The Crested Ibis (Nipponia nippon) is one of the most endangered avian species in the world. In 1981, seven ibis were discovered in the Qinling Mountain, central China. The ibis population responded positively to 20 years of intensive conservation growing to more than 500 birds. Population growth of the Crested Ibis exhibited a nonlinear response to increased population size along an altitudinal gradient (600-1,400 m). Prior to 1993, the ibis population was constrained to high mountains with elevations greater than 1,000 m and exhibited density dependent growth in spite of small population size (less than 20 birds). Limited availability of habitats at high elevations might result in competition for food and other resources among the ibis. The ibis returned to traditional nesting habitats at low elevations (<1,000 m) and has grown exponentially since 1992. Fledging success of the ibis did not differ between low- and high-elevation habitats. Rapid population growth of the ibis in low-elevation habitats was mainly due to increased breeding population size and reduced anthropogenic disturbances. Differences in population growth pattern along an altitudinal gradient indicate that high-elevation habitats are suboptimal. Likewise, the recovery of other endangered or threatened species may be constrained by suboptimal habitats. Therefore, caution is needed when interpreting habitat requirements of endangered species based only on presently occupied habitats.