Breeding success rate of waterbirds in restored wetland: an important indicator for assessing restoration effectiveness

Wetlands are crucial habitats for waterbirds, but wetland loss and degradation have caused significant population declines in many waterbird species. Ecological restoration can improve habitat quality and protect threatened waterbirds, but restoration assessments are often based on diversity rather than fitness indicators. Breeding period is a critical life history stage and breeding output affects population dynamics, thus breeding success is a fitness indicator that truly reflects habitat quality and suitability. This study evaluated the breeding performance of three ground-nesting waterbird species: Pied Avocet (Recurvirostra avosetta), Black-winged Stilt (Himantopus himantopus), and Saunders's Gull (Saundersilarus saundersi) in a restored wetland at Chongming Dongtan in the Yangtze estuary, China in 2023 and 2024. We surveyed bird abundance and monitored breeding success rates and causes of breeding failure using camera traps. Breeding success at Chongming Dongtan was further compared with published data from other sites. Results showed that the restored wetland provided nesting habitats for the three species, while the breeding success rate was low: the apparent nest success (proportion of successful nests) for Pied Avocet (2023: n = 94; 2024: n = 7), Black-winged Stilt (2023: n = 40; 2024: n = 39), and Saunders's Gull (2023: n = 109; 2024: n = 24) was 6.9%, 20.3%, and 13.5%; the cumulative nest success (estimated from daily survival rate) was 10.9%, 25.8%, and 31.6%, respectively. Nest predation was the primary cause of breeding failure for the Pied Avocet, flooding for the Black-winged Stilt, and egg cracking for the Saunders's Gull. The factors affecting daily survival rate varied among species, including breeding period, distance to water surface, local temperature, precipitation, and year. Apparent nest success of all three species was significantly lower than that reported at other breeding sites worldwide. These results suggest that although the restored wetland attracts many waterbirds to nest, it may function as a sink for the breeding bird populations. We recommend controlling nest predators, avoiding nest flooding by water-level regulation, and providing shade conditions by planting sparse plants at nesting sites. Our findings highlight the importance of using fitness-related indicators in assessing habitat quality and the effectiveness of ecological restoration.