What is on my RBTA?

[Chortanator]

Just came home from work and saw this on my RBTA. Was not there this morning

 

[Chortanator]

Update: I looked back at it and it seems to have gone away? No trace of it anywhere

 

[T_BONE]

Mine gets that from time to time. No idea why but it happens quite often. Not a pest as best I know.

 

[Treasure Coast]

Might be partially digested food it spit out or it went to the bathroom?