The Nam Sang Wai developer has claimed its proposed project would almost meet the "no-net loss" principle under planning guidelines that require wetlands to retain the same net area after development. The project would lead to a direct wetland loss of 18.6 hectares but about 13.8 hectares would be re-created by altering existing ponds or removing the banks between ponds, the developer said. The reduction would also be partly offset by improvements to fish ponds at Lut Chau, north of Nam Sang Wai, which is proposed as a reserve, resulting in a total net loss of three hectares. The developer also claims the project will improve the ecological function of 112 hectares of wetland by 30 per cent, through active management such as regularly draining ponds to attract birds. But WWF Hong Kong conservation manager Alan Leung Sze-lun said the developer might have underestimated the wetland's size and therefore the amount of net loss. "We suspect that some wetland areas might be mistaken as terrestrial grassland in their study," he said. The developer estimates the combined wetland size of the two sites at 135 hectares, while about 42 hectares is regarded as non-wetland. According to an ecological assessment, at least 40 per cent of bird species - 54 of 130 - recorded in the development site at Nam Sang Wai are of conservation importance, while 33 of 82 species at Lut Chau are also of importance. But the assessment proposes that detailed conservation plans be drafted for only 16 species, including the black-faced spoonbill and red-billed starling. The bent-winged firefly, which is unique to Hong Kong and was first found at the Wetland Park in Tin Shui Wai in 2009, has not been found at the site. It was, however, recorded in four surveys during the summer in mangroves near Lut Chau and on the periphery of Nam Sang Wai.