lease violation allowed by apt. manager?

nope contact your local housing authority

No one can violate the terms of the lease. If the landlord allows some people to do this, then they are playing favorites and allowing these people to take advantage of the system. If this is the manager doing this, speak to the owner (if you're in a big complex, which it sounds like it does) or another manager. If it's the owner, talk with one of your managers. Check out the property's website and find someone who's above them to speak with.

You can ask the land lord to speak to the tennants however its not illegal to put out bird feeders. The problem DOES NOT fall under the tenancy act & evicting a tenat because they put out bird feededs that anoy the neighbours is not a strong argument.

IT DOES HOWEVER fall under your local city council. (the part of the local law that fall under neighbour laws like leaving rubish on your front lawn, attracting rates ect...

So you will have to complain to your local concil...They do try & ask if you have at least attemptented to resolve the problem your sel..the best way being an anonymous letter to the neighbours ( not the land lord he cant do anything) first so you can say you have tried.

Just how much of a disturbance can those pesky birds actually be making?

the rules are for everyone, aren't they? I guess you have to find out who the owner is, and let them know that management is playing favourites?