HFCheung

I think Chinese Bulbul have been spreading north, and they are now much more common in Northern China.  The effect is that (I guess) the density of birds in South China (including HK) has been going down a lot, by at least 50% I guess.  Now Red-whiskered Bulbul is more abundant than Chinese Bulbul in most places in HK.

Similar decrease in population density in HK also happened to Great Barbet, Black-crowned Night Heron, Cattle Egret, Black Baza.