As any experienced bird ringer will tell you, there are certain species which become active very early in the morning, often at the first hint of daylight, which if trapped are frequently among the earliest birds trapped on a given morning. In Hong Kong notable examples are chats, thrushes and Lanceolated Warbler, and I'm saddened, but not surprised that these are well represented among the birds affected by the noise barriers. The problem is that these birds move around in such low light levels that black bird stickers are probably effectively invisible at that time and will not resolve the problem.
