CORVALLIS - Oregon State University researchers studying "overwintering" geese in the Willamette Valley have confirmed what area farmers have suspected for years. Winter grazing geese are capable of causing significant damage in valley winter wheat fields.
The study revealed winter wheat yield losses of up to 25 percent in some fields due to goose grazing.
Flocks of geese damage crops by feeding on young winter wheat plants as they emerge early in the year and begin developing. Researchers initially thought that grazed plants could recover later in the spring, but the study proved otherwise.
Borman stressed that the purpose of the study was not to estimate damage throughout the valley due to goose grazing, but to develop reliable methods farmers can use to estimate the amount of crop damage caused by geese.
"The project employed a combination of Global Positioning System (GPS) technology, aerial photography and yield monitoring systems to form an accurate picture of what happened in grazed fields examined in the study in January, March and April when the highest numbers of overwintering geese are present," said range scientist Mike Borman, OSU Department of Rangeland Resources. He and a department colleague, Doug Johnson, conducted the study along with Mounir Louhaichi, a graduate student in rangeland resources.
GPS uses satellites to produce an accurate map grid of a particular area or field. The map grid allowed researchers to identify specific sections within a field and study changes in those sections over time. The aerial photography revealed the extent of changes in crop growth over the field, and yield monitoring equipment installed on harvesting combines provided a picture of how yields fluctuated throughout the field.
In addition, the research team set up exclosures or fenced-off plots in fields.
"The exclosures were protected from goose grazing throughout the winter and provided several points of comparison with grazed areas in the fields," said Borman.
According to Borman, "ground-truthing" - the careful collection of observations by researchers walking through damaged areas - was a key component of the study.
"The aerial photography and yield monitoring only tell us what's going on in the field," Borman said. "To find the cause, you have to go in and take a look.
"In some areas of the fields, poor plant growth and low yields were due to excessive moisture," he said. "In other areas we observed clipped leaves and stalks on plants and the presence of goose droppings. This told use geese had been there and gave some indication of the numbers of birds grazing in the location."
The researchers classified the amount of grazing injury as light, moderate or heavy. They found that most of the damage occurred in April, although damage also occurred in January and March.
Overwintering geese grazing on valley farm land isn't new, but over the past two decades the numbers of Canada geese spending the winter in Oregon have shot up from 25,000 to more than 250,000.
"The dramatic increase is due, in part, to droughts over the past several years in California where Cackling Canada Geese had wintered until dry conditions made goose forage scarce," Borman explained.
Borman plans to conduct another project this winter to study methods of monitoring goose-grazing in grass seed fields in the Willamette Valley. Growers can then use these methods to document goose-caused damage to grass seed crops.
"This second part of the goose grazing study will be very important because grass seed is a dominant crop in the valley and there is a lot of interest in what we find," said Borman.
He noted that funding for the project is provided through a U.S. Fish and Wildlife Service grant.
In particular, Borman said, more study is needed on the costs of hazing geese, or scaring them away from fields that growers want to protect.
"Currently farmers use sound generating equipment, such as propane cannons, and all kinds of scarecrow-like devices to scare geese out of fields," said Borman. "But these birds are smart. It doesn't take them long to figure out whether a threat is real or not."
Control of the geese population through hunting is another option that is under consideration, Borman added.