Overview of Damage Prevention
and Control Methods
- Removal and modification of roost trees
- Secure trash cans and dumpsters
- Remove carrion
- Alternate foods – broadcast cracked corn through fields to protect newly planted corn
- Nets and wires over high-value crops or small areas
- Cover ears of corn with paper cups or sacks after silk has turned brown
- Lines or wires spaced at 8 feet around sites needing protection – further study is needed
- Mylar® tape and effigies
- Noise-makers, pyrotechnics, and distress calls
- LRAD — Long Range Acoustic Device
- Methyl anthranilate
- DRC-1339 for use by USDA-APHIS-Wildlife Services (WS) personnel
- Shotgun – 12-gauge with No. 6 shot
- Rifle – .22-caliber rifle or air rifle
- Australian crow decoy traps
- Cage traps – minimum size 60 x 23 x 26 inches
- Pole traps – Nos. 0 or 1 padded foothold traps
Other Control Methods
- Cannon nets
- Alpha chloralose (ravens only) for use by WS personnel
Damage Prevention and Control Methods
Integrated Pest Management
Timing, Economics, and Methods
Control crows before they become habituated to a location. Populations can grow quickly when food and cover are plentiful.
In dense cedar thickets, bulldoze strips through the roost site to remove ⅓ of the habitat. This has been successful in controlling crows, but the disturbance may be hazardous to human health if soils harbor histoplasmosis spores. Vegetation management has effectively dispersed starling and blackbird roosts, andare likely effective for dispersing crows. Roosts usually occur in dense stands of young trees. Thin up to ⅓ of the branches of specific roost trees or thin trees from dense groves, to reduce the availability of perches and open the trees to weather (Fig. 5).
Secure trash cans, dumpsters, and transfer stations to prevent access to food and wastes. Remove carrion as quickly as possible and dispose of it by deep burial or incineration. Some reports indicate that providing alternate sources of food will reduce damage to crops, such as broadcast cracked corn, preferably softened by water, through a field where crows are damaging newly planted seedlings. Although this technique is helpful in some situations, it has not been thoroughly tested.
Exclusion, generally, is not practical for controlling crows, but may be useful in some situations. Nylon or plastic nets might be useful for excluding crows from high-value fruit or vegetable crops or small areas.
Stretch cord or fine wire across a field at heights of 6 to 8 feet above ground to protect crops from crows. Strips of aluminum or cloth, or aluminum pie pans may be tied to the wires, but have variable results. Lines appear to represent an obstacle that is difficult for a flying bird to see, especially when rapid escape may be necessary. Species of birds respond differently to lines, and adult birds generally are more repelled by lines than juveniles are. Other factors, such as season, bird activity, type of lines or wires, spacing, and height need further research and development.
Protect ripening corn in small gardens by placing a paper cup or sack over each ear after the silk has turned brown. The dried, brown silk indicates that the ear has been pollinated, a necessary step in the development of corn grain.
Frightening devices can be effective for dispersing crows from roosts, crops, and other sites. A combination of several frightening techniques used together may work better than a single technique. Vary the location, intensity, and types of frightening devices to improve their effectiveness. Supplement frightening techniques with lethal control, where permitted, to improve effectiveness. The addition of lethal control only has a short-term effect on the behavior of remaining birds. Ultrasonic sounds (high frequency, above 20 kHz) are not effective in frightening crows and most other birds. Strips of Mylar® tape hung in roost trees may be helpful in urban areas.
Effigies can frighten crows from gardens and small fields. Effigies may be immobile (Figure 6) or animated, and animated models are often more effective. One of the animated effigies is a “crow-killing” model, made from a plastic owl model with a crow model attached in the talons of the owl. Movement is generated by mounting the model on a weather vane, and by adding wind or battery-powered wings to the crow.
Lasers may cause crows to flee a roost, but their quick return, even after repeated treatments, suggests that lasers are not effective as a long-term technique. Crows can be dispersed from urban roosts using pre-recorded crow distress calls broadcast from a portable player.
Clapper devices that produce an intermittent “clap” can be placed in trees or at other sites close to crow perches. As with other frightening techniques, clappers appear to be most effective with wary populations. Crows that have habituated to people or disturbances may not respond. Beat on tin sheets or barrels with clubs to scare birds. Spray crows with water from a hose, or from sprinklers mounted in the roost trees as they land to disperse roosts in some situations.
Other frightening devices include gas-operated exploders, battery-operated alarms, and pyrotechnics (shell crackers and bird bombs). Various crow distress calls can be quite effective at dispersing roosts. Endeavor to present the sound before the flock lands at the roost.
Long Range Acoustic Devices (LRAD) project a high decibel sound up to 153 dB at 200 to 300 yards. The LRAD may be useful for hazing birds out of trees or off surfaces. Check local noise ordinances in urban areas before using LRADs.
