I find this very confusing.
Berries - blackberries, raspberries, strawberries etc. do not have a pit. The fruits that have pits are things like apricots and peaches.
As a human who grows and consumes many varieties of both I am pretty confident that I would have trouble swallowing let alone digesting a pit (aka stone) from one of those fruits.
I think the controversy comes primarily from apple seeds because they are much smaller and therefore easier to swallow and digest. They contain a compound called amygdalin which converts into hydrogen cyanide in the body. Hydrogen cyanide is toxic.
I have used apple seeds to add a bit more real almond flavor in baking (commercial almonds have been bred to not have the bitterness which is a shame as it really enhances the almond flavor). I once calculated how many apple seeds I would have to eat to approach toxic levels of cyanide and I forget now but it is a vast amount!
Similarly birds would have to eat a lot of apple seeds to have any ill effects.
I routinely toss an apple core or two to my chickens. I don't know if they eat the seeds or ignore them.
This may be helpful.
https://queenslanderaviaries.com/blogs/news/can-apple-seeds-kill-my-bird