I agreed to foster a pregnant mom last August. One week later she gave birth to 7 kittens--2 males and 5 females. I intend to keep the mom and 2 of her kittens. I have already adopted out 3 others. That leaves 2 to find forever homes. Anyway, yesterday morning I had the mom and the 4 kittens 'fixed'. They are home now and sleeping, sleeping, sleeping. When they are awake they hiss and growl when another gets near them. Does anyone know what causes this agressive (defensive?) behavior and how long I can expect it to last? Thanks for any information/advice you have.