I do not think that perk up your ears is used in the UK, only prick up your ears, the image being taken from the way a dog's or horse's pointed ears stand up when they hear a sudden noise. From the similarity of the two words one would think metathesis had occurred as in the Northern English brid for bird, or Chaucer's crulle for curly, but no:
Prick is a cognate of various Germanic words for stick or sting, and perk from O.N.Fr. perquer "to perch" (Fr. percher), presumably referring to the habit of birds of preening themselves when on a perch, which conveys the idea of making oneself smart or lively. The expression perk up is used in this sense, but seems to have been conflated with the idea of a bubbling percolator, of quite different origin.