You're waaayyyy more tolerant than me.
In your shoes, I would have just trapped all the hens wandering over and I would take them directly to my local Animal Control (who does handle livestock). While there, I would mention how absolutely starved they were and how they were stealing from my feeders. I'd also point out that when I picked them up, they felt emaciated. This ensures they feed them properly for recovery while they hold them for an owner to claim and if the owners did, they'd be properly educated and possibly a wellness check on any animals back home as part of having birds returned.
If they even thought to check with animal control. They read as very uncaring, like people who would just assume a predator got them and shrug it off, meanwhile the birds would get adopted out in a much healthier condition than when they arrived.
Edited to add: Yes I've done this before, multiple times, no I don't regret it. People like that get mad at the animal control who has their animal(s) and don't even think about who might've brought them in. Assuming they cared enough to even notice (most don't notice or care).