Abstract: The reintroduction efforts for the crested ibis (Nipponia nippon) have been hampered by a population bottleneck, leading to low fertility rates and poor chick survival during artificial breeding programs. This highlights the urgent need for molecular-level research into their immune mechanisms. Among these mechanisms, defensins are critical immune effector molecules that play a key role in antibacterial defense and environmental adaptability. However, there is a notable lack of research on the expression of β-defensin genes in crested ibis populations. To address this gap, we investigated β-defensin gene expression using peripheral blood samples from 74 crested ibises housed at the Xiazhuhu Crested Ibis Breeding Center in Deqing, Zhejiang Province. The expression levels of 11 β-defensin genes were measured using real-time fluorescence quantitative PCR, focusing on the widely expressed genes AvBD1α, AvBD2, AvBD3, AvBD4, and AvBD7. The analysis revealed the following key findings: 1. The relative expression levels of the five widely expressed AvBD genes were significantly and positively correlated with one another. 2. The relative expression levels of AvBD genes were higher in young birds compared to subadults and adults, suggesting that these genes play a crucial role in the growth, development, and environmental adaptation of young ibises. 3. The expression levels of AvBD genes showed moderate to high positive correlations between parent and offspring birds. These findings provide valuable insights for identifying individual crested ibises with robust immunity and hold practical significance for forming rewilding populations to support conservation and reintroduction efforts.