do not hear on an ultrasonic level, meaning that ultrasonic scarers often have little or no effect in deterring birds. Cartridge scarers Cartridge scarers include a wide variety of noise-producing cartridges usually fired from rockets or rope bangers, or on aerodromes from modified pistols or shotguns, which produce a loud bang and emit flashes of light. They include shellcrackers, screamer shells and whistling projectiles, exploding projectiles, bird bangers and flares. Bird banger cartridges commonly use a low explosive known as flash powder. Cartridges are projected from a shotgun with a range of , or pistols with a range of approximately , before exploding. Bird scaring cartridges can produce noise levels of up to 160 dB at varying ranges but in some countries both the cartridges and the gun require a firearms certificate. Pyrotechnics have proved effective in dispersing birds at airports, landfill sites, agricultural crops and aquaculture facilities. At airports in the United Kingdom, shellcrackers fired from a modified pistol are the most common means of dispersing birds, as they allow the bird controller to have some directional control over birds in flight, so they can be steered away from runways. However, as with all similar noises, there is a high risk of birds becoming used to any pyrotechnics or cartridge explosions. Benign acoustic deterrence In 2013, Dr. John Swaddle and Dr. Mark Hinders at the College of William and Mary created a new method of deterring birds using benign sounds projected by conventional and directional (parametric) speakers. The initial objectives of the technology were to displace problematic birds from airfields to reduce bird strike risks, minimize agricultural losses due to pest bird foraging, displace nuisance birds that cause extensive repair and chronic clean-up costs, and reduce bird mortality from flying into man-made structures. The sounds, referred to as a "Sonic Net," do not have to be loud and are a combination of wave forms—collectively called "colored noise"—forming non-constructive and constructive interference with how birds talk to each other. Technically, the Sonic Net technology is not a bird scarer, but discourages birds from flying into or spending time in the target area. The impact on the birds is similar to talking in a crowded room, and since they cannot understand each other they go somewhere else. Early tests at an aviary and initial field trials at a landfill and airfield indicate that the technology is effective and that birds do