Many shorebirds rely on sandy beaches to breed. However, these ecosystems are rare and unstable on the Guianas coast because of sediment dynamics. Nonetheless, they host 2 shorebirds that breed in the Nearctic and the Neotropic: Wilson’s Plover (Charadrius wilsonia) and Black-necked Stilt (Himantopus mexicanus). We studied their breeding biology in the Amana Nature Reserve, a Ramsar Site in French Guiana, on sandy beaches bordered by brackish lagoons during 1 breeding season. From early June to late August 2008, we located and monitored 19 Wilson’s Plover and 15 Black-necked Stilt nests. Most nests were associated with bare ground. While stilts preferred to build their nests with twigs closer to lagoons, plovers did not show any preference in nest location and composition. For plovers and stilts, clutch sizes were 2–3 eggs or 3–4 eggs per nest, respectively, and the mean egg volumes were 12.1 ± 0.4 cm3and 20.6 ± 0.6 cm3, respectively. The apparent hatching success for both species was low, 11% for Wilson’s Plover and 13% for Black-necked Stilt, whereas daily nests survival was high for both species. Clutch sizes, egg dimensions, and egg colorations were comparable to those described elsewhere, but the breeding season started later than at other localities for the Wilson’s Plover. In French Guiana, the apparent nest success values for both species were much lower than those reported in the United States and the West Indies but seemed slightly higher than in Brazil. Human activity impacts were limited in our study area and did not explain the low nest success values found. Beach flooding at high tide was the main cause of clutch failure, followed by predation. Ironically, flooding allows the maintenance of this low, open, and debris-covered habitat used by beach-nesting shorebirds.

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