WASHINGTON, D.C. – Research into the effects of cover crops on grassland birds showed that positive impacts were determined by region and life stage, according to a professor of wildlife science at the University of Tennessee, Knoxville.

The studies were a part of the Conservation Effects Assessment Project, led by the USDA’s Natural Resources Conservation Service (NRCS). Bird use of cover crops in Iowa, Tennessee and other states was studied, the agency said.

“I guess some of the take home messages here are that there’s regional differences in terms of the benefits that cover crops may provide for birds,” Dr. David Buehler explained. “And there’s also life stage specific differences in terms of the benefits they may provide.

“Generally we were seeing that during the breeding season, the use was relatively limited and the benefits were generally not seen as being positive. But at other times of the year, during the non-breeding season, both in pheasants in Kansas and non-breeding birds in Tennessee, we saw considerable use and perceived benefits.”

Buehler spoke during an April 25 NRCS conservation outcomes webinar.

In Tennessee, researchers studied a seed mix of cover crops: crimson clover, hairy vetch, Austrian winter pea, daikon radish, triticale and winter wheat. Cover crops were used in corn, soybeans and cotton.

The study documented avian use of cover crops during winter, migration stopover and nesting periods. Researchers found 66 species made visits to cover crop fields and 64 to non-cover crop fields, Buehler said.

As for single species occupancy models, he said five species – dickcissel, eastern meadowlark, field sparrow, red-winged blackbird and Savannah sparrow – “showed a possible relationship between occupancy and the presence of cover crops. If you actually looked at the occupancy rates, generally the cover crop fields had about a 5-10 percent greater occupancy than the non-cover crop fields did. This was basically a positive impact for these grassland species in terms of occupancy.

“But it’s also important to note that these values are relatively modest. Typically in Tennessee on CRP (Conservation Reserve Program) grasslands, for example, you would see occupancy rates for these species at somewhere around .75. So, even though there’s a significant effect here, the overall effect size is still fairly modest.”

The study found occupancy rates of .07 to .28 for those five species on cover crop and non-cover crop fields.

Cover crop fields showed relatively limited use by breeding birds, and the use was slightly negative, Buehler said, “because we’re encouraging some of these birds to breed when in fact the likelihood of being successful is very low.”

In the non-breeding season – winter and migration – use of cover crop fields was considerable, he said. “I generally see that as beneficial because the resources that they’re finding there seem to be sufficient to keep attracting them and hopefully supporting survival during these periods.”

In Iowa, researchers examined avian interaction with cereal rye used as a cover crop in a corn-soybean rotation, said Dr. Adam Janke, a wildlife specialist with Iowa State University Extension. Janke also spoke during the webinar.

The variation in the way cover crops are applied may impact their secondary benefits, including to wildlife, he noted. Growing conditions, cover crop species and mixes, the cash cropping system and termination methodology and timing must all be considered, Janke said.

The impact of cover crops on wildlife is something researchers are trying to understand now that their use has become more common in agriculture, he said. Researchers want to know if animals use cover crops for some element of their habitat: food, water, shelter and space. If that answer is yes, they then want to know the impact of that use on survival, reproduction and population constraints, Janke said.

He mentioned other studies, such as one in Kansas that found that pheasant broods used cover crop fields to rear their young and survive the winter. Research on breeding ducks in South Dakota showed they used cover crop fields in a corn-soybean rotation extensively.

“But their use of those fields exposed them to the equipment that was associated with the cash cropping system and led to widespread nest failure,” Janke said. “So, a negative impact.”

The Iowa study measured three outcomes related to breeding birds: bird use in fields with or without cover crops and grasslands; pheasant roadside surveys, and pheasant nesting.

Several bird species, including eastern meadowlark, field sparrow, grasshopper sparrow and upland sandpiper, were in greater relative abundance in cover crop fields than in row crop fields, Janke said. This suggests these grassland breeding birds are showing some sort of response to cover crops, he said.

Researchers found no change in pheasant abundance or index of productivity, Janke said. Low nest density was found in cover crop fields.

Most grassland breeding birds in Iowa don’t seem to be taking advantage of cover crop fields in the aggregate, he said. “There may be some winners like upland sandpipers and some losers, perhaps like meadowlarks, but that would have to be the source of additional research.”