See the context of this sign.

Saguaro - Guardian of the Desert

Mature saguaros dominate the Sonoran desert as
living examples of the interdependency necessary
for both plants and animals.

The saguaro is an ideal residence for birds, bats
and bees, which find the internal temperature 20
degrees cooler in summer and correspondingly
warmer in winter. Nests deserted by the Gila
woodpecker or gilded flicker become home to
screech and elf owls, while red-tailed hawks nest
on saguaro arms.

Saguaro blossoms, open less than 24 hours for
pollination, rely on the instincts of birds, bees and
other winged insects by day, and moths and bats
at night. Even this massive effort is not enough to
guarantee that the seeds, as many as 22 million
produced in a lifetime, will take root.

Some saguaro seeds are eaten by birds, which find
them indigestible and void them, often when
perched in mesquite or palo verde trees. The
young cacti growing from these seeds then receive
the shelter needed for their early growth.

Don't miss the rest of our virtual tour of Saguaro National Park in 687 images.