Abstract:[Objectives] The White-faced Plover (Charadrius dealbatus), once a subspecies of the Kentish Plover (C. alexandrines), was identified as an independent species in 2016 and included in the IUCN Red List of Threatened Species concurrently. To date, little is known about its reproductive behavior. The aim of this study is to enrich the basic data of the White-faced Plover by observing and describing the nest site selection and reproductive behavior of the White-faced Plover. [Methods] The study was conducted in Shanxinsha Island, Qisha Town, Fangchenggang City, Guangxi Zhuang Autonomous Region (March to July, 2019 and 2020) (Fig. 1). For the nest selection, we interviewed local photographers and fishermen. The breeding situation in 2019 and 2020 is shown in Table 1. We select 3 nests of White-faced Plover for observation every year, and morphological parameter (length, width and depth) and clutch size of each nest, and size of each egg in every nest were counted and measured. After nest selection, the behavior of the target nesting male and female White-faced Plovers during the breeding season was recorded and described using the target animal sampling method; the behavior of White-faced Plovers during the breeding season was counted as a percentage of the total time observed using the all-event sampling method, and when other behaviors resulted in vigilant calling by non-target parents were also recorded together. The time spent at the nest by both sexes was analyzed using a t-test, with significant differences set at P < 0.05, and analyses were completed by SPSS 23.0. During the observation period, male and female adults were distinguished by their breeding plumage: males had brightly colored breeding plumage with a dark brown neck stripe and a bright orange crown; females had dull colored breeding plumage with a light brown neck stripe and a reddish brown crown (Fig. 2). The observation time was from 7:00 to 19:00, and was recorded by infrared cameras at night. [Results] We found that the selection of nest site was mainly determined by intertidal elevation, which were mostly located on the beach or open gravel fields that was not submerged at high tide level. The selection of nest site needed 3﹣7 days generally (n = 6), and their nesting behavior mostly occurred after sunset. There were two nesting patterns: 1) Shallow pits on the beach or open gravel fields, which were mainly paved with stones and shells (Fig. 3a); 2) nests built on the beach with sparse vegetation litter or human wastes (Fig. 3b﹣d). Space among nests were usually not less than 150 m (n = 6). The length, width and depth of nests were 10.4 ± 0.6 cm (9.8﹣11 cm), 7.7 ± 0.1 cm (7.6﹣7.9 cm), and 3.6 ± 0.1 cm (3.6﹣3.7 cm) (n = 6), respectively. The female lays 1 egg per day, usually three to four eggs per cluster (n = 6). The eggs had a pale yellowish base with dense brown patches. The long and short diameter of these eggs were 33 ± 0.3 mm (32.4﹣33.4 mm) and 24.5 ± 0.1 mm (24.4﹣24.5 mm) (n = 21) respectively. Additionally, females spent more time on raising offspring than males (P < 0.01) (female: 582.5 ± 22.6 min, male: 428.8 ± 30.2 min) (Fig. 4). The incubation time for each nest was 28 ± 2 days (n = 6). When the incubation process finished, the nestlings would peck and break the shells, this process could last 18﹣28 hours (n = 21). After the down feathers are dry, they could run fast immediately (Fig. 6a﹣d). Different from Kentish Plover, these nestlings were raised by both females and males. After comparison with Kentish Plover, it found that White-faced Plover mostly nested in light beaches and gravelly areas that were not flooded by water at high tide, and were less dependent on trees and shrubs; Kentish Plover mostly nested in gravelly areas, salt flats, wetlands and bare saline areas with sparse alkali canopies (Suaeda glauca) that had some shade, and rarely chose light beaches as nest sites, and nesting materials were different due to different nest sites; and there were some differences in the time allocation of incubation period. Female White-faced Plovers left the nest for a shorter period of time during daytime incubation, while female Kentish Plover left the nest more frequently, and after the juveniles were able to move, most female Kentish Plover would abandon their families and look for their next breeding partner, with the male looking after the juveniles, while White-faced Plovers were mostly two-parent broods. [Conclusion] The results of the study could not only advance our understanding of the breeding behavior of the White-faced Plover, but also provide first-hand information regarding the ecological habits of the White-faced Plover.