【明報專訊】The Hong Kong Bird Watching Society says there are 549 species of birds in Hong Kong, and of that number 23 species were introduced by humans. Many in this later group owe their freedom to the Japanese army. As the invaders crossed the harbour in 1941, a number of bird owners opened their cages and encouraged their pets to fly out. The sulphur-crested cockatoos, for instance, were set free from Flagstaff House and, like the offspring of certain doves, canaries, parrots, cockatiels and budgerigars, they are still here, happily multiplying in Hong Kong's welcome climate. With so many birds around, one might wonder why it's rare to see a dead one anywhere. Pigeons, for example. Hong Kong doesn't have swarms of them the way London, New York, Bangkok or Paris does, but even in those places it's rare to see a dead one. This has led a number of people to say that pigeons have been sent to earth from another planet to keep an eye on us.