The Root of the Behavior
Dogs in the wild would have had no choice but to try to find a secure location in which to deliver their puppies and to keep them safe from harm while they raised them to become independent members of the pack. Since puppies are completely dependent upon their mothers in the early weeks of life, the pregnant dog needed to find a spot with adequate warmth and shelter but one that would also be hidden from plain view. In the wild, death by predator attack would be a very real possibility for dogs who had just whelped a litter. The necessity of finding secure accommodations for both whelping and caring for her puppies would be paramount. Camouflage is a critical element of the nest in the wild. Because mother dogs require nutrition in order to produce quality milk for her babies, it would be necessary for the mother dog to leave her young for short periods of time to hunt. Without her there to protect her puppies, the ability to conceal them from predators would be critical. This camouflage is found in the choice of location but can also be aided by outdoor elements like branches, grass, sticks, and brush. All of these items could provide necessary coverings to disguise the puppies from nosy animals seeking their next meal.
Encouraging the Behavior
By nature, dogs are animals that like to live in dens. Nesting is an important part of getting the 'den' ready for the arrival of puppies. This is why it is vital that you introduce your dog to the area you have selected for her to whelp her puppies in well in advance of their arrival. You want her to understand that that space is hers alone. Many owners choose a specific small room in their house in which to set up a pen. These rooms include sleeping areas for the dog's owner as well. In anticipation of the big day, some owners opt to sleep in the whelping room-and some right in the box with their dog!-to help the dog feel comfortable and to 'claim' the space as her own.
Other Solutions and Considerations
Interestingly enough, these behaviors are also seen in spayed dogs though to a different degree. If you have ever observed your girl digging at blankets or repeatedly circling before finally sinking down to rest, you have seen nesting at work in your dog. Burrowing is a natural instinct in our dogs. For dogs in the wild, it played a role in helping them to create a space that would provide warmth in the outdoors. Circling allowed the wild dog to tamp down the earth in the hopes of making a more comfortable bed. It also provided the benefit of chasing off any animals that might be lurking in the soil such as snakes. Today, our dogs have no fear of these things, but the instinct remains intact and every once in awhile we are privileged to catch a glimpse of it.