William's Picks
Erin Hunter wrote the Survivors series about dogs, the Warrior series about cats and the Seeker series about bears. My favourite was the Survivors series.

Survivors series by Erin Hunter
This is my favourite series by Erin Hunter and I highly recommend it.

The series is about dogs who have to survive in the wild. 

There are four books. 
In the first book the main character, a golden retriever named Lucky finds a pack. 
In the second book, he encounters a competing pack.
In book three, the main character joins the two packs. This is my favourite book.
In book four, acid rain harms the pack's habitat.

I recommend you read these books in order.
Warriors series by Erin Hunter
I liked this series as well: this is my second favourite series by Erin Hunter. There are six books in the first series of this.

The cats are in clans and fight each other for territory in the wild.

My favourite was book six: the Darkest Hour where all the cat clans have one common enemy.

I did not read the other Warrior series because I found the books were starting to be very similar.
Seekers series by Erin Hunter
This series is about three bears surviving in the wild.  This is my 3rd favourite series by Erin Hunter and I also recommend this series.

You will like this if you like the survivors series or the warrior series.

My favourite book was the first. This is the book where the bears find each other.