It's a zoo, Iggy. Everything is behind bars.

Nudge, The Angel Experiment

In the Angel Experiment, while the Flock was in New York City, Iggy, Angel, and Max went to buy 6 small bag of honey-roasted peanuts, and Fang, Nudge, and the Gasman went to look at a clown selling balloons. Unfortunately, the clown turned out to be an Eraser! Soon, more Erasers were gathered, and the Flock ran down the city streets with the Erasers at their tail until Iggy suddenly shouted, "Left!" at a path and there it was: the Central Park Zoo. There were at least two hundred kids already going though the security gate, and Max whispered, "Merge!" and just like that, they did, surrounded by the other kids—only Fang, Iggy, Nudge, and Max had to duck to blend. Luckily also, it was a school day so no unauthorized adults could pass unless they had a chaperone pass; the cops at the gate blocked the Erasers from entering, and the Flock escaped from danger once more. But once inside, the Flock couldn't stay there for long without feeling sorry and sick for the caged animals, remembering that this was the way they used to be, too. Soon, sure that the Erasers were gone for good for the time being, they hightailed it out of there.