To better understand how past climatic change influenced mammalian communities, we used fossils from the Pit Locality of Porcupine Cave, to evaluate how two taxa responded to climatic events spanning two glacial–interglacial transitions of the middle Pleistocene in Colorado. We analyzed the isotopes of carbon, oxygen and strontium in 84 specimens of rabbits and marmots to infer (1) if feeding and habitat preferences differed across glacial–interglacial transitions, and (2) whether these taxa responded similarly and synchronously to climatic events. Our results showed no significant differences in any of the isotopic values within taxa across levels. Stable carbon isotope values revealed a C₃-dominated environment around Porcupine Cave during the middle Pleistocene, similar to what is present around the cave today. Oxygen isotopes did not change significantly across levels suggesting consistent water sources over time and preventing any correlation to the Marine Isotope Stages. Marmots did show significantly more positive oxygen isotope values than rabbits over most of the Pit levels likely indicative of hibernation. Lack of significant change in Sr isotopes indicates similarity in habitat range through time, or homogenization of landscape Sr values due to atmospheric inputs. These results suggest that middle Pleistocene climatic change had a negligible effect on the ecology of the sampled individuals around Porcupine Cave. The effects of climate on mammals are complex and these results cannot be extrapolated globally; research is needed to differentiate how global climate change affects mammals in different regions and of different life history to provide insight into how current global warming will affect extant species.