Spot the million dollar cottage industry

Can you spot the multi-million-dollar industry in this picture? And have you ever fancied eating a bird's nest? For centuries Chinese royalty have relied on eating the salvia from swifts, collected from their nests (hence the name), for its assumed health properties. Those nests used to fetch a very high price as the collection was very cumbersome. Today the high price has remained, what has changed is the collection. Ingenious Asians have figured out how to attract swifts through electronic sounds. Nowadays they position loudspeakers in apartments with small windows. The sound proves to be irresistible for the birds and they start nesting in the apartments (shown in the picture). According to a local source in Malacca, where this picture was taken, one apartment can generate revenues of USD 150'000 a year or higher. No wonder that the apartments are heavily guarded. The booming trade in bird's nests has even led to the formation of various trade associations.