I can't explain the increase, but one factor may be significant.

My decoy bird came from a friend who lives 80 miles away, whereas in previous years I've employed locally caught birds.

Do you think this strange bird on the patch could have made any difference?

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Our carrion crow population is divided into territory-holding pairs and non-breeders.

Territorial birds are dominant, with the males in turn dominant over the females.

Studies have shown the boundaries of a pair?s territory are most vigorously defended against unknown intruders, while familiar individuals from the adjoining territory are more likely to be tolerated.

This has the advantage of mutual defence against non-territory holders on the borders.

Thus it follows that a decoy bird brought in from some distance away is more likely to excite the residents than a local bird.

It would be interesting to hear from other readers whether they have noticed anything similar.

Given a choice of decoy bird I would always opt for the bird caught as far away as possible from the area in which I was trapping.