Chicken movement bias

After using an array of dispensers attached to a fast clock to hatch multiple chicken eggs (not spawn eggs), I noticed that the chickens were all crowded into one corner of the cage. I found that all the chickens were attempting to move north east for some reason, and thus bunching together in that corner.
In the first picture I show the empty space highlighted in green, and the dense inhabited space highlighted with red. In the second, I show several chickens who were pushed through the walls of the cage, yet still showed continued northeasterly movement patterns.