Urban expansion and associated habitat fragmentation are expected to be detrimental to global biodiversity. Natural habitat that is extensively modified often poses challenges to native fauna that must adapt to new conditions to survive. While some species decline in numbers or become locally extinct, the Eurasian red squirrel (Sciurus vulgaris) successfully inhabits cities. Because squirrels are sensitive to habitat fragmentation and their space-use patterns are influenced by the distribution and abundance of major food resources, their movement patterns are likely to be modified in response to changes in environmental conditions brought about by urbanization. Therefore, to investigate whether supplementary food resources are key to its success, the home ranges of squirrels inhabiting a large city park were related to both natural food sources (NFS) and anthropogenically-provided food sources (PFS) in 3 seasons. The combination of home ranges that were relatively small, year-round food availability and the lack of a seasonal body mass change indicates that the semi-urban environment can be high-quality habitat. The squirrels’ home ranges encompassed areas with a year-round NFS supply, but they shifted their home range core areas closer to PFS in seasons where they were more reliable, even though NFS were also abundant at the time. Additionally, heavier individuals’ core areas were located closer to PFS. Consequently, our results show that human activity (i.e., via PFS) had a direct, measureable effect on squirrels’ feeding habits and movement patterns even though NFS were available. However, the consequences of urbanization are not always detrimental for native animal species and an improved knowledge of energy resources and their effect on habitat use is important for understanding and minimizing the long-term impacts of humans on urban wildlife.