The funny part was the crow egging them on. I adamantly disagree with those who say the crow was trying to break up the fight. That is totally foreign to a crow's nature and instigating trouble and playing pranks is absolutely their nature.
To me that is one of the fascinating things about crows and ravens. They are so smart that they have the time to spend playing games whereas most animals can't spare a moment from their search for food, shelter and evasion of predators.
I am not sure whether Ravens In Winter would hold the interest of a 9 yr old. It could be a little dry for a child that young. (it has been quite a few years since I read it so...) If your 15 yr old likes animals, birds and stories about them he or she will probably like it. It is written from the author's perspective of being somewhat of an amateur sleuth who sets about making his own research experiments. What he finds is amazing and the things he gets himself into are amusing.
Oh yea, those two cats were fighting street cats. Probably feral like you said. Now that you’ve described the book, it sounds like my 9 year old might like it. He’s very into nature and adventure. I’ll have to check it out. Thanks.