Tumacácori National Historical Park is located in southern Arizona which makes it a part of the Arizona Upland division of the Sonoran Desert - an ecosystem which covers the southern third of Arizona.  The Sonoran Desert is home to a great diversity of plant species as well as animals and birds.  It is a subtropical desert with a biseasonal pattern of rainfall.  Differences in topography, soils and climate determine which plant species will do well in a particular area.

Although one expects to find cacti in the desert, the number and variety found in this region is truly astonishing.  Cholla cacti - buckthorn, cane, jumping, teddy bear and pencil - blanket the dry, sandy soils of valleys, plains and slopes of the region.  These cacti are very spiny and are characterized by jointed branches which are easily detached if you happen to brush against them!  They are difficult to remove from skin and clothing - try a stick or a comb, but not your fingers.  The ground hugging prickly pear serves as food for desert animals - particularly the javelina - which doesn't seem to mind the spines!  Barrel cactus can help you find your way in the desert as they always point towards the south in this area. Towering magnificently above everything else in the desert is the saguaro cactus.  The saguaro, the state flower of Arizona, is a very slow growing but long-lived cactus, with some plants estimated to be 150 to 200 years old.  By the time a saguaro is 14 years old, it is only six or seven inches tall.  It takes the saguaro 35 to 40 years to reach six feet.  By the age of 85, the saguaro is usually 25 feet or taller.  Of course, frost, lightning, animals and man can make a difference in these growth patterns.  The saguaro has adapted well to the desert environment - its pleated sides expand to store vast quantities of water for use during droughts.

Along with the cacti, shrubs and trees dot the landscape of the Sonoran desert.  The aroma of the creosote bush is quite pungent after a rain.  Bur sage with its triangular leaves, brittlebush with its bright yellow flowers on long stalks, limber bush with its reddish branches and bright green, heart shaped leaves, and fairy duster, with its dense flower heads of pinkish puffs, add a variety of colors to the landscape when they bloom and shades of green when they are not blooming. Foothill palo verde, desert ironwood, velvet mesquite and ocotillo offer shade although their individual leaves are quite small.  The foothill "yellow" palo verde is easy to spot because of its smooth, yellow-green bark and absence of leaves during most of the year.  The desert ironwood, by contrast, has a gray bark that ranges from smooth to heavily fissured and scaly.  The wood from this tree is extremely dense and will not float in water.  The velvet mesquite with its dark brown rough bark is a favorite wood for fuel in the desert and for fence posts.  The ocotillo has a unique adaptation to its environment - leaves appear only after a rain and wither when the soil dries.  Of course, it repeats this process several times during the year.

The animals of the desert have adapted quite well to their environment.  Some animals hide in cactus holes, underground burrows, or other cool and shaded spots during the day.  Other animals prefer the daylight hours, but even they are less active during the heat of the day.  They tend to restrict their activity to early morning and late afternoons. If you look carefully beneath shrubs, you may see a grayish brown Antelope Jackrabbit seeking shelter.  This rabbit's long ears help it to regulate its body temperature - a key to surviving extremes of temperature in the desert.  Coyotes and javelinas are even more adaptable since they are active at any time of day or night that is not too hot.  One can always tell when coyotes are roaming the desert at night.  All one needs to do is listen for their distinctive vocalizations - barks, yelps and a prolonged howl!!

Many animals which are almost to small to see also inhabit the desert of this area.  Scorpions can be a painful reminder of a visit if one is not vigilant, however they are usually more active at night.  Spiders, too, live in this area. Tarantulas, although not very appealing to look at, are fascinating to study.  These spiders are usually reluctant to attack people, but when they do, their venom is no more poisonous than a bee sting.  Small lizards abound - look for them on the walls and walkways.  The side-blotched lizard, 4 to 6 inches long, and the swift running zebratail lizard, 6 to 9 inches long, both feed on insects as part of their diet.  Larger lizards such as the gila monster and the western whiptail can be spotted by the patient observer.  The gila monster, 18 to 24 inches long, is a venomous lizard whose poison flows into the open wound the lizard creates as it chews on its victim.  The western whiptail, 8 to 12 inches long, digs burrows for a retreat and to find prey.  But the whiptail will stalk any small moving object, including a fluttering leaf!  Even snakes inhabit this area, although they usually hide during the heat of the day.  Many of the snakes are harmless, but there are some Western Diamondback rattlesnakes here that one must be cautious of.

The birds of the desert, like the other animals and plants, have had to adapt to their environment.  Many make their nests among the spines of a cactus or utilize burrows and holes created by other animals.  The  fountain in the garden at Tumacácori National Historical Park is an inviting place to sit and observe the birds.  The fruit trees are a ready food source for them and the burbling water is almost too much for them to resist!  Look for grayish brown birds with long curved bills running on the ground in search of insects - that's a curve-billed thrashed.  The noisy woodpecker with the black and white striped back you see is the ladder-backed woodpecker.  The Santa Cruz River nearby is also a bird lovers paradise.  The trees offer not only shade for humans, but shelter also for the birds.  It is not unusual to see a roadrunner sitting and watching the humans carry on their tasks at the park while waiting for a lizard to cross its path.  Check out the tops of tall plants and telephone poles for hawks, common ravens and turkey vultures.  Once the desert air heats up, you'll notice the turkey vultures riding the thermals as they search for food.

Birdwatchers can pick up a Birding Check List from the Visitor Center.