Whats the last column of drawings for?
I put the poulty farm in its own room filled with nest boxes. When I want more birds I just lock the door and leave it locked for a while, maybe a year. Then I get more birds.
Unlock the door and dorfs will harvest eggs.
I only need to lock it up every once in a while when the population is getting low.
I use what Hyndis does and how your method more effective?
The last column shows how birds get in to lay the eggs. I don't
think fliers trip pressure plates, but even if they do, they can fly over the hole. (oh and the whole weight setting thing i guess)
My method results in eggs
and hatchlings every season; put some nest boxen behind the door and some in front of it. It also doesn't lock the birds behind a forbidden door, so you can butcher them at will. My door is mainly so you can expand without disassembling the whole thing every time, but it can also be used to stop a birdsplosion if your butchers are falling behind.
Couldn't you just forbid traffic, or does it not work that way?
Nope. Traffic zones don't determine where dwarves go, only how they get there.
Is there something I'm missing? My bird pen is outdoors with a few nest boxes. Every pet bird of a migrant gets sent there. My stocks screen says I have 210 eggs. I figured they were just being collected and put into the food stockpile. Am I going to lose them?
Eggs only hatch if they're left in the nest box. If you want more birds, you have to prevent the dwarves from collecting the eggs somehow. And birds have fairly low lifespans, so you'll need more of them eventually.