Maybe you could support them with food in a kind of a shelter box, which can only be entered through a cat door...I've learned that cats are soooo smart they soon realize how to get to the food inside the box and as soon one cat will start with it the others will follow...that keeps it away from the birds...
In the beginning you can place the food so that it can be seen through the screen of the cat door and after that you can remove it to a corner away from the eyes of other hungry animals...

This works of course only when the cats are used to a covered shelter...

Whatever you try: Good luck!!!