Avitrol® (4-aminopyridine) is a Restricted Use Pesticide and chemical frightening agent, available in a whole-corn bait formulation for use in the dispersal of crows. It is only for sale to certified applicators or persons under their direct supervision. Avitrol® bait contains a few treated grains mixed with many others that are untreated. Birds that eat the treated grains behave erratically, give warning cries that frighten other birds from the area, and eventually die. Before using Avitrol® for the control of crows, contact a qualified person trained in the control of birds for technical assistance. Always check the label before administrating a pesticide. Avitrol® cannot be used in many urban areas.
Methyl anthranilate is a grape-flavored food additive that also is a repellent for birds in high concentrations. In aerosol form, it irritates the nasal passages of birds causing them to flee the treated area. Foggers and ultra-low volume devices are used to apply the product and disperse roosting birds.
Tactile repellents made of polybutene are available to repel crows from roosts. Avoid applying the product directly to structural surfaces: place tape or other removable material on the surface first. Polybutenes collect dust and lose effectiveness over time. They are most useful for indoor applications to repel birds.
No toxicants are registered for controlling crows. Special Local Needs 24(c) registrations have been sought for DRC-1339 (3-chloro p-toluidine hydrochloride) by WS for limited, small-scale use.
Crows are protected by the Migratory Bird Treaty Act. The USDI-Fish and Wildlife Service (USFWS) and state wildlife agencies may issue permits to shoot crows. Check your local regulations before shooting crows. Twelve-gauge shotguns set at full choke with No. 6 shot works well within 40 yards. Otherwise, use a .22-caliber rifle. Air rifles (.22-caliber or high velocity .177-caliber) are effective on perching crows within shotgun range.
The shooting of crows is more effective as a dispersal technique than as a way to reduce numbers, as crows are difficult to shoot during the day. They may be attracted to a concealed shooter by using decoys or calls of crows, or by placing a decoy (Figure 6) in a conspicuous location. In general, the number of crows killed by shooting is small in relation to the numbers involved in damage or nuisance behavior. However, shooting can help to supplement and reinforce other techniques when the goal is to frighten and disperse crows rather than reduce numbers.
Crow hunting during open seasons can be effective in rural areas. The effectiveness varies depending on movements of crows, the season in which the damage occurs, and other factors. Crows tend to be more wary of people when they are hunted and thus more easily dispersed from roosts or other areas. Further study is needed to better understand the relationships between hunting and wariness, and whether a pattern exists that might be used to improve management of crows.
Crows are protected by the Migratory Bird Treaty Act. The USFWS and state wildlife agencies may issue permits to trap crows. Check your local regulations before trapping crows. Trapping often is less useful than other techniques because of the wide-ranging movements of crows, the time necessary to manage traps, and the number of crows that can be captured compared to the total number in the area. Use of traps can be successful at locations where a small, resident population is causing damage, or where other techniques cannot be used. Situations where trapping may be cost-effective include protecting a high-value crop or large numbers of nesting waterfowl. Crows are wary and often very difficult to trap.
The Australian crow trap, a decoy trap, can be used for crows (Figure 7). It is most successful if used during the winter when food is scarce. The traps should be at least 8 to 10 square feet and 5 to 6 feet high. If desired, construct the sides and top in panels separately to facilitate transportation and storage.
Place the trap where crows are likely to congregate. The most attractive bait is meat or eggs. Whole-kernel corn, milo heads, watermelon, and poultry feed also may work and be preferred where carnivores, such as dogs, may be attracted to the trap. Place the bait under the ladder portion of the trap and provide water. The trap should not be visited for 24 hours after first applying the bait, but it should be checked daily when birds begin to enter the trap. Replace the bait as soon as it loses freshness. Remove all crows captured except for about 5 to be left in the trap as decoys. Remove crows that have been captured after the sun has set to facilitate handling. Release non-target birds immediately.
A well-maintained decoy trap can capture several crows each day, depending on size, location, and time of year. Cage traps, minimum size 60 x 23 x 26 inches, can be effective also. Traps should be stable and set with a light trigger.
Individual crows may be captured without injury using Nos. 0 or 1 foothold traps that have the jaws wrapped with cloth or rubber. Remove ½ of the springs to reduce the initial impact. These sets are most successful if placed at vantage points in areas habitually used by crows, or if baited with a dummy nest containing a few eggs. Check the traps at least every 4 hours. Crows that have been captured may be used as initial decoys in an Australian crow trap if allowed by the USFWS permit. The small number of captures is otherwise unlikely to affect a damage situation.
Relocation of crows is not recommended except for rescues.
Translocation of crows is not recommended.
Euthanize crows with carbon dioxide or cervical dislocation.
Check your local and state regulations regarding disposal of carcasses.
Other Control Methods
Crows can be removed with nets launched by rockets or compressed air. Crows must be prebaited to the site. It is critical for net operators to be hidden while firing the nets. Crows are wary and smart, and often difficult to trap with rocket or cannon nets.
Alpha chloralose is a stupefying agent used to capture ravens. Ravens that eat treated bait become disoriented, thereby allowing them to be captured by hand. Its use is restricted to agents of WS.