Exclusion
Exclusion generally is not practical for most crow (Corvus sp.) problems, but might be useful in some situations. For example, nylon or plastic netting might be useful in excluding crows from high-value crops or small areas. Protect ripening corn in small gardens from crow or other bird damage 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 by the corn tassels, a necessary step in corn grain development.
Lines
Another excluding or repelling technique used historically to protect fields from crows is stretching cord or fine wire at intervals across the field at heights about 6 to 8 feet (1.8 to 2.4 m) above the ground. Sometimes aluminum or cloth strips or aluminum pie pans were tied to the wires. More recently, the concept of stretching widely spaced lines or wires over or around sites needing protection from certain birds has received increased attention. Crows were included in two studies at sanitary landfills, but results were somewhat conflicting. One report from South Carolina indicated that a 20 x 20 foot (6 x 6 m) wire grid repelled crows, but another from New York indicated that parallel wires stretched 10 x 10 feet (3 x 3 m) apart and 80 x 80 feet (24 x 24 m) above the ground did not repel them.
The reason this technique has worked for certain birds is not completely clear, but the wires appear to represent an obstacle that is difficult for a flying bird to see, especially when rapid escape may be necessary. Various species respond differently to lines, and generally adult birds are more repelled by lines than juveniles.
Other factors such as season and/or biological activity of the birds, type of lines or wires, spacing, and height need further research and development to better understand the potential usefulness of lines in bird management.
Resources: (online)
Crows
