To aid in the development of a long-range subcutaneous radio frequency identification tag to monitor the fate of sea lion pups, the dielectric properties of the cranial skin of young female otariids, and possible test subjects of similar size and age, or pigs (Sus scrofa) and sheep (Ovis aries) were obtained over a frequency range of 0.1-10 GHz at the base of their heads where the tag will be implanted. The resulting curves were similar in shape to adult human skin data, but the values were generally lower. Between subjects, variations were noted in all the species. Circuitry for the RF-ID tag is being designed to account for antenna detuning as a result of the lossy media or skin and the variation in dielectric properties.