Study areas and sample collection

Samples of the Chinese egret were collected from four archipelago populations: Xingrentuo (XRT; 39°31'N, 123°03'E), Mantoushan (MTS; 30°13'N, 121°53'E), Riyu (RY; 27°01'N, 120°25'E) and Xiaocaiyu (XCY; 23°48'N, 117°45'E). Samples of little egret were obtained from two sites in China, Xinyang (XY; 32°07'N, 114°04'E) and Mantoushan (MTS; 30°13'N, 121°53'E). These offshore islands (XRT, MTS, RY and XCY) represent most of the known breeding sites of the Chinese egret across China (Fig 1). To avoid the possibility of sampling siblings, feathers or blood samples were randomly obtained from one of the nestlings in each nest. Finally, we randomly selected 20 individuals of the little egret (10 individuals per location) and 120 individuals of the Chinese egret (30 individuals per location). All of the feather samples were kept in 75% ethanol and stored at -80°C, while the blood samples were kept in 1% EDTA-Na2 at -80°C until extraction.

XRT Xingrentuo, XY Xinyang, MTS Mantoushan, RY Riyu, XCY Xiaocaiyu.