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Rice Field Management Critical to Duck Densities

9/7/2012 at 12:00am

It is clear ducks like rice fields for the food and habitat, but scientists are still trying to figure out why the ducks seem to be attracted to some fields over others.                        
Image by Brent Birch

It is clear ducks like rice fields for the food and habitat, but scientists are still trying to figure out why the ducks seem to be attracted to some fields over others.                        

If you’ve spent more than a handful of winter days in this state’s Delta, it will come as no surprise to you that ducks like rice. They eat tons of it in the form of waste grain, the small portion of the state’s rice harvest that even the most efficient modern harvesting equipment fails to collect. Rice is raw energy in a concentrated dose, a desirable food characteristic for a creature with the soaring energy demands of flight.

But food isn’t a duck’s only attraction to rice. Flooded rice fields serve as surrogate wetlands on a landscape that has lost the vast majority of its natural wetland habitat, providing a place for ducks to rest and conserve energy in addition to myriad other life-cycle needs.

“Flooded rice fields are absolutely critical,” said Brian Davis, assistant professor of waterfowl and wetlands ecology at Mississippi State University and a former Ducks Unlimited biologist in Arkansas. “Now that I’m in Mississippi, when I drive back to Arkansas, you cross that bridge and it’s just another whole world with the amount of flooded rice.”

As ducks flock to rice fields, so do hunters. Leasing duck hunting rights on rice fields is big business in The Natural State; some sweet spots with a proven history command a lease price that some would consider obscene. Although Arkansas is rightly known for its flooded-timber duck hunting, the relative dearth of bottomland hardwood forest in comparison to Arkansas’ vast rice acreage means a lot of duck hunters shoot birds in rice paddies.

But not all rice fields are created equal. Rare is the duck hunter who hasn’t endured a slow morning in a rice field while listening to profuse gunfire emanate from a neighboring field. Only the birds know what makes one field more attractive than the next. Fortunately, however, scientists are looking for answers to explain what the ducks can’t tell us.

Slimmer Pickings

It’s no secret that there’s less waste rice available to ducks than there used to be. Scarcity starts with the efficiency of modern farm equipment, which leaves about 3 to 6 percent of the North American rice harvest in the field each year. With many newer rice varieties maturing earlier than traditional strains, the already-reduced mass of waste rice is hitting the ground earlier in the harvest season, leaving it susceptible to predation, germination and decomposition.

By the time ducks arrive in the late fall and early winter, the amount of waste rice has dropped by roughly 75 percent. For every four rice grains that hit the ground in August or September, only one remains by December. An Arkansas-based experiment conducted from 2000 to 2002 found that the average dry mass of waste rice dwindled from about 241 pounds per acre in late summer to about 70 pounds per acre by late autumn.

Experimental evidence suggests that waterfowl stop foraging and leave a rice field when the abundance of waste rice reaches a “giving up” density of about 45 pounds per acre. Based on the Arkansas study that found about 70 pounds per acre of waste rice in December, coupled with a duck’s known energy needs, that means a typical 50-acre rice field will support 1,000 ducks for about a week.

“A lot of hunters know a particular rice field, and they wonder why ducks are so unpredictable, why they were on that field one day and gone the next,” said Luke Naylor, the Arkansas Game and Fish Commission’s waterfowl program coordinator. “But when you take a step back and look at numbers like that, it suddenly makes a lot more sense. They’re on the move in search of food.”

But just because today’s fields yield less waste rice doesn’t mean they’re irrelevant to ducks.

“Obviously, the number of seeds has declined,” Naylor said. “But rice still has a high value in relation to every other crop type. I wouldn’t want us to dismiss it because there’s less out there.”

Actions Speak

Arkansas farmers planted 1.25 million acres of rice this year, by far the most rice acreage of any state, and numerous research projects carried out over the past decade shed light on the best ways to make that acreage attractive to ducks. When it comes to making one field more attractive than the next, a landowner’s or lessee’s management actions between harvest time and the end of duck season can have significant ramifications for hunting success.

The method used to manipulate rice stubble after the harvest can have consequences for wintertime duck use. More than one study has measured duck densities in fields treated with various post-harvest stubble-management strategies, including rolling, burning, mowing, disking and no treatment. Although standing stubble that isn’t treated yields the greatest abundance of waste rice, duck use of burned fields and rolled fields is substantially greater than the birds’ use of fields with standing stubble.

