology 6: 128-141.

Arizona Ants

Ants are a critical component of the earth’s terrestrial ecosystems.  They consume and break down large amounts of material, they control the populations of numerous species, and they provide food for many others.  For instance, ants make up 40% of the diet of the Northern Flicker, a common Arizona bird.  Despite being small and not so visible, ants account for 15% to 25% of all animal biomass on our planet’s land surface—far more than any other animal group.

So how much do the ants weigh?  Using guesstimates from the references I made assumptions that the average ant weighs .004 grams, and that there are 1,000,000 ants per human.  Thus, the earth’s ants weigh around 21 billion tons (I didn’t try to use dry weight).

Not to be beaten by these little bugs, however, humanity is increasing its weight at a rapid rate.  Issac Asimov once (Asimov 1975) estimated that if our numbers continued to grow at the 1970′s rate of 2% (doubling in 35 years), the mass of humanity would match that of the whole planet in about 1500 years.  Probably no ants (or any other animal) could survive this.  Of course, our birth rate is declining, and even though our life expectancy is increasing, doubling our numbers will take longer and longer.  If we assume that the average human weighs 120 pounds, our species currently weighs 420 million tons.  If we double every 100 years, and if we do not destroy any ant habitat (OK, that is not a reasonable assumption.  Nevertheless…), we would weigh more than the ants in 600 years.

The photo shows Myrmecocystus navajo, a member of the Formicinae subfamily.  This one was collected in Yavapai County, Arizona.  The photo may be by Barry Bolton, but it could be by Stefan Cover or Bob Johnson.  It is from the AntWeb website.

Arizona’s premier mammal species, and one of the very youngest, the humans (Homo sapiens), congregates in urban habitats that most other mammals avoid.  Residents of the scattered human homes of the Agua Fria River Basin often see the 15 to 20 common species that are active during the day and early evening.  Residents of large urban areas such as Phoenix and Tucson rarely see more than three or four species.

Developers are eager to fill the Agua Fria River Basin with homes and businesses.  As the human population of the Basin grows, the number of familiar mammals will decline.

Of course, almost all species decline as the human population grows.  When I began high school in 1960, the human population of earth totaled three billion.  Forty years later in 2000, it had doubled.  From 1960 to 2000 the U. S. population grew from 180 million to 280 million, and will add more than 100 million during the next 25 years.

In Arizona the extinction of other species by humans is occurring most rapidly for species that spend much of their lives in or near water (look at the blog posts on fish and amphibians).  This is because toxic wastes flow down slope to the streams and lakes, and because the streams and lakes are being modified.  Over the next 100 years many species will disappear.  Mass extinctions have occurred before in Earth’s history, but it is likely that none were as large or sudden as the one that is being caused now by humans.  Certainly no other single species has ever achieved such a great destruction of life on earth.

Mammals are described in numerous field guides and websites (e.g., Kays and Wilson, 2002, National Wildlife Federation, AZGDF).  Field guides often illustrate animal tracks, and some (e.g., Halfpenny 2000) are devoted to this essential subject.  A complete field guide to Arizona’s 144 mammal species can be assembled and downloaded from the North American Mammals page of the Smithsonian Institution’s National Museum of Natural History web site.  The downloaded field guide will have a page for each species with a picture, distribution map, and description.

The photograph shows a Rock Squirrel sitting on a fence post.