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Fall Canada goose (Branta canadensis) counts at Horicon National Wildlife Refuge reached 100,000 in the early 1960s and were increasing annually. Management agencies dumped 467.5 tons (475,003 kg) of shelled corn to hold Canada geese on the refuge in 1965, but crop depredations were high nevertheless. In 1966, an effort was made to disperse Canada geese with aircraft, but the program failed due to lack of cooperation. In late October a helicopter operated only over the refuge flushed geese from adjacent private lands up to 2 km (1.24 mi) distant. Airboats were effective and versatile for hazing Canada geese because they could be operated after dark. While Canada geese were highly sensitive to helicopters flying low, they could not be used after dark. Although Canada geese loafed in uplands during the day, thousands returned during the 2-hours after sunset in 1966. Disruption of night roosting was achieved with airboats in 1976-78. Propane exploders were largely ineffective, but frequent use of airboats for exploder maintenance provided a major disturbance.