Death and Chickens

Grim isn't killing the chickens. They just don't have that long of a lifespan. Unless you turn off animals aging in your game, you'll likely see Grim a lot.  Also, one thing that might help is to stagger the purchase of new chickens so you're not losing all of them at once. I know this can be disturbing. Every time I pop into the lot where my Cantrell kids' parents live, it does seem Grim is there. Joseph has a farmhand, too. Best of luck. If you need to know where to turn aging off for the animals, go into Game Options. Click on those little Ellipses dots (three dots in the upper right) Click Gameplay and from there you will find the option once you scroll down the page.

Yeah, Grim does take them, but only when their number is up. I bought two chicks, one grew into a hen, then 2 or 3 days later, the other one finally did, too. So, you can stagger buying them, but that's also not a guarantee.

He'll come and collect your horses, llama, cows, wife, husband, children, parents and more, when their number is up; their time on this Earth has elapsed; it is time to shed their mortal coil.

Death is actually neutral. It's job is to take beings with no preferential treatment. So, he's just doing his job. 

Also, feed them vitality treat, I believe it's called. That prolongs their lives. 😉