Saguaro boot
Encyclopedia
A saguaro boot is the hard shell of callus
tissue, heavily impregnated with lignin
, that a saguaro
cactus
(Carnegiea gigantea) creates to protect the wound created by a bird's nesting hole. The bird pecks through cactus skin, then excavates downward to hollow out a space for its nest. When the saguaro dies, its soft flesh rots, but its woody infrastructure lasts much longer. So does the hollowed-out callus whose roughly boot-like shape gives it the name of "saguaro boot."
Several different kinds of birds create nest holes
in saguaro cactus. The Gila Woodpecker
(Melanerpes uropygialis) creates small holes (about 5 cm across) at midlevel on the cactus, where the ribs are far apart, feeding on larvae under the cactus skin. The larger Gilded Flicker
(Colaptes chrysoides) drills bigger holes higher up, where ribs are close together, because its beak is strong enough to break through rib tissue.
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 bird's nesting hole requires not only the bird's making a hole but also the cactus's lining the hole - it is not ready for use as a nest until a year after its creation. Many saguaros are home to multiple nests; if birds excavate adjoining hollows, a saguaro boot may be formed with more than one opening.
Native Americans of the Seri group used saguaro boots to store or carry water. It is now illegal to collect saguaro boots from the wild in Arizona.
Some desert moth caterpillars also make tunnels inside saguaro cactus. The resulting dried callus that forms around their tunnels has a flattened disk structure where the caterpillar exits instead of the larger hole seen on a saguaro boot.
Callus
A callus is an especially toughened area of skin which has become relatively thick and hard in response to repeated friction, pressure, or other irritation. Rubbing that is too frequent or forceful will cause blisters rather than allow calluses to form. Since repeated contact is required, calluses...
tissue, heavily impregnated with lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
, that a saguaro
Saguaro
The saguaro is a large, tree-sized cactus species in the monotypic genus Carnegiea. It is native to the Sonoran Desert in the U.S. state of Arizona, the Mexican state of Sonora, a small part of Baja California in the San Felipe Desert and an extremely small area of California, U.S...
cactus
Cactus
A cactus is a member of the plant family Cactaceae. Their distinctive appearance is a result of adaptations to conserve water in dry and/or hot environments. In most species, the stem has evolved to become photosynthetic and succulent, while the leaves have evolved into spines...
(Carnegiea gigantea) creates to protect the wound created by a bird's nesting hole. The bird pecks through cactus skin, then excavates downward to hollow out a space for its nest. When the saguaro dies, its soft flesh rots, but its woody infrastructure lasts much longer. So does the hollowed-out callus whose roughly boot-like shape gives it the name of "saguaro boot."
Several different kinds of birds create nest holes
Tree hollow
A tree hollow or tree hole is a semi-enclosed cavity which has naturally formed in the trunk or branch of a tree. These are predominantly found in old trees, whether living or not...
in saguaro cactus. The Gila Woodpecker
Gila Woodpecker
The Gila Woodpecker is a medium-sized woodpecker of the desert regions of the southwestern United States. They range through southeastern California, southern Nevada, Arizona, and New Mexico.-Habitat:...
(Melanerpes uropygialis) creates small holes (about 5 cm across) at midlevel on the cactus, where the ribs are far apart, feeding on larvae under the cactus skin. The larger Gilded Flicker
Gilded Flicker
The Gilded Flicker is a large-sized woodpecker of the Sonoran, Yuma, and eastern Colorado Desert regions of the southwestern United States and northwestern Mexico including all of the Baja Peninsula except the extreme northwestern region...
(Colaptes chrysoides) drills bigger holes higher up, where ribs are close together, because its beak is strong enough to break through rib tissue.
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 bird's nesting hole requires not only the bird's making a hole but also the cactus's lining the hole - it is not ready for use as a nest until a year after its creation. Many saguaros are home to multiple nests; if birds excavate adjoining hollows, a saguaro boot may be formed with more than one opening.
Native Americans of the Seri group used saguaro boots to store or carry water. It is now illegal to collect saguaro boots from the wild in Arizona.
Some desert moth caterpillars also make tunnels inside saguaro cactus. The resulting dried callus that forms around their tunnels has a flattened disk structure where the caterpillar exits instead of the larger hole seen on a saguaro boot.