Interesting topic..
...my heartache to no end whenever one of my chickens passed away, but I do not feel that its souls linger on, once it gone, it really is gone. I did read somewhere it says chicken does not have an individual soul, but a collective soul.
I believe dog has an individual soul. My mom was in the hospital for 3 weeks. I looked after her companion dog, this dog Blossom was with mom for almost 20 years side by side and had a human a bed next to mom's bed.
One night mom saw Blossom was at the hospital looking at her, the next morning Blossom dog died, I was with her at her last minute. I rang mom so mom can say something to her Blossom. Blossom was shaking her body, but her eyes lighted up upon hearing mom's voice and she took its last breath. Mom saw her Blossom here and there in her home, she thinks Blossom still visit her, but then...it might just be she used to see Blossom by her side for so long.