This past Feburary I watched a Gila Woodpecker male, identified by the red patch on his head, creating a cavity in a saguaro. He reared back his head and used the leverage afforded by his long tail to hammer at the green skin of the cactus, breaking through the outer layer.
After that, things went easier. He quickly enlarged the hole, reaching inside with his formidable beak to scrape and probe, pulling his head out to shake off the juicy bits of saguaro flesh. Soon, the woodpecker had excavated the cavity enough that he was leaning far inside to do his work.
Once the cavity is 9-18 inches deep, the Gila Woodpecker leaves it alone to cure. The inner parts of the saguaro callus over in a couple of months forming what is called a boot. Then the nest is ready for use. Unless someone else moves in first, the female woodpecker lays three to four white eggs in the bottom of the bare cavity.
Sometime in May, the eggs hatch. The parents feed their noisy hatchlings insects, berries and cactus fruit. Even after they fledge, mom and dad continue to feed and watch out for their young, sometimes caring for overlapping broods.
Only two species of birds, Gila Woodpeckers and Gilded Flickers, make cavity nests in saguaro cacti. But many others make use of these cozy and protective hidey holes, Elf Owls, American Kestrels, Ash-throated Flycatchers, European Starlings and Screech Owls to name a few.