“Tall, dense stubble leaves the most grain, but it’s tougher for the birds to access it,” Davis said. “It’s kind of impenetrable.”

In experiments conducted between 2004 and 2006 on the roughly 3,000-acre Monsanto Farm south of Stuttgart, mallard use of rolled rice fields was five times greater than mallard use of standing stubble. Mallard densities in rolled fields were three times greater than in burned fields. Other dabbling duck densities were highest in fields with burned rice straw.

The Grand Prairie-based research concluded that “incomplete” burning of rice stubble was the best management practice for attracting ducks to harvested rice fields, with rolled stubble the second-best option. Houston Havens, the lead researcher on the project, noted that burns conserved more waste rice than other stubble-management practices and were less expensive than mechanical methods. He also pointed to burned stubble’s capacity to replicate hemi-marsh, a mix of open water and vegetation that long has been recognized by waterfowl managers as a duck’s preferred habitat on the prairie breeding grounds.

“It seems to carry over to the wintering grounds,” Naylor said. “It probably has a lot to do with accessibility, but there’s something magical to a duck about this 50/50 mix of water and vegetative cover. And there’s probably something about landing in open water that makes it more attractive; maybe it’s sort of like a safety net. There’s also escape cover and habitat for pair bonding. Pairs want to get away from other ducks as the winter goes on, and this hemi-marsh habitat may allow that.”

Flood Findings

Just as a field full of stubble is less attractive to ducks, so is a rice field without water. Flooded rice fields attract wintering ducks by filling a habitat void caused by the loss of natural wetlands. Furthermore, research dating to the mid-20th century has shown that more than 70 percent of rice placed in wetlands persists four months; by contrast, about 80 percent of soybean mass in wetlands deteriorates after three months.

The amount of flooded rice field habitat appears to play a role in a landscape’s capacity to attract ducks to individual fields. In a study from California’s Sacramento Valley, researchers found a positive relationship between duck densities and the amount of flooded rice fields inside a 3-mile range. Likewise, a California-based radio-telemetry study of pintails and white-fronted geese found positive relationships between bird movements and large-scale patterns of rice production.

Jody Pagan, general manager and chief biologist for 5 Oaks Wildlife Services in Stuttgart, recommends a staggered approach to flooding rice fields. When managing fields used by 5 Oaks Duck Lodge, Pagan floods any burned-straw rice fields as soon as the fires go out, an attempt to create habitat for early-migrating blue-winged teal and a strategy that prevents germination of waste grain. Before Halloween, he’ll flood an estimated 10 percent of the lodge’s rice fields to create additional habitat for early-migrant mallards and other dabblers. Some 25 percent of the fields will be flooded by Thanksgiving, and he’ll gradually add water to more fields as the duck season progresses through January.

“Staggered flooding is the way to go,” Pagan said. “You want to keep adding water a little at a time so you can keep making new food sources available to the ducks as they deplete other food sources. You can literally watch the ducks respond when you put that new water on the fields.”

Rest Stop

Resting rice fields during hunting season serves as a third component of habitat management. While rice fields provide foraging habitat for ducks, they also meet other life-cycle needs, including refuge areas for undisturbed rest. A southwestern Louisiana pintail study discovered that feeding comprised only 21 percent of the birds’ mean daytime activities, with resting accounting for 52 percent, comfort movements 16 percent and courtship 4 percent.

“Undisturbed rice fields are awesome,” Davis said. “Rice fields are obviously critical for adequate foraging opportunities, but they’re also critical for use as a habitat where the birds can do absolutely nothing. Flight requires an energy expenditure of 100 times a duck’s basal metabolic rate, so every time a bird is disturbed and has to get up and move, he’s expending a lot of energy. We’ve all driven through the Delta and seen ducks with their heads down feeding, but it’s almost as important to see ducks doing nothing.”

Regardless of how a duck chooses to use Arkansas’ abundant flooded rice habitat, you can’t dispute the importance of the state’s rice acreage to ducks and duck hunting. And when paired with the state’s remaining natural wetlands, it’s a habitat combination that’s hard to beat.

Tagged: 5 Oaks Duck Lodge, Arkansas rice, Grand Prairie, Trey Reid, 5 Oaks Wildlife Services, Jody Pagan, Brian Davis, duck hunting, rice

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