Flora and Fauna News

Saguaros to the Rescue!

By Michael Plagens
Sonoran Desert Sciences

PHOENIX, Az. -----This is Summer Solstice time in the Sonoran Desert. Within the next several weeks or so we should reach our highest temperature of the year. For many desert animals, moisture and food supplies have reached a critical level; many will perish. But for others the Saguaro Cactus (Carnegiea gigantea) comes to the rescue at this most perilous time with a bounty of red, ripe, juicy fruit. Dozens of fruit are clustered at the tops of the saguaro arms with a few splitting open each day. To the casual observer they might appear to be bright red flowers in that they are usually five-pointed.

White-winged Doves, Gila Woodpeckers, thrashers, and even Cactus Wrens gorge themselves once the tough cortex splits open. Some of the fruits eventually get knocked loose and fall to the ground where Kangaroo Rats, Pocket Mice, Javelina, Coyotes, ground squirrels and Gopher Tortoises among others eagerly await. Aphaenogaster, Pogonomyrmex, and Forelius ants swarm any untended fruit. Tiny nymphs of the Leaf Footed Bug, Leptoglossus zonatus, depend on the exposed seeds for their initial development; they could never reach the seeds through the thick walls of the cortex (peel).

Each fruit contains hundreds of tiny black seeds so that many escape the multitudes of birds, insects, reptiles and mammals that eat them. Those that pass through the guts of doves might still be viable. In any case many seeds will be ready when the summer rains arrive in force in the next few weeks. The seeds are labile, that is they must germinate quickly or perish. In order for a seed to germinate, survive and grow into a new saguaro requires an incredible string of fortuitous events. Needless to say the vast majority never make it. Years with conditions suitable for saguaro regeneration are infrequent ... sometimes a dozen years will pass before a new generation can take hold. But eventually a new cactus will grow tall and bear new fruit for future generations of Sonoran Desert animals.

White-winged Doves on a fruiting
Saguaro Cactus by Mike Plagens