Minecraft wiki entry for Chicken_Jockey, associated text: Chicken jockeys generally run around, behaving like the zombie, instead of using the chicken AI. ‌[Java Edition only]
Chicken jockeys fall slowly and do not take fall damage, like normal chickens.
The chicken moves at the speed of the baby zombie, which is much faster than a normal chicken.
Command spawned jockeys are an exception.
The chicken can run through 1 block high gaps. The baby zombie suffocates unless the above block is transparent.
Chicken jockeys can pick up/equip items.
The chicken (unless spawned with commands without the IsChickenJockey tag) does not lay eggs. However, they can still be bred into regular chickens.
The baby zombie and the chicken can be separated by using a bucket of water on them.
In Creative mode, a chicken jockey that isn't already targeting a player follows a player holding seeds, like a normal chicken, and can be fed. In Survival mode, unless the zombie is a zombified piglin in a non-aggressive state, the chicken jockey targets a player who attempts to do this, and the chicken cannot be fed.
Chickens become passive again if the rider is killed.
Zombified piglin chicken jockeys are the only jockeys that aren't hostile.