Who are you??

This young tabby cat has appeared in our garden this week. He jumped up on our living room window sill and looked in yesterday! He seems really fascinated by the rabbits in their run and that's where I saw him first this morning. Then he crept along the border , closely followed by our old cat Toto who must have been thinking,
"Is he coming to live here too?"
He is very similar in appearance to our Taz, so I have named him Baby Taz!