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Row crops - corn, soybean, spring and winter wheat, cotton, sorghum, rice, peanuts, and tobacco – are dominant features of the U.S. agricultural landscape that provide valuable resources to waterbirds. In order to better understand how these crops and croplands are used by waterbird species, and how these species are impacted by row-crop production practices, a systematic review of the scientific literature was undertaken. The findings of 550 published papers, of which 350 directly involved waterbird use of crop fields in North America, are synthesized in Waterbirds on Working Lands: Literature Review and Bibliography Development.

Harvesting in Minnesota. © Jim Root

Patterns in Waterbird Use of Row Crops

As the report details, waterbird use of row crops varies greatly depending on crop type, waterbird species, and geographic region. Among row crops, more than twice as many species have been reported in rice fields than in fields planted to any other crop type. While the number of species reported on land planted to corn, sorghum, and winter or spring wheat is noteworthy, few species have been reported in cotton, peanuts, or tobacco.

The most commonly observed activity is foraging on row-crop resources during the non-breeding periods – primarily winter. However, waterbirds also use some crops – principally rice, corn, and wheat – during the breeding period for foraging and/or nesting. Among these row crops, more species have been confirmed to nest in wheat (17 species) and rice (13), than in corn (3), sorghum (2), and soybeans (1). There were no accounts of waterbirds nesting in cotton, peanuts, or tobacco.

The principal groups of waterbirds observed using fields also differs among crop types. Rice fields appear to attract a great diversity of waterbirds including waterfowl, shorebirds, wading birds, other waterbirds, and various landbirds. For the remaining cereal crops of corn, wheat, and sorghum, the primary users include waterfowl, a handful of shorebird species, an abundance of cranes, and a few species of landbirds. Soybean fields are visited by a similar array of waterbirds, but, where flooded, can also attract a great diversity of shorebirds.

In total, at least 55 percent of North American waterbird species (not including seabirds) have been documented using row crops. This percentage includes 30 waterfowl species, 30 shorebird species, 16 wading bird species, 22 other waterbird species, and 22 wetland-associated landbird species. Among those, a total of 36 species considered to be of Conservation Priority by the National Audubon Society have been documented in the following crops:

• 30 species in rice fields – and 17 solely in rice
• 11 in corn
• 11 in wheat
• 9 in sorghum
• 7 in soybean
• 3 in cotton
• 1 in peanut fields

From a geographic perspective, there is considerable variability in waterbird use of agricultural lands among the seven Bird Conservation Regions (BCRs) that have the greatest acreage in row-crop production:

• Mississippi Alluvial Valley (BCR 26): 31 species observed. 5 crops used, primarily rice and flooded soybeans. Number of species vary from 1 in corn and cotton to 23 in rice.
• Prairie Potholes (BCR 11): 18 species observed. 4 crops used, primarily wheat and corn. Number of species vary from 6 in soybeans to 16 in spring wheat.
• Central Mixed-Grass Prairie (BCR 19): 15 species observed. 4 crops used, primarily wheat and corn. Number of species vary from 5 in sorghum and soybeans to 11 in winter wheat.
• Eastern Tallgrass Prairie (BCR 22): 13 species observed. 4 crops used, primarily corn. Number of species vary from 3 in sorghum to 12 in corn.
• Shortgrass Prairie (BCR 18): 12 species observed. 5 crops used, primarily corn. Number of species vary from 1 in cotton and peanuts to 7 in corn.
• Central Hardwoods (BCR 24): 6 species observed. 3 crops used. Number of species vary from 3 in corn and winter wheat to 4 in soybeans.
• Prairie Hardwood Transition (BCR 23): 4 species observed. 3 crops used. Number of species vary from 1 in soybeans to 4 in corn.

Effects of Crop Production Methods

The literature review revealed a number of common themes across crops in how production methods impact waterbirds, including:

• practices associated with conventional tillage have been shown to have both negative and positive effects.
• in contrast, the benefits of no or reduced tillage practices far outweigh any negative impacts on waterbirds
• in rice and soybean, the use of winter flooding as a management tool clearly benefits many waterbird species
• impacts of sowing practices depend on the method and timing of planting relative to the preferences and timing of waterbird nesting in row crop fields
• there are considerable gaps in our knowledge of how crop production methods impact waterbirds

Review the report for complete discussion of these and other issues.