Any specific recommendations?

I already donated them a few thousand dollars. But how do I know if me donating a few thousand dollars makes a difference or not? I'm sure if I gave them a few hundred thousand dollars all at once I could be sure I saved some extra lives but I am not so sure for a few thousand or if it's like voting in an election.

I guess you're right and I should've been more specific. 

I want to know the most certain donation both for helping humans and the most certain donation for helping animals (mammals and or birds). 

By certain I mean most likely that it will make an impact unlike me voting in a presidential election or staying home. Whatever donation is least likely to be like voting.