neighbourhood cats

Question
i have 2 cats one 4 yr old male and one 18 month old female, both have been fixed but for the past few days there have been  3 other cats hanging around our haouse day and night meowing at our windows through the night. Why would they be doing this when our female cat is fixed.
she sits on the car and they just sit on the floor starring at her, they even come into our backyard where we have a dog that isnt too keen on other cats, he has chased them away a few times.

Answer
Sheena,

If the surgeon simply tied or obstructed the Fallopian tubes in order to make the female cat sterile, she would still come into heat, attract males, and attempt to breed.  Experience has shown that the best procedure is to perform a complete ovariohysterectomy.

You may want to take her to the vet to see if possibly a part of the cat's female parts were left in. If so, they can redo the spay to it is a complete one.

Tabbi