Two screech owls peer out from their Saguaro fortress. The giant saguaro (Carnegiea gigantea) is the universal symbol of the American west. These majestic plants, found only in a small portion of the United States, are protected by Saguaro National Park, to the east and west of the city of Tucson, Arizona. Saguaro cacti are host to a great variety of animals. The gilded flicker and Gila woodpecker excavate nest cavities inside the saguaro's pulpy flesh. When a woodpecker abandons a cavity, elf owls, screech owls, purple martins, house finches and black-throated sparrows may move in. Excavated nests form what is called a “saguaro boot”, a hard shell of callus tissue, heavily impregnated with lignin. The saguaro responds to the bird's damaging its tissue by secreting a resinous sap that, over time, hardens into a bark-like shell that prevents the cactus from losing fluid and also protects the nest hole by making it waterproof. The hollowed-out callus whose roughly boot-like shape gives it the name of "saguaro boot." Large birds, like the Harris's and red-tailed hawks, also use the saguaro for nesting and hunting platforms. Their stick nests are constructed among the arms of a large saguaro. In turn, ravens and great horned owls may take over an abandoned hawk nest. Saguaro cacti also provide a valuable source of food for animals. In early summer saguaro flowers provide nectar and pollen for bats that in turn pollinate the flowers. The Mexican Long-tongued and the Lesser Long-nosed bats are the two species that pollinate the saguaro at Saguaro National Park. In mid-summer, ripening fruit provides moisture and an energy-rich food for birds, bats, mammals, reptiles and insects during a time of scarcity. Common wildlife in a Saguaro ecosystem include the coyote, Gambel’s quail, and desert tortoise. In drier areas of the Sonoran Desert, pack rats, jackrabbits, mule deer and bighorn sheep will also eat the young saguaro's flesh when other water sources are not available. Saguaro cacti are only considered an adult when they reach 125 years old, and generally die when they’re 150-175 years old. A first branch may begin at 50-70 years old, although in areas with little precipitation it may take 100 years before a saguaro grows its first arm. Some saguaro may never grow arms. They are called spears. A saguaro must be 35 years old before it can grow any flowers. Saguaros can grow up to 70 feet (21m) tall. Rendered in Poser Firefly without any postwork. Models include: Flink's Skydome, Songbird ReMix Owls of the World and Nature's Wonders Saguaro Habitat