Few studies have measured the impacts of mowing on bird use of habitat and the risk of bird collisions with aircraft on North American airfields. The need for this research has increased as airfields become some of the only large contiguous grasslands available to rare migratory birds in some areas. I studied bird abundance, distribution and behaviors at Westover Air Reserve Base, Massachusetts, USA in June and July 2004. I compared my data with bird strike records to discern any patterns associated with mowing of airfield vegetation. There was no difference in total number of birds or species between mowed and unmowed plots adjacent to runways and taxiways. There were more Upland Sandpipers and Eastern Meadowlarks in mowed vegetation and more sparrows (Grasshopper and Savannah) in unmowed vegetation. From 1997 to 2005, swallows were the birds most often struck by aircraft in June and July at Westover, and were also the second most numerous birds in both mowed and unmowed plots. Bird species that pose high Bird/Wildlife Aircraft Strike Hazard (BASH) risk at Westover included Turkey Vulture, Red-tailed Hawk, Great Blue Heron, and Canada Goose. I did not observe those species in paired plots of mowed or unmowed airfield vegetation adjacent to runways and taxiways at Westover. I opportunistically observed 64 incidents where species that pose high BASH risk were in or adjacent to areas where aircraft operate. Birds struck most frequently at Westover between April 1997 and January 2005 were “swallows”, American Kestrel, Killdeer, Horned Lark, Eastern Meadowlark, and Mourning Dove. Current mowing practices at Westover may have adverse effects on Upland Sandpiper and Grasshopper Sparrow, both state-listed, rare, grassland birds, but may not measurably reduce overall risk to aircraft, given the continued presence of large, high BASH risk species. I recommend methods to reduce threats posed by high-risk species at Westover, and further research to seek ways to reduce adverse effects of mowing on state-listed, rare, migratory species of birds.