Not Wild Empathy, but...

Most info is coming from the D20 SRD https://www.d20srd.org/index.htm#google_vignette

Wild empathy is a ranger class trait that uses ranger levels:

Wild Empathy (Ex) A ranger can improve the attitude of an animal. This ability functions just like a Diplomacy check to improve the attitude of a person. The ranger rolls 1d20 and adds his ranger level and his Charisma modifier

I suspect, though, that you are instead asking about using skill checks such as Diplomacy to improve the mood of animals. This is a rather gray area in the rules. The "Speak With Animals" spell says:

If an animal is friendly toward you, it may do some favor or service for you.(Emphasis mine)

This implies that skill checks on an animal you can speak with are possible, but not what the skills might be. There is a good amount of debate on other forums about Diplomacy vs Handle Animal. On one hand, the handle animal skill only talks about making an animal perform tasks and raising an animal to be loyal. On the other hand the diplomacy skill makes no mention of animals or other non-verbal creatures, and the low intelligence score of animal-type creatures...

Traits An animal possesses the following traits (unless otherwise noted in a creature’s entry).

 

Intelligence score of 1 or 2 (no creature with an Intelligence score of 3 or higher can be an animal)

May prevent them from understanding the finer points of conversation. So this is very much a DM discretion thing. Diplomacy does reference the wild empathy class trait and uses the same table, so odds are somewhat favorable for that being your answer.

Not Wild Empathy, but...

Most info is coming from the D20 SRD.

Wild empathy is a ranger class trait that uses ranger levels:

Wild Empathy (Ex) A ranger can improve the attitude of an animal. This ability functions just like a Diplomacy check to improve the attitude of a person. The ranger rolls 1d20 and adds his ranger level and his Charisma modifier

I suspect, though, that you are instead asking about using skill checks such as Diplomacy to improve the mood of animals. This is a rather gray area in the rules. The "Speak With Animals" spell says:

If an animal is friendly toward you, it may do some favor or service for you.(Emphasis mine)

This implies that skill checks on an animal you can speak with are possible, but not what the skills might be. There is a good amount of debate on other forums about Diplomacy vs Handle Animal. On one hand, the handle animal skill only talks about making an animal perform tasks and raising an animal to be loyal. On the other hand the diplomacy skill makes no mention of animals or other non-verbal creatures, and the low intelligence score of animal-type creatures...

Traits 
An animal possesses the following traits (unless otherwise noted in a creature’s entry).

Intelligence score of 1 or 2 (no creature with an Intelligence score of 3 or higher can be an animal)

May prevent them from understanding the finer points of conversation. So this is very much a DM discretion thing. Diplomacy does reference the wild empathy class trait and uses the same table, so odds are somewhat favorable for that being your answer.