Help needed, dead chick

[Eggcessive]

If there is some difference in age, they could be pecking each other. At 5 weeks they are establishing a pecking order, and if they are bored or overcrowded, there could be some aggression. But I would look for symptoms of coccidiosis, and treat if that may be the reason for the blood on vents. Here is some reading about coccidiosis:
https://thepoultrysite.com/publications/diseases-of-poultry/206/coccidiosis

https://the-chicken-chick.com/coccidiosis-what-backyard-chicken/

 

[Kiki]

I'll grab some stuff for cocciodosis and treat them for that. I didn't see any abnormal poops in the run but it's a decent size so there may be some that I can't see. They aren't in with older chickens, they're in my nursery run with chicks just they're own age. I'm not there at the moment so can't double check the run for poop just yet.

Great, see if you can get it today.
Coccidiosis can kill fast.