meat bird tractor question - how do you catch the birds?!

Sorry, I'm sure the answer is right under my nose, but how do you catch the birds in those low profile tractors when it is time to slaughter? I've been studying meat bird tractors for a few days and can't figure how you get them all to come out of one opening and not run to the other end? Thanks

 

I was wondering about that. I guess I gave them more credit than they are due. I figured the first few would be fooled by the food, but after a few were caught and crated, they would begin to wise up.