In the winter, rodents seek out warm places with food to make it during the cold months. Your house has both of these things. It is like an all you can eat place for them.
Most homes have some sort of mice in them, at least in the walls. They will squeeze in a crevice or in a crawl space. Mice can fit into a whole the height of an eraser. Rats can fit into spaces as big as your thumb. Rats are strong swimmers and can swim in sewers and climb up into homes from sewer pipes in rare instances.
Most people are not worried about mice or rats unless they see them in there home, then they are priority one. Aside from seeing them, you can look for signs of activity. Look for droppings, bite marks, rub marks on doors or wood furniture. Your pantry will have damage to packaged food.
Rodents often make nest from paper or other soft material to keep them warm. Look for chewed or shredded products as a sign of rodent activity.
Rodents have diseases that are transmittable to humans. This is the most important reason for rodent control in your home or office.