Recovering a species to thousands of individuals after a catastrophic population decline seems like a success. Yet behind the numbers lies a subtler reality: the genetic legacy of a narrow founding and the specifics of reproduction can limit a population's viability for decades.
The Japanese crested ibis (Nipponia nippon) underwent a sharp decline in the 20th century due to habitat loss and pollution. In 1981, only seven wild birds were found in China's Shaanxi Province — two breeding pairs and three chicks. Since then, conservation programs, including captive breeding and reintroduction, have allowed the population to exceed nine thousand individuals in a little over four decades.
A study published in Nature Communications in February 2026 showed that success depended not only on numbers. Endogamy, inevitable with a small number of founders, reduces chick hatching success. Modeling of 300 scenarios confirmed that in most cases the population reaches its target, but the speed and resilience depend on the species' initial demographic parameters.
It is especially important how reintroduction is organized. Creating several new groups at once from a large recovered population yields better results than sequential "budding off" from recently founded colonies. Increasing the number of founder pairs accelerates growth and slows the accumulation of inbreeding; when only three pairs are used, the risk of collapse is markedly higher.
Thus, a simple count of individuals does not reflect the true state of a species. The history of genetic diversity, the number and origin of founders, and the biological characteristics of reproduction and survival determine whether a population will be able to remain resilient in the future or will again find itself vulnerable.
For conservation programs, this means the need to consider not only population numbers but also genetic structure when planning reintroductions and monitoring.
