The cold weather we recently experienced has forced rats to search a wider area for food. and new, warmer locations to live. I even had an issue with them trying to relocate to one of my sheds (not a wise move.) Obviously during extreme spells of weather these rodents have to try and exploit every food opportunity that presents itself to them. People keen to ensure the birds in their garden are able to make it through the harsh conditions tend to to over feed the birds, this offers a feast rats can hardly be expected to over look. Now we are through the worst of it I would advise that when you have the time you check all sheds, outbuildings, compost areas/bins and pet/ livestock housing and food storage areas to make sure you do not have any unwanted guests. If you find that you do and the problem is not one you feel comfortable dealing with, just pick up the phone.