Birds Prefer Natural Wetlands to Water-Soaked Rice Fields
When wading birds have a choice between flooded rice fields or natural wetlands, they choose to roost and forage on nature’s turf, according to a new study published this week in the journal The Condor: Ornithological Applications.
Study coauthor Jason Fidorra, a biologist with the Washington Department of Fish and Wildlife, said the findings show rice fields might not be the ecological havens farmers have claimed.
“Maybe rice fields to some extent can support wildlife and birds, but that shouldn’t be the conservation goal,” he said. “We shouldn’t count out the need to conserve and restore this natural wetland system that birds prefer.”
Fidorra was a University of Florida researcher when he led the study, which monitored habitat use of great egrets, a large wading bird with white feathers and black legs found throughout the United States.
The team caught the wild birds “by basically inventing our own Nerf-inspired net gun out of Home Depot parts,” Fidorra said, then strapped GPS sensors onto the birds’ backs to track their movements.
The sensors sent two signals daily: once in the morning while the birds were foraging for food, and once at night when they had returned to their nests.
This location data allowed the team to map when the birds were using natural wetlands and when they were on the region’s man-made ponds, crawfish ponds, rice fields, and other “human-influenced” wetlands.
The positioning data showed that the birds foraged in natural wetlands more often.
“The natural landscapes offer more diversity in terms of foraging structure,” Fidorra said. In an untouched wetland the water depths vary, allowing prey fish to gather in certain spots. Natural wetlands also offer more variety to birds, with ideal foraging conditions shifting depending on the species doing the fishing, the season, and the time of day, down to the hour.
“Compare that to a rice field, where the landscape is nearly laser-level flat,” Fidorra said. “It’s almost a homogeneous monoculture, so the diversity of prey, vegetative structure, and water depths are all highly controlled.”
So, while rice fields might provide the egrets with a “sweet spot”—a short period of each day when all the elements of water depth, prey species abundance, and rice length line up to optimize feeding—the diversity of natural wetlands allows for a much longer window of productive foraging time.
The research team chose to study great egrets in Louisiana and South Carolina, because both states contain a mix of natural and human-influenced wetland options for birds.
In California’s Central Valley, by comparison, 95 percent of the state’s historic wetlands—crucial resting and feeding habitat for millions of bird that migrate along the Pacific Flyway from North to South America every year—have been replaced by development, irrigated farmland, and flooded rice fields.
In the midst of the state’s record-breaking drought, California’s rice farmers have been under scrutiny, for their drenched fields, but have defended their water-intensive crop as “unparalleled wildlife habitat to nearly 230 species,” according to the California Rice Commission’s website.
“It’s true, these rice fields are supporting potentially the entire population of birds in spots like California’s Central Valley, France, and Italy, but that’s because they don’t have any other options,” Fidorra said. “When they have a choice, they choose natural wetlands.”