Despite decades of experience in keeping lesser flamingos (Phoeniconaias minor) in zoological institutions breeding is still challenging. The continuous breeding success of lesser flamingos over many years has rarely been achieved so far. For this reason, wild captures are still needed to keep the zoo population of this species stable. The lesser flamingo is classified as "potentially endangered" by the IUCN. Therefore, it is of particular necessity to achieve a self-sustaining zoo population in order to reduce further interference in the wild animal population on the part of zoos. The Zoologischer Stadtgarten Karlsruhe has already succeeded in breeding, but the number of eggs laid, as well as the number of eggs fertilized is very low. This thesis investigates the factors influencing the reproductive success of the lesser flamingos in the Zoologischer Stadtgarten Karlsruhe. This would also allow the formulation of generally valid statements for the optimization of lesser flamingo breeding in other zoological institutions. The studies were conducted over a total period of 15 months during the breeding season in 2018, 2019 and 2020. Mating, partnering and breeding behavior was observed. Eggs laid were further incubated in an incubator in exchange for artificial eggs and examined for signs of fertilization using candling. Eggs with embryonic development were returned to the appropriate nest shortly before the calculated hatching date. Eggs without signs of embryonic development were further examined for the presence of sperm holes in the perivitelline membrane. The following conclusions could be drawn based on the results of this study. An unbalanced sex ratio has a very negative effect on reproductive success. At the beginning of the studies, there was a disproportion of 44.21 animals in favor of the male population. Unmated males massively disturbed the brood and interrupted copulations. To equalize the sex ratio females were added and surplus males were removed from the group. This resulted in a 92.4 % decrease in disturbance in 2019, within a population of 36.36 individuals. After equalizing the sex ratio, a significant decrease in this disruptive behavior was observed in 2019. After the change in group composition, new pair formation was observed. However, these did not appear to have a negative impact on reproductive success. Newly formed pairs laid fertilized eggs already in the first year of the partnership. In 2020, as many as 53.8 % of the fertilized eggs resulted from new partnerships. In contrast, the wing condition of males significantly affects reproduction. Pairs with pinioned males had 37.9 % fewer successful copulations than pairs with flying males. The 2020 breeding season took place with zoo visitors excluded due to the Covid-19 pandemic. As a result, non-breeding birds were mainly seen in the visitor area, while the breeding room, which was protected from zoo visitors, was almost exclusively occupied by animals with their own clutches, in contrast to previous years. In this season, a decrease in egg losses from 20 % to 6.4 % was observed. This shows that the zoo visitors are influencing reproductive success. During the study 99 eggs were laid. Of these, embryonic development was detected in 22 eggs by candling. Chicks hatched from 18 of these 22 eggs. Only 12 eggs were not evaluable. The remaining 65 eggs were examined in the laboratory for the presence of sperm holes in the perivitelline membrane. Sperm holes could be detected in 14 eggs. This method of indirect sperm detection was established for the first time for lesser flamingos by this work.