In the rain-starved deserts of coastal Peru, tiny patches surprisingly rich in plant life dot the landscape. Burrowing birds may be responsible, scientists say.
Mounds of sand shoveled out by nest-digging burrowing owls and miner birds harbor more seedlings and exclusive plant varieties compared with surrounding undisturbed soils, researchers from the National University of San Marcos in Lima, Peru report in the October Journal of Arid Environments. Although the mounds hold fewer seeds, the structures may provide a sheltered and moist germination environment at the start of the growing season — unlike adjacent crusty soils carpeted with cyanobacteria, lichen, moss and algae.
“The ability of seeds to germinate in the desert is a daunting task,” says Jayne Belnap, a U.S. Geological Survey ecologist based in Moab, Utah, who wasn’t involved in the study, “especially if you have a crust.”
That crust inhibits seed growth in two ways. Seeds stranded on top are exposed to the harsh environment, and may not be able to sprout at all. And the crust itself can act as a barrier for water to reach buried seeds, and for seedlings to emerge.
But when burrowing birds break the crust and dig up sand, seeds can mix into the sand, and water may pool between the tossed sand and crust, the researchers say. That allows seeds to become buried and accumulate moisture needed to germinate.
While it’s known that burrowing mammals can break compacted soils and create nutrient-rich hot spots ideal for plant establishment, this study is the first to document similar ecosystem engineering done by dryland birds.
In 2016, Maria Cristina Rengifo-Faiffer, an ecologist now at Northern Arizona University in Flagstaff, collected soils in the National Reserve of Lachay in Peru. The area lies in a part of the Atacama Desert (SN: 2/27/18) where lomas, or mist oases, exist. It rarely rains there and most plants rely on three months of winter fog to complete their life cycle.
Samples came from 61 mounds dug up by three bird species — burrowing owl (Athene cunicularia), coastal miner (Geositta peruviana) and greyish miner (G. maritima) — as well as from adjacent undisturbed areas. She watered the soil and allowed seeds to sprout in a greenhouse, using that as a proxy for how many viable seeds there were in the soils.
The bird mounds, on average, held 1,015 seeds per square meter, while the same-sized soil crust areas housed 2,740 seeds, Rengifo-Faiffer and ecologist Cesar Arana found.
But a catalog of natural germination out in the desert found that the bird-tossed soil was much more fertile than the crust: On average, 213 seedlings sprouted out of the bird mounds compared with 176 that emerged from adjacent crusty soils.
The team also found that five plant species appear exclusively in the bird-disturbed areas, including Malvaceae species. These “microhabitats” created by burrowing birds are important to maintain plant diversity, Rengifo-Faiffer says.
“To me, that’s the coolest part of this study,” Belnap says. “You’re facilitating the presence of other species by having this burrowing happen.”