I was playing around in creative mode when i had no internet. I placed a dispenser facing right at the nether portal and I connected a 1-tick clock (blinking mechanism) to the dispenser. Then i filled the dispenser full of Zombie spawn eggs.
My plan was to have all those zombies go into the portal and have them all squished in one block in the nether. I also had a lava fountain over the portal. After the spawn eggs was out, I went in the portal, and all those zombies exploded into lava!
On one attempt i left the dispenser to spawn and I did something else. When i came back, i found this Chicken Jockey. I never seen one before. I looked it up and this was actually implemented in 1.7, but they did not mention it in the release logs.
Yep. There real. I saw 2. I only do creative mode in SP (you all know why- especially the creepers) so I used a crap-ton of zombies I spawned and did a few tests. I spawned some more in and behold! A chicken jockey. And another.
You can also have baby villagers riding chickens. I also discovered that baby Zombie Pigmen can ride chickens when a few chickens wandered through my Nether Portal. shows how to improve your chances of getting one.