The best defence is prevention dustypuss
And it seems you are doing that. For the time being keep a sharp lookout all around the house for any place a squirrel or bird 'might' be able to 'squeeze' into; and you would be surprised just how small an opening they require.
Once they make a nest they will always come back, from-time-to-time, to see if it is available. I had a family of Starlings and so did the house next door. It took me several months but eventually I blocked off all access points; early Spring is the crucial period for looking and sealing access points. But it was worth it.
The people next door let it go on for two or three years and now the birds and a squirrel come back and try to get in through the roof tiles.
Good luck.....if all else fails, call a pest control company or your local Council Services (both charge a fair amount), who will probably use poison bait -- even on the farm I hated that action, but rats are a whole different kettle-of-fish.
Old Salt