As I understand what's going on here is, sentient is being used to state the ability to reason with your surrounding in an intelligent way; primarily through complex communication. While animals may be conscious of their environment and can discern certain things like danger and who belongs to their pack or clan, I'm not convinced animals actually FEEL love or compassion or the ability to reason. So, we apply those human emotions to what we see them doing; mostly, I think, because it humanizes animals.
See.. this is the meaty meat meat I was waiting for... dolphins, elephants and great apes certainly do.
There are many studies that have been able to discern actual abstract thinking, tool use, culture, fission-fusion social structure including tracking alliances and other cooperative behavior, acoustic vocalizations, foraging methods, etc.
remember Koko the sign language commuicating gorilla?
http://articles.latimes.com/1985-01-10/news/mn-9038_1_pet-kitten
Koko, whose favorite picture book stories include "The Three Little Kittens" and "Puss 'n' Boots," asked for a kitten for a Christmas present a year ago, researchers said.
"But we gave her a life-like stuffed animal and she was terribly upset," said Ron Cohn, a biologist with the foundation. Koko refused to play with it and kept signing "sad."
So on Koko's birthday last July, she was allowed to choose a kitten from among several in a litter. She named the gray-and-white kitten "All Ball" as a joke, Cohn said. "The cat was a Manx and looked like a ball. Koko likes to rhyme words in sign language."
***flash forward (there is more into in the article for those who care to read it)
In mid-December, All Ball wandered onto the highway near the seven-acre research facility and was run over.
"When we told Koko, she acted like she didn't hear us for about 10 minutes," Cohn said. "Then she started whimpering--a distinct hooting sound that gorillas make when they are sad. We all started crying together."
Koko then said, "Sleep. Cat." by folding her hands and placing them at the side of her head, Cohn said.