No
It's a loving joke. They can wash if off with a little water.
Bull. The laxative will poison the bird, due to size and digestion. The birds also probably kept eating the medicine, which overdoses them.
And it doesn't matter if it was a joke or easy to wash off. The people came to enjoy their time, and they literally got stuff on multiple times. Hell, a baby got soiled. A prank should not harm anyone. And yeah, I count this as harming them.