In the summer and spring, he will sit for hours and chirp at the birds and squirrels and his whole body would quivver when he does it. I could pick him up and walk to the door and whisper "Are there any birds and squirrels out there?" and he would do it. One day, I swear him and a squirrle carried on a conversation. One would chirp, the other would chirp back and that went of for a good 15 minutes. He was the first cat I saw do that.