A Bold Bet to Ensure the Future of Desert Birds: Plant Thousands of Cacti

Earlier this year, a dozen volunteers and staff armed with trowels kicked off an urgent experiment in cactus conservation. On a clear March morning they spread out within the high-quality habitat of Tucson Audubon’s Mason Center, pushing wheel-barrows loaded with three- to six-inch cacti. By noon, they had planted 130 saguaros near ironwood, mesquite, and palo verde “nurse trees,” which provide shade and boost the baby cacti’s chances of survival.

If the succulents take root, they have a long way to grow. They won’t start flowering until they are 35 to 70 years old, and it can take up to 100 years for their first branching arms to extend. In more time, mature cacti may reach taller than 40 feet. That’s when Desert Purple Martins tend to make them home, moving into cavities previously hammered out by woodpeckers. There, the graceful swallows raise chicks safe from the Sonoran Desert’s sweltering sun.

However, climate change is pushing saguaro cactus populations to the edge and putting the entire ecosystem at risk. Already a prolonged drought of nearly 30 years has hit the region, reducing the survival rates of seedlings. At the same time wildfires, worsened by the heat of a warming planet and the tinder of invasive plants, have scorched and killed hundreds of thousands of mature cacti. “Even without fires, saguaros are facing a more difficult time now than they have for the last probably 10,000 years,” says Jonathan Horst, director of conservation and research at Tucson Audubon. This summer, a record-breaking heat wave has withered and even toppled cacti in the region.

The towering succulents are the defining plant of the Sonoran Desert and a key source of food and shelter, supporting more than 100 species. Gila Woodpeckers and Gilded Flickers carve out nest cavities in them, which are later used by Desert Purple Martins, Elf Owls, the federally threatened Cactus Ferruginous Pygmy-Owls, and a number of other species. Crested Caracaras and Harris’s Hawks also build platform nests atop the cacti’s spiny arms. Bats feast on cactus fruits and, along with bees, pollinate their flowers. Saguaros are also an important resource for the Tohono O’odham Nation, who make syrup and wine from its fruits.

In other words, stewarding Sonoran life means nurturing cacti, Horst says. “As an organization that tries not to myopically focus on only birds, but on all of our rich regional biodiversity, there’s just no way not to start devoting time and effort to addressing long-term saguaro declines.” As the monsoon season began this summer, when they hoped wet conditions would be ideal, the team was preparing to plant several hundred more cacti. Next year the project will expand to other reserves and parks, and over three years the chapter and its partners want to put a total of 14,000 plants in the ground.

Horst acknowledges that the plantings might not have an exceptionally high success rate, but he’s cautiously optimistic. “Nobody has tried planting lots and lots of saguaros out into a wildland context,” he says. “To some degree, what we’re doing is experimental.” The baby cacti must contend with the same droughts that have held back their wild counterparts. To establish themselves, saguaros require a particular seasonal pattern: moderate temperatures and reliable monsoon rains, followed by a wet winter, and then capped by another wet monsoon season—a set of circumstances that historically occurs about once every 10 years. But these perfect conditions haven’t happened in the region for three decades.

“In any field experiment like this, there is a certain amount of luck involved,” says Don Swann, a biologist at Saguaro National Park. “You only get saguaros when the conditions are just right.”

As these cacti mature, they’ll then have to cope with a new threat. In the past, wildfires burned in the Sonoran Desert only about once every 500 years. But many have occurred in the past few years, driven by climate change and the spread of invasive species. Because of their structure and density, flammable invasive grasses feed flames that can burn at 1,500 degrees Fahrenheit, too hot for saguaros. “The [cacti] don’t have any ability to regenerate or regrow post-fire,” says Tony Figueroa, invasive plant program manager for Tucson Audubon. “If they get burnt out, they’re dead and gone, and they’re not coming back.”

The project staff and volunteers do what they can to give each plant the best shot at survival. Tucson Audubon buys young saguaros from nurseries only after the succulents grow protective spines and are big enough to withstand minor freezes, at around age two. They also plant them strategically, near the nurse trees. Other work is underway to clear invasive grasses that fuel fires.

The long-term effort will outlast today’s participants if all goes well. Certainly they won’t live to see Desert Purple Martins benefit, as the birds won’t find the cacti suitable housing for another hundred years. To help birds in the meantime, Tucson Audubon is investigating nest boxes as well. Desert Purple Martins can’t use the condos frequented by their cousins in the eastern United States; the inside of the structures gets too hot in the desert. So, this past winter Tucson Audubon and partners held an international contest to solicit nest-box designs that resemble a cactus cavity and can also keep the birds cool. Over the summer the team installed prototypes of three winning designs to find out which the birds prefer.

When testing ends, the birds’ favored dwelling style will be used in conjunction with planting efforts to increase nest sites in areas lacking mature cacti. If Tucson Audubon succeeds, they could help sustain their local subspecies through the next century. That way, when the newly planted saguaros are all grown up, there will be Desert Purple Martins ready to move in.