https://www.chickenfans.com/do-chickens-mourn/

When two chickens are close, they'll mourn each other's death.

https://backyardfarmlife.com/is-your-chicken-sad/

When it comes to the capability of chickens’ emotions, it’s known that chickens experience friendship within the flock, experience grief at the loss of a fellow chicken, and chickens can even miss their owners.

https://bestfarmanimals.com/why-is-my-chicken-dying-everything-you-need-to-know/

There are instances when chickens bond closely and grieve when one of them dies.

https://backyardhomesteadhq.com/chicken-feelings-do-they-miss-each-other/

Chickens are thought not to understand the permanence of death, and so not to be able to grieve . However, they do display some empathetic awareness of when another chicken is sick or dying.

You wouldn't believe how quickly I found all that! The other thing is: if you applied that logic to people, it becomes problematic very quickly, and there's nothing about animals that precludes them from deserving the same hesitancy around those problems.