The benefits of nature-based tourism to biodiversity conservation are often presumed but rarely quantified. The relative value placed on attributes of nature parks is unknown, as is the contribution of biodiversity to tourists' willingness to visit a particular protected area. We surveyed tourists and foreign residents in Uganda to determine how preferences for particular protected areas are formed. We evaluated tourists' demand for elevated biodiversity levels (increased numbers of bird species seen), relative to other protected areas attributes. As the number of bird species increased, tourists demonstrated increased willingness to visit a protected area, independently of all other factors. We used these results to evaluate a revenue-maximising park management strategy, and consider how revenues from nature-based tourism compare to those from local agricultural land-uses.