Evaluation of avian use of agricultural cover crops during the winter, migration stopover, and the breeding season in Tennessee

The U.S. Department of Agriculture Natural Resources Conservation Service administers the cover crop program to provide technical and financial assistance to agricultural producers to sow herbaceous plant seeds to establish cover crops to protect agricultural fields from soil erosion during the non-growing season (late fall through spring). Soil retention and water quality benefits have been documented, but potential benefits for avian wildlife remain largely unknown. I used line-transect avian and vegetation surveys to examine use of cover crop fields by birds during the non-breeding period (winter), migration, and the breeding season. I compared avian use of cover crop fields with no-till row-crop fields without cover crops (controls). Analyses of variance (ANOVA) were used to compare vegetation parameters by season, year, and enrollment type. I modeled single species occupancy for focal species, multispecies richness, cumulative avian conservation scores from Partners in Flight, and calculated species accumulation curves to compare avian use of cover crop and control fields.

Overall, implementation of the cover crop practice was successful in that >80% of the fields had >75% cover in cover crops by spring in 2021 and 2022. Based on the ANOVAs, cover crop fields had greater percent vegetated cover, and lesser percent bare ground than control fields. Six of the fourteen focal species occupancy models showed a relationship between occupancy and field type, with five of the six preferring cover crops over control fields. A large diversity of avian species was detected using cover crop fields (n = 70). However, confidence intervals in species accumulation curves overlapped, suggesting that cover crop and control fields would be used by a similar number of species if survey effort was equal. Species richness and cumulative conservation score per transect were about 10% greater in cover crop fields than in control fields. I documented limited breeding activity in cover crop fields early in the breeding season in April, suggesting that some birds were attempting to breed prior to cover crop termination and subsequent planting. However, given the timing of this breeding activity, it is unlikely that cover crop fields provided a significant resource for avian nesting cover.