Abstract:Understanding the distribution of potential breeding habitat of endangered birds is critical to formulating effective protective measures. The crested ibis (Nipponia nippon) had been critically endangered, and currently its population is rapidly recovering. A predictive breeding habitat distribution map of this species was estimated using the Maxent model with a total of 125 recorded nest points and 9 environmental factors. The distribution of potential breeding habitat and its relationship with major environmental factors were analyzed with Maxent 3.3. Accuracy of model’s result was evaluated with area under ROC (AUC). Importance and contribution to model’s prediction of environmental factor was evaluated with Jackknife. The distribution of suitable habitat was indicated with habitat suitability index (HSI). The habitat of HSI > 0.5 was considered to be fundamental suitable habitat for ibis, HSI > 0.6 was moderate suitability, HSI > 0.7 was high suitability. Results of Jackknife test showed that four variables including elevation, brightness index, slope, and green vegetation index had the greatest effect on habitat selection, with a contribution of 38.1%, 18.3%, 16.4% and 14.3% respectively (Fig. 2). The overall preferred elevations were 500 – 1 200 m (Fig. 3). The preferred lowest elevation was obviously lower than the value (800 m) of the former studies. Brightness index indicated that the area of suitable habitat decreased with degree of bare ground increasing. Suitable habitat was significantly negative correlation with slope. Green vegetation index indicated that suitable habitat was mostly distributed in the moderate vegetation coverage area (Fig. 3). Results showed 1 706.58 km2 of crested ibis breeding habitat of suitability threshold of 0.5 (955.88 km2 and 437.89 km2 for thresholds of 0.6 and 0.7, respectively). Larger suitable habitat patches (area > 15 km2, HSI > 0.5) were most distributed in the Yangxian county, Chenggu county and Xixiang county (Fig. 4). Area of suitable habitat for ibis was most in Yangxian county (491.24 km2, HSI > 0.5). It was also in the Chenggu county, Xixiang county, Nanzheng county and Ankang county that area of suitable habitat was bigger than 100 km2 (HSI > 0.5, table 1). It was in the Hanyin county, Mixian county and Shiquan county that area of suitable habitat was bigger than 50 km2 (HSI > 0.5, table 1). Results indicated that there was enough breeding habitat to satisfy crested ibis dispersing and reintroducing.