Saturday, July 15, 2023

Gila Woodpeckers in Saguaro Boots

On the 7th of May, a friend visited with her family to look for nests in Saguaros. Tucson Audubon had offered some kind of sponsorship reward for finding those. So we looked at Raptor nests, a White-winged Dove, House Sparrows. The dad of the family heard fine chirps from above: deep inside the stem of a saguaro a clutch of Gila Woodpeckers had just hatched. Gila Woodpeckers and Gilded Flickers hammer holes deep into the stem or a big arm of our giant cacti. This nesting cavity is not used in the year when it's built. But soon the cactus encloses the cavity with heavy sclerotized layer of scar tissue. So now there is this hard, inverted bag hanging inside the cactus, reaching in, then curving down, as big as a boot. It is surrounded by the moist, water-storing tissue of the cactus and parts of the wooden saguaro skeleton. It's impenetrable to most predators. Most importantly, it's isolated from temperature fluctuations by the huge amount of water-holding material around it. Desert nights can be cold, daytime temperatures are extremely hot. Eldon Braun of the UoA found in his master-thesis research that the daily fluctuations inside of several Gila Woodpecker nests never exceeded 14C, even if the nights hovered around 10C and the daytime high was way over 40C (scientists use Celsius measurements). Great conditions for the woodpecker brood to grow up in. At the same time young dove chicks in their flimsy nests nearby experienced the full impact of heat and cold. Surprisingly, most dove nests produce fledglings anyway. But not surprisingly, the baby doves develop very quickly (high protein crop milk helps) and then they are out of the nest. Precocious quail chicks run from their ground nests even faster - on the day of hatching! However, the Gila Woodpeckers that we heard chirping faintly on the 7th of May are still in their 'Saguaro boot' today on the 15th of July! Now their chirping is not faint anymore, but loud and demanding! They are probably close to fledging, but still holding out. Who would be eager to leave the climatized safety of the inside of a huge cactus column for the punishing heat that the outside desert is experiencing right now? But when they do decide to fledge, monsoon rains will hopefully be right around the corner to cause scores of insects to emerge that the young woodpeckers will devour. Still, the juveniles also learn very quickly to get refreshments from our hummingbird feeders. Soon!

No comments:

Post a Comment