Have you ever heard of a scarecrow? Frightening techniques are often used for controlling crop damage and dispersing roosts. There are a wide variety of frightening devices available including propane cannons, pyrotechnics (shell crackers and screamers) and other noise makers, such as clappers, motion-activated alarms and sprinklers, and distress alarm call systems. Be sure to check local noise ordinances to determine if pyrotechnic & other noise-making devices are permitted in your area. Use pyrotechnic devices with caution, as sparks they generate are capable of starting grass fires.
Habituation
Habituation is when an animal gets used to the same stimulus and stops responding. You should move stationary frightening devises to prevent habituation. Crows are “smarter than the average bird” and will quickly learn that stationary objects (including the speakers which deliver distress alarm calls) do not pose a threat.
Ultrasonic noisemakers
Various wildlife control supply companies recommend ultrasonic noisemakers as a solution in repelling many species of birds. Buyers beware! Research indicates that many birds do not respond to these devices and may not even be able to hear sounds in the ultrasonic range. Before you buy one of these devices, you may want to rent it first.
Dead crow effigies
Carcasses, taxidermic or artificial, can be used as frightening devices in both preventing crop damage and in roost dispersal. Studies indicate that crows respond to effigies with alarm, especially when used in conjunction with other frightening techniques.
To prevent crop damage, dead crow effigies should be hung throughout the area to be protected. In addition, posing them in an unnatural position on the ground may also be beneficial in that they can be seen by birds flying above. As with any frightening device, they would need to be moved frequently to prevent acclimation. When used to disperse communal roosts, effigies should be hung throughout the perching areas. It is important that the roost is lighted so that the birds can see the effigies.
Lasers
Lasers can be used to disperse communal nighttime roosts, but only if they are used in conjunction with additional frightening techniques. Research indicates that when used alone, lasers will cause the birds to disperse for a short period of time (usually returning the same night), but will not cause them to abandon the roost. They should be used with great caution due to the potential dangers associated with them. Follow all of the manufacturer’s instructions and cautionary warnings.