Inscriptions dating to 1543 on Portuguese Rock attest to the presence of shipwrecked Portuguese mariners in that year, and other Spanish and Portuguese visitors introduced feral pigs throughout the 16th century with the intention of providing food for future visitors or settlers. Many of these crews called at Bermuda in search of fresh water and meat, but no attempts at permanent settlement were undertaken. In fact, the eerie sound of cahow birds (see above) calling at night led the Spanish and Portuguese to believe the islands were haunted; they were sometimes referred to as the Isle of Devils. This is an interesting parallel with Norse mythology, the underground noises of other species of nesting petrel and shearwaters being thought to be the origin of trolls.