Like I said earlier my cats are strictly indoor (all fours are declawed), and we live in a townhouse too, but one nice day I thought I would put a leash on Dawn and let her roam around the yard...with me holding the leash...not a good idea.
For the next few days she tried to dart out the door...it took the squirt bottle and FIRM no's to get her to stop.
To this day I am not sure if she really got it out of her system....she will run down to the garage area whenever she hears that door open....and she has escaped into there. I am scared one day she will escape right out that door.
Although they are indoor cats she has to wear a collar with a bell to warn us she is around or coming to avoid quick escapes.

What I learned is the leash will prolong the meowing episodes and sends mixed messages...

If you don't mind the cats going out, but the area isn't safe from them to roam maybe try a cage. I saw a HUGE kitty cage at Petco the other day. I mean HUGE (was designed for cats but a German Shepard could fit comfortably)...maybe that would be something to consider...they can watch the birds, but be safe "inside"