I ran a big hatchery that was covered in standard chicken wire that was about 20 years old. The bastards figured out that they could walk on top of the ceiling, and they worked the wire with their feet enough to create holes, some big enough to get their bodies through. I'd come in in the morning and there'd be a dozen squawks and blues in the cage. Took me a while to figure that one out.
The owner used to have a fishing club on the creek by the hatchery. That worked until the pelicans found it. Wiped it out in less than two weeks. Some birds ate some much trout they couldn't fly.
Once herons find a guaranteed meal, they and their five dozen descendants will return until it's fished out. Best to nip it in the bud.
