**5. Conclusions**

Stress is currently one of the most serious problems in rearing endangered animal species in zoos and other facilities around the world. For their preservation and successful breeding, it is therefore of the utmost importance to avoid excessive stress and to provide the most suitable conditions for their life in captivity. In order for the housing conditions to be properly assessed, it is necessary to determine the impact of the factors to which captive lemurs are exposed. This study shows fluctuations in FGM levels in three lemur species likely resulting from changes in the structure of a group with relocation of individuals, construction work in the immediate vicinity of animals or placing another animal in quarters adjacent to the observed individuals. The results sugges<sup>t</sup> that some lemur species may be more or less sensitive to such disturbances. However, FGM concentrations had a similar pattern (corresponding to the occurrence of potentially stressful events) during 30 days of monitoring in all three species of *Lemuridae* suggesting that closely related animal species respond to stress load similarly. A significant increase in the FGM levels was found within one, or at most two days after the exposure to a stressor.

**Author Contributions:** Conceptualization, M.V. and Z.M.; data curation, M.V. and I.B.; methodology, M.V. and Z.M.; supervision, E.V. and V.V.; writing—original draft, M.V.; writing—review and editing, E.V., I.B., and V.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We wish to acknowledge the advice of Rupert Palme, of the University of Veterinary Medicine, Vienna. Furthermore, we would like to thank the Nature Resource Network facility operators in the Czech Republic, namely Bojana Bobi´c Gavrilovi´c and Miroslav Poljak, for making the research possible and for their help with sample collection, and Edith Klobetz Rassam and Elke Leitner for technical assistance with the EIA analysis.

**Conflicts of Interest:** The authors declare no conflicts of interest.
