So, in the case of literal scarecrows, any bird that is naturally less frightened by the scarecrow will be at a disadvantage because they will also be slower to

So, in the case of literal scarecrows, any bird that is naturally less frightened by the scarecrow will be at a disadvantage because they will also be slower to get spooked by the actual farmer (this only worked when scarecrows were dressed in similar clothes to actual farmers, who would periodically come out with a rifle and kill a few birds). In the case of the laser, I don't see the downside for the birds that decide to ignore the laser, and they get extra food, hence more offspring next year. I would not be surprised if this stopped working in 5 years or so.