Although intra-population variation in niches is a widespread phenomenon with important implications for ecology, evolution and management of a range of animal species, the causes and consequences of this variation remain poorly understood. We used stable isotope analysis to characterise foraging niches and to investigate the causes and consequences of individual niche variation in the European badger, a mustelid mammal that lives in territorial social groups, but forages alone. We found that the degree of individual niche variation within social groups was negatively related to the availability of farmland habitats, which represent an important foraging habitat for badgers; and was positively related to territory size, supporting the idea that resource limitation and ecological opportunity lead to increased individual specialisation. We also found that the degree of individual specialisation related to an individual's body condition and that this effect varied with ecological context; such that specialisation had a stronger positive relationship with body condition in social groups with reduced availability of key farmland habitats. Body condition was also related to the utilisation of specific resources (woodland invertebrates), but again this relationship varied with the availability of farmland foraging habitats. This study supports the idea that resource availability plays an important role in determining patterns of individual niche variation, and identifies the potential adaptive consequences of specialised foraging strategies.