Damages of carrion crows in farmland

Carrion crows are known to cause damages in crops, particularly in maize fields. What can be done to prevent such damages?

Aims

The Swiss Ornithological Institute compiles and evaluates procedures and measures against carrion crow damages in collaboration with farmers, agricultural institutions, bird conservation and animal protection agencies.

Approach

In March 2003, we experimentally tested the effectiveness of gas balloons for deterring carrion crows in a waste dump in the canton of Ticino, Switzerland. We noted numbers and locations of carrion crows on an area of 60 x 90 m in relation to a) no balloons in the air and b) the presence of three balloons during four days. The test balloons were helium-filled red latex balloons 75 cm in diameter attached to ropes 20 m in length.

In fall 2003, we additionally conducted inquiries by telephone of more than 30 farmers about their experiences with using gas balloons to deter carrion crows.

Significance

Each spring, the Swiss Ornithological Institute is contacted by anxious or aggrieved farmers asking for help in relation to carrion crow damages and the possibility of defence strategies. Our project allowed to evaluate the effectiveness of one of the most promising measures of crow deterrence and, based on the results, to give well-founded recommendations. The project is thus primarily of applied value.

Results

Both the experiments and the telephone inquiry suggest that gas balloons are suited to scare crows from crops, at least for a limited period of 3-4 days. To achieve long-term protection, however, various deterrence measures have to be applied alternately and in combination. The most promising measures appear to be those related to how crops are grown and to when measures are implemented (ideally during the most vulnerable stage of the crops).

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Damages of carrion crows in farmland

Aims

Approach

Significance

Results

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