The diet of livestock foraging on rangelands is highly diversified and changes daily, seasonally and annually. Thus, a classical assessment of diet nutritive value with forage sampling followed by chemical analysis would be too challenging. We explore an alternative method to characterize the diversity of food offered based upon the classification of food items into a limited number of “ functional” nutritive classes. The area of study was a Mediterranean garrigue rangeland, grazed by sheep in spring. Based on sheep foraging behavior, 103 food items were identified as “ bite categories” (BCs), from 60 plant ant species; 245 samples were taken. They were oven dried and grinded before Near-infrared spectra (NIRS) collection. Hierarchical classification of NIRS spectra produced “functional” classes of BCs. A few classes were homogeneous while others gathered plants from diverse botanical origins, but displaying similar characteristics such as chemical composition. Other Mediterranean rangelands and other grazing periods need to be studied in order to validate the functional nutritive classes identified. This method paves the way to better characterize the potential nutritive value of rangelands by taking into account foraging selection at bite level.