In theory it works, I've seen it work. But in practice I'm afraid a theme park will be so full of edible trash that the crows might question the reasoning behind picking non-edible trash up to get a reward.
Give the Brawndo, it's what plants crave. Seriously give them what they like to eat. Make it addictive like we do for fast food. Not only will you have birds that do your bidding, but they'll be nice and fat so you can catch 'em if you need to later.
