Minecraft wiki entry for Chicken_Jockey, associated text: The baby zombie's hitbox is larger than the chicken's. Attacking the chicken may harm the zombie instead, unless the player carefully attacks its feet.
Chicken jockeys, like spider jockeys, cannot pass through portals.
Zombified piglin chicken jockeys can spawn from portals in the Overworld.
A normal chicken jockey may spawn in the Nether if a zombified piglin calls a normal zombie as reinforcement.
Name tags prevent the chickens from despawning, and they can be bred to spawn normal egg-laying, non-despawning chickens.
The wither attempts to attack the chicken being ridden by the zombie and the zombie also takes damage.
Adult zombies and zombified piglins can also control a chicken while riding on it, though they do not naturally spawn on chickens.
A zombified piglin chicken jockey does not become hostile if the chicken is killed or attacked.
Chicken jockeys spawned using /summon use the chicken's speed instead of the baby rider's speed.
To prevent a chicken jockey from despawning, only the chicken needs to be name tagged, because riders of other entities never despawn.
In Java Editon, if a zombie villager chicken jockey is cured, then the villager continues riding the chicken even after it grows up.[2]