Technically, Rhinos do not offically have Thumbs; We have hooves. But the idea translates fairly easily, unless We feel persnickety. And Rhinos do not get persnickety on any regular basis.
Having a Green Thumb means possessing skills with growing plants, and Rhinos certainly shine in that activity. We are not Planters, but We sure are Major Fertilizers, in a whole bunch of ways. Additionally, We leave the seeds of the plants We eat all over the place. (The plants plant themselves, as a general rule.) These endeavors are just one more Rhino Assignment, which We gladly shoulder as Global Participants.