A good deal of research has recently focused on people's commitment to biodiversity conservation by investigating their “willingness-to-pay” (WTP). Because of the public's self-reported preferences for species that are more charismatic or similar to humans, conservation programs are often biased toward these species. Our study aimed to explore the determinants of WTP among 10066 participants in a zoo conservation program. The program aims to raise money to support conservation programs and involves donating a sum of money to “adopt” an animal in the zoo. We explored whether participants were influenced by particular scientific characteristics of the animal (IUCN conservation status and phylogenetic distance from humans) or by more affect-related characteristics, such as the charisma of the animal. We found that participants did not choose an animal to adopt because of the endangered status of the species, and did not donate more to endangered species than to other species. Instead, they were more likely to choose a charismatic species. However, surprisingly, those who chose a less charismatic species gave more money on average to the program than those who adopted more charismatic species, suggesting a higher level of commitment among the former. These results therefore suggest that this type of conservation program may not be an effective way of reconnecting people with conservation issues related to endangered species. We therefore advise zoos to communicate more strongly on the level of threat to species and to increase the ratio of endangered over charismatic species in their animal adoption programs. •People did not donate more to the more endangered species in a conservation program.•Charismatic species were more likely to be chosen.•Monetary donations per person were on average higher for less charismatic species.•Participants donated more money to species that are more similar to humans.