Effects of mowing on breeding bird abundance and species composition in alfalfa fields: B.J. Frawley & L.B. Best, Wildlife Society Bulletin, 19(2), 1991, pp 135–142

Abstract

Alfalfa (Medicago sativa) is an important forage plant for livestock because of its high nutritional value (Barnes and Gordon 1972). Most of the 11 million ha of alfalfa grown annually in the U.S. is harvested in the northcentral states (Barnes and Sheaffer 1985). An average of 610,000 ha of alfalfa was harvested each year in Iowa during 1986-1987 (Iowa Dep. Agric. and Land Stewardship, unpubl. data). Birds nesting in alfalfa fields encounter events unique to hayfields. In the spring, the vegetation develops from short and sparse to tall and dense. At the first mowing, the field's vegetation is reduced to 7to 10-cm tall stubble (Barnes and Sheaffer 1985), causing regrowth. This cycle usually occurs 3 times during the growing season (April through September). Thus, mowing frequently changes the amount and structure of vegetation available to birds and may affect bird densities. Mowing also destroys nests, eggs, and adult birds. Despite the potential effects of mowings, little research has been directed at how nongame birds respond to the removal of vegetation and the subsequent regrowth (see Harrison 1974, Bollinger et al. 1990). Several bird species commonly nesting in hayfields have declined recently, including eastern (Sturnella magna) and western (S. neglecta) meadowlarks, dickcissels (Spiza americana), and grasshopper sparrows (Ammodramus savannarum) (Robbins et al. 1986). Warner and Etter (1989) and Bollinger et al. (1990) implicated mowing as a partial reason