Due to his advanced age, Jonathan spends his days doing almost everything with his mate, including eating, sleeping and mating.[13] The sex of Frederica, one of two of his favourite tortoises thought to be female (the other being Emily), as well as his companion since 1991, was cast into doubt in 2017 when island veterinarian Catherine Man indicated that due to a deformity of its plastron its sex could not be verified,[4] and is now known to be male, being renamed Frederik.[1] While Frederik was undergoing the examination, Jonathan came over and did not leave the side of Frederik and the veterinarian during the entire process.