AbstractBackgroundCaptive European bison (Bison bonasus) play an active role in conservation measures for this species; this includes education, which may conflict with these animals’ welfare. The effect of the presence of visitors on the welfare of captive animals can be negative, positive or neutral. However, the response of a given species to visitors is difficult to predict, since even closely related species display varying levels of tolerance to captivity. The aim of the study was to compare immunoreactive fecal cortisol levels (regarded as an indicator of the level of physiological stress) in groups of captive European bison that differed in terms of their social structure and the level of visitor pressure. The second aim was to determine if there was a correlation between intestinal parasitic burden and immunoreactive fecal cortisol levels.ResultsImmunoreactive fecal cortisol levels were not influenced by sex or age. However, study site and the interaction between study site and visitor pressure were statistically significant. European bison in one enclosure presented higher levels of immunoreactive fecal cortisol on weekdays than at weekends. In the other two study sites, the levels did not differ between weekdays and weekends. No correlation was found between parasitological infestation and immunoreactive fecal cortisol levels.ConclusionsMeasurement of fecal cortisol metabolites could be a valuable method for further research into the welfare of European bison in captivity. More subtle factors such as individual animal characteristics, feeding systems, and the arrangement of enclosures can be of great importance in terms of the effect of visitors on animals. The results of this study can be used in guidelines for the management of European bison populations.