I observed flock of Oriental Greenfinch today. The number of individual approximately 20. And in that flock, One individual did "Cleaning bill" continuously. Other individual did feather grooming but this male Oriental Greenfinch did such so iIt stood out. Maybe he foraged some seeds that not be eaten by Oriental Greenfinch usually and he foraged the seed with mistakes.
Cleaning own bill is very common behavior and we can observe it easily. Carnivore and Omnivorous species do that frequently, and many frugivore also do that frequently. Granivore alparticularly "Ovule" forager do that. And avifauna don't prefer sticky. So if something sticky materials adhere to bill, they do bill cleaning. In some case the bill cleaning is used for play. In my home, a Large-Billed Crow put out the sound "dyurururu-" with its bill and the roof of warehouse. It was morning so I was awakened from the sounds and I think it was funny event for me.