This article examines the various linguistic registers in the corpus of writingsproduced by the Jesuit missionaries in Canada in the seventeenth and eighteenthcenturies. These manuscripts, which focus narrowly on the daily activity of themission, were written in several Amerindian languages and in Latin. They make itpossible to underscore the quality of the missionaries’ attachment to the cultureand environment of the Amerindians. The manuscripts have, however, often beenneglected by a historiography dominated by reference to the Jesuits’ Relations. An analysis of ornithologicalvocabulary allows us to explore the Jesuits’ perception of nature in Canada, whilerevealing how the very conception of the mission mutated during the seventeenth andeighteenth centuries.