not habituate to the sound. The provisional and full patents were filed in 2013 and 2014 respectively, with further research and commercialization of the technology being ongoing. Other Humans Historically, humans have been employed to scare birds from crops, using a variety of deterrents including throwing stones, flashing with mirrors, or operating noise devices. This is only cost-effective where the cost of labour is sufficiently low relative to agricultural profit margins. In Victorian England, children were employed to do this job. In the Huleh Valley in Northern Israel, rural labourers, primarily Arabs and Druze, use USVs and multiple devices to keep common cranes off high-value crops. Dogs The control of birds and other wildlife such as deer through harassment by trained border collies has been used at aerodromes, golf courses and agricultural land. The dogs represent an actual threat, and so elicit flight reactions. Habituation is unlikely as they can continually pursue and change their behaviour. Border collies are used as they are working dogs bred to herd animals and to avoid attack, and they respond well to whistle and verbal commands. A single border collie and its handler can keep an area of approximately 50 square kilometres (19.3 square miles, 4998.7 hectares, or 12,179.2 acres) free of larger birds and wildlife. However, although they are effective at deterring ground foraging birds such as waders and wildfowl, they are not so useful for species that spend most of their time flying or perching, such as raptors and swallows. In 1999, Southwest Florida International Airport became the first commercial airport in the world to employ a border collie in an airfield wildlife control programme. After the use of the collie, numbers and species of birds on the airport declined and most birds that remained congregated in a drainage ditch away from the runway. The number of bird strikes dropped to zero compared to 13 for the same period the previous year. Several other airports and airbases have now started similar programmes. At Dover Air Force Base, Delaware, bird strike damage to aircraft caused by birds has been reduced from an average of US$600,000 per year for the proceeding two years to US$24,000 per year after the initiation of a bird control programme that included the use of border collies. Predators Using predators as a natural bird deterrent has become a recommended form of controlling bird infestations. Specially selected species are trained