About a week ago I started seeing small seeds, resembling cherry pits, on the bottom of the birdbath in the backyard. I empty out the birdbath and fill it with fresh water almost daily and the next day the the pits, usually about 3 or 4 of them, appear in the bath.
The birdbath is under a plum tree. So, first, I thought those were plum pits, but a comparison test proved otherwise.
On the left is a plum pit, on the right a pit from the birdbath.
This test also made me realize that these pits couldn't be left behind by an animal picking at a cherry while sitting at the edge of the birdbath. Look how much stuff is still left on the pit of the plum that I ate and how clean the other pit is in comparison. Aha! So, the birdbath pits are either defecated or regurgitated after having been thoroughly cleaned by the eater's gastrointestinal tract. But fecal matter is usually not associated with these pits. Therefore, I am assuming they are regurgitated. But, by whom?
This morning I filled the birdbath at 9:55, went inside, came back out again at 10:10 to startle an American robin (Turdus migratorius) in the birdbath, which flew away. And there was one of those pits in the birdbath. Now I am suspecting that the robins are using the birdbath as their vomit receptacles.
According to this article:
[Adult American robins] were observed feeding on domestic cherries, and some were known to carry cherries as far as one-half mile to their nestlings. The ground beneath such nests was often littered with cherry pits.I still need to see or photograph one robin in the act to prove that it's them who are leaving their pits in the birdbath.
I also don't know where the closest cherry tree is. My immediate neighbors don't have one.