On a typical January in the Sacramento Valley, the rice fields are ankle-deep in water – and full of birds that use them for food and shelter.
This year, however, lack of rain and limited access to allocated water has forced rice growers to leave fields dry. The result: Waterfowl are changing where and how they congregate and when they fly. South of Sacramento, in the San Joaquin Valley, scientists have seen a significant drop in the number of migratory waterfowl.
Almost all of the 550,000 acres of rice planted in the state is in the Sacramento Valley – where farmers keep rice fields flooded in the winter as much to create “surrogate wetlands” for birds as to decompose rice straw. That flooding is considered crucial to waterfowl, given that only 3 percent of the state’s historic wetlands remain, the rest displaced by farmland and urban growth. Nearly 7 million waterfowl and 300,000 shorebirds annually visit the Sacramento Valley, a key stop on the Pacific Flyway. A majority of the food they eat comes from rice fields.
“The few places that have water – they have birds,” said rice grower Tom McClellan. “But you’re not seeing a great number of birds.”
The effect of the drought is most telling in the western part of the Sacramento Valley, where McClellan farms. He has not been able to replenish his fields with water. When drought conditions take hold, the federal Bureau of Reclamation looks to rice decomposition water for additional supplies.
When that happens, as it has this year, water cannot be diverted to McClellan’s farm from the federally controlled Sacramento River. Whatever water is found on his property is water that already existed in storage drains, he said.
As a result, many of the 1,500 acres that McClellan farms in Sacramento and Sutter counties are now dry.
At one of his rice fields just north of the Sacramento International Airport, McClellan recently sampled the soil by running it through his hands. In a normal year, rain would have kept the soil moist, with most of it clumped together in clay-like blocks. McClellan pulled a current sample from a dry field. It quickly fell apart in a series of dry, granular clumps.
No birds were found on his fields aside from a stray snowy egret, although a large flock of snow geese congregated nearby in a neighbor’s unflooded field.
Studies have shown that when rice field burning was replaced with flooding in the 1990s, the change had a positive effect on waterfowl. "We saw an increase in the winter body weight of many duck species," said Greg Yarris, wildlife biologist with the Central Valley Joint Venture. “Birds that have higher weight have higher survival weights and will reproduce at higher rates come spring.”
Disease rates also plummet when weights are higher, he said.
How the drought is affecting bird populations in the Sacramento Valley is still unclear. The state Department of Fish and Wildlife is conducting its annual midwinter survey of birds in the Sacramento Valley and expects to release results in the first week of February, said Melanie Weaver, an environmental scientist with the department.
Currently, the only thing that is known for sure is that a dry spring will affect bird breeding, Weaver said. “If there is no rain going into summer – that would be bad,” said Weaver. “It doesn’t mean that ducks are going to disappear from the landscape. We’ve had drought cycles before and they’ve gone through that.”
“But less water means that hens do not have an area to take their broods, or ducklings,” she said. “They don’t have a safe place to molt.”
Male and females, after going through a nesting cycle, require bodies of water for molting. The water keeps them safe from land predators and also offers food.
A reduction in the number of flooded rice fields means birds also take to congregating in tighter geographic spaces wherever water can be found. This leads to overcrowding in some areas, and the outbreak of avian diseases such as avian cholera, Weaver said.
The effect of the drought on bird populations is a little clearer in the northern San Joaquin Valley. A recent midwinter bird survey conducted in early January between Mendota and Modesto found a significant drop in the number of birds, said Cristen Langner, wildlife biologist with Fish and Wildlife.
The survey counted 450,961 waterfowl in January. That compares with 626,276 birds in 2013 and 1.2 million in 2012.
Langner said the survey, conducted from an airplane flying 100 feet from ground, found that birds were not in their usual locations for this time of year. It’s possible, she said, that they’re simply not making it as far south as Mendota.
“This is a perfect-storm kind of thing,” Langner said. “We’re not getting the weather, we’re not getting the water, and we’re not getting the birds, either.”