Indigenous food sovereignty relies on ecological knowledge of plants and animals, including knowledge related to their development and behavior through the seasons. In the context of anthropogenic climate change, ecological calendars based on Indigenous knowledge may enable communities to anticipate seasonal phenomena. We conducted research with communities in the Standing Rock Nation (North and South Dakota, USA) to develop ecological calendars based on their ecological knowledge. We present ecological calendars developed in seven communities through a series of workshops and interviews. These calendars are rich with knowledge about temporal relations within each community's ecosystem, including the use of plants and animals as seasonal indicators and cues for food system activities. However, the calendars also reveal the impacts of cultural genocide wrought by the United States government in its efforts to colonize the lands and minds of Indigenous communities. Given the diversity of knowledge among Standing Rock communities, we identify opportunities for knowledge exchange to revitalize ecological relations at the heart of food sovereignty. We highlight the potential for ecological calendars to facilitate climate adaptation by enabling communities to synchronize their food systems with an increasingly variable climate.