How daft am I?? Took me ages to see the one behind!! D'oh
What a strange place for that cat to sit!
the cat on my windowsill has been with me for years and has only ever moved off of that place occasionally for me to give him a quick going over with the hoover (he's not real).
when i first got him i used to keep him on the parcel shelf of my car until one day going back to my car from shopping there was a crowd of people round the car and they were going to call the police and report me for animal cruelty, he has been on my windowsill ever since.
I think something must be nesting in the eaves of the house next to you and that is what the cat is so interested in.
Lynne x