Frightening is effective in dispersing crows from roosts, some crops, and other troublesome sites. In a recent study in California, crows were successfully dispersed from urban crow roosts using tape-recorded “squalling” calls (given by a crow struggling to escape from a predator) and a portable tape player commonly used by hunters to attract animals. Such dispersal allows crows to be moved from problem sites to sites where they are less likely to interfere with people.

In addition to recorded distress or alarm calls, frightening devices include gas-operated exploders, battery-operated alarms, pyrotechnics (shellcrackers, bird bombs), chemical frightening agents (see Avitrol® below), lights (for roosting sites at night), bright objects, clapper devices, and various other noisemakers. Beating on tin sheets or barrels with clubs can help in scaring birds. Spraying birds as they land, with water from a hose or from sprinklers mounted in the roost trees, has helped in some situations. Hanging mylar tape in roost trees may be helpful in urban areas.

A combination of several scare techniques used together works better than a single technique used alone. Vary the location, intensity, and types of scare devices to improve their effectiveness. Supplement frightening techniques with shotguns, where permitted, to improve their effectiveness in dispersing crows. Ultrasonic (high frequency, above 20 kHz) sounds are not effective in frightening crows and most other birds because, like humans, they do not hear these sounds. For a more detailed discussion of frightening techniques, see "Bird Dispersal Techniques" at the following Web site: http://icwdm.org/handbook/birds/Dispersal.asp.
Animated “crow-killing” owl models can frighten crows from gardens and small fields. These are made from a plastic owl model with a crow model attached in such a way that the crow appears to be in the owl’s talons. Movement is supplied by mounting the model on a weather vane and by adding wind- or battery-powered wings to the crow.

Clapper devices (Tomko Timer-Clapper) have been reported by the Nebraska Game and Parks Commission as successful in dispersing crows from waterfowl concentration areas where crow roosting was destroying a multiple-row shelterbelt and where there was concern that crows were aggravating the spread of avian cholera. A clapper device intermittently “claps,” producing a sound much like a twig snapping or like two boards clapping together. The device can be placed up in trees or at other sites close to crow perches, making it perhaps more significant to crows as a frightening device. Clappers have also been used to frighten and disperse other birds (starlings, grackles, swallows) and to repel deer at night. Like many other frightening techniques, clappers appear to be most effective with wary populations. Populations that have habituated to people or disturbance to such an extent that they have lost their wariness may not respond.

Avitrol®
Avitrol® (active ingredient: 4-aminopyridine) is a Restricted Use Pesticide and chemical frightening agent, available in a whole-corn bait formulation (Double Strength Whole Corn) for use in dispersing crows. It is only for sale to certified applicators or persons under their direct supervision and only for those uses covered by the applicator’s certification.

Avitrol® baits contain a small number of treated grains mixed with many others that are untreated. Birds that eat the treated portion of the bait behave erratically and/or give warning cries that frighten other birds from the area. Generally, birds that eat the treated particles die. Overall, because of the type of damage problems associated with crows, Avitrol® is unlikely to be used often. This product is included here, however, because situations may arise in which its use would be helpful. Before using this product for crow control, it is best to contact a qualified person trained in bird control work (someone from the Cooperative Extension or USDA-APHIS-Animal Damage Control, for example) for technical assistance. For additional information on Avitrol®, see "Blackbirds" and "European Starlings" at the following Web sites:
"Blackbirds" http://icwdm.org/handbook/birds/bird_e25.pdf

"European Starlings" http://icwdm.org/handbook/birds/EuropeanStarlings.asp.

Resources: (online)
Crows