Giant pandas (Ailuropoda melanoleuca) are specialized bamboo (Bambusoideae) eaters with a simple, carnivorous digestive system. They are known to employ diet switching (i.e., selecting different parts and species of bamboo depending on season and reproductive status). Our objective was to explore whether seasonality or changes in reproductive hormone concentrations had a significant effect on diet switching in captive giant pandas. We determined the mass and nutrient intake of each plant part ingested by one male and one female panda held at River Safari (Singapore). We classified the plant parts as young and old selections of leaves and shoots. Each panda was offered a combination of 3 species of locally raised bamboo. We analyzed the reproductive metabolites of our female panda to determine whether an interaction of estrus and season may affect seasonal diet switching. Ingestion of young leaves, mature leaves, and stems were significantly affected by season. Stalks, however, were ingested year-round in similar proportions. When grouped together, leaves and stems were also ingested according to season. We did not detect any effect of hormones on the nutrient intake of the one female panda. Selection was entirely based on plant parts, and not nutrient content. Therefore, diet switching may not be a good behavioral tool to use in assessing onset of the mating season. However, the large amount of concentrated feeds in our panda's diet may have prevented any significant nutrient changes throughout the year.