In the final years of his life, Thoreau consolidated the detailed observations of seasonal change recorded in the later years of his Journal in a variety of lists and charts sometimes referred to as his "Kalendar." Though these unpublished materials have received relatively little scholarly attention to date, they have important implications not only for the ongoing reassessment of Thoreau's place in the history of ideas in America, but also for our changing understanding of the categories of the literary and the scientific, the human and the natural. In the Kalendar project, Thoreau enacts a model of knowing as "neighboring." Through his daily practices of walking and writing, Thoreau arrives at a new way of being-with, and thus of knowing, the non-human. Such a project poses difficulties for both literary and scientific approaches, a fact which has contributed to the Kalendar's relative obscurity. In this essay, I will map the ways that science studies, particularly the work of Bruno Latour, Donna Haraway and Karen Barad, may be useful for our understanding of Thoreau's Kalendar and for the epistemology he developed in the latter half of his career.