French buccaneers were established on northern Hispaniola as early as 1625, but lived at first mostly as hunters rather than robbers; their transition to full-time piracy was gradual and motivated in part by Spanish efforts to wipe out both the buccaneers and the prey animals on which they depended. The buccaneers' migration from Hispaniola's mainland to the more defensible offshore island of Tortuga limited their resources and accelerated their piratical raids. According to Alexandre Exquemelin, a buccaneer and historian who remains a major source on this period, the Tortuga buccaneer Pierre Le Grand pioneered the settlers' attacks on galleons making the return voyage to Spain.