Long-lived territorial bird populations often consist of a few territorial breeding adults and many non-breeding individuals. Some populations are threatened by anthropogenic activities, because of human conflicts for high-quality breeding habitat. Therefore, habitat restoration projects have been widely implemented to improve avian population status. In conjunction with habitat restoration, conservation translocations have been increasingly implemented. Adequate non-breeder survival can be a key factor in the success of these attempts because non-breeding birds may represent reservoirs for the replacement of breeders. The maintenance of breeding pair numbers is also influenced by the transition rate of non-breeders to breeders. The reintroduction of Oriental stork (Ciconia boyciana), a long-lived, territorial, endangered species, was initiated in Japan in 2005 using captive birds in hopes of increasing the population’s use of restored habitat. Our objective of this study was to elucidate the factors determining reintroduced stork survival and recruitment to the breeding populations. We estimated the survival rate and breeding participation rate by sex, age, generation, wild-born or not, haplotypes, and breeding status in storks reintroduced during 2005–2022 using Bayesian hierarchical models. There was no significant difference in survival rate between non-breeders and breeders. However, the survival rate was lower in wild-born birds than released birds, which may be related to the longer-distance natal dispersal of new generations. Accelerated habitat restoration around breeding areas and preventive measures for collision with human-built structures should be implemented for the sustained growth of reintroduced populations. A low survival rate was also detected for a specific mtDNA haplotype that accounts for the majority of the reintroduced population. This phenomenon might be explained by mtDNA-encoded mutations. Moreover, captive breeding and release history might contribute to an increase in the proportion of this haplotype in the wild.

Oriental stork observation records were collected from Hyogo Park of the Oriental white stork, which is also the repository for all observation records of ringed storks by the general public and media, as well as the home of the Inter-institutional Panel on Population Management of the Oriental white stork.