Yorkshire Terriers, or Yorkies as they are more commonly known, are a breed of small dogs that developed in Yorkshire, England many many centuries ago. They were initially used as hunting dogs to get rid of small rodents like rats and other pests. They did a good job at that! Perhaps that’s why Yorkies today are so prone to yap at things and investigate their surroundings like tiny little hunters. Because, in a way, they are.
Reference: Wikipedia article on Yorkies