Breeding waterfowl populations have suffered a 19 percent drop in the Sacramento Valley this year and a steeper decline statewide due to the drought and poor habitat conditions, according to the latest annual survey released by the California Department of Fish and Wildlife.
A lack of precipitation has dried up wetlands, forced farmers to fallow rice fields and reduced food sources available to waterfowl in California. The survey, conducted by aircraft over prime nesting areas in the Central Valley and northeastern California, estimated 315,580 breeding ducks in 2015, a nearly 30 percent drop from the 448,750 last year.
“We expect the breeding populations to continue to decline until habitat conditions improve,” said Melanie Weaver, wildlife biologist with the CDFW.
The steepest declines were found in the northeast part of the state, where populations declined by 40 percent, Weaver said. California’s most common duck species, breeding mallards, fell by 27 percent.
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Similar declines have occurred in the past, but breeding duck populations recovered after habitat conditions improved, Weaver said. With California in its fourth year of drought, any recovery will take time.
“We’re not expecting a rebound next year even if we do get improved habitat conditions,” she said, noting that recovery typically takes three years.
Breeding population numbers for all waterfowl have been dropping since 2007, according to the CDFW.
“When you think of these population drops cumulatively, that’s a pretty big impact on local waterfowl bird populations,” said Meghan Hertel, program director with Audubon California. “It really shows that the drought is hitting our wetlands – and hitting them hard.”
Hertel said refuges like Sacramento National Wildlife Refuge and Delevan National Wildlife Refuge, as well as state wildlife areas, typically irrigate land in the summer.
“Last year, many of those refuges chose to do little or no irrigation, resulting in few spring and summer wetlands,” Hertel said. “When you don’t irrigate one year in a wetland, you reduce the number of seeds in that wetland that allows crops to grow in a subsequent year and the food base keeps getting reduced.”
Another problem arises when dry wetlands evolve into something else as a result of drought or lack of irrigation.
“You lose the plants and the design of the wetland itself, so when you go to reuse that wetland, you have to do quite bit of restoration work to get it back to a wetland state,” Hertel said.
About 4 million birds fly into the Central Valley in the fall and winter as part of their annual migration along the Pacific Flyway.
Rice fields represent one key type of shrinking wetland. Typically, rice farmers leave fields flooded after fall harvest to serve as surrogate wetlands for migratory birds and waterfowl.
The drought has curtailed rice cultivation, especially in the Sacramento Valley, where almost all of the rice is grown in California. Last year, 434,000 acres of rice were planted statewide compared to 567,000 in 2013, according to the California Rice Commission.
Fewer wetlands also concentrate birds in remaining watering holes. That can more easily lead to transmission of diseases like avian botulism and cholera.