@Tamrakshar, Great suggestions from everyone. You are against killing the bird and your wife wants to kill the bird as the bird is destroying the plants she is growing with love. There is a solution that can be used without hurting the bird. Have you tried Stop Bird Pro, a device that emits modulated high frequencies. It acts on the nervous system of the birds to repel them from reaching out to the territory which you would like defend. I understand it works to the range of 500 sq.ft. and I am sure it would work well to prevent the birds reaching out to your windowsill. I am rushing this suggestion to reach out to you within 30 days given to you to solve this problem.