About 10 years ago, two scientists decided to estimate the total number of birds on the planet. The number they came up with was 200 to 400 billion individual birds.
I think that this is one of the loveliest birds of Hong Kong. 普通翠鳥 . Common Kingfisher . Alcedo atthis -
That is a lot of birds....BUT... bird numbers have been declining both in terms of species numbers (by about 500 species) and numbers of individuals (by about 20-25%). This decline is due to human activities, such as the cutting down of forests, contamination, invasive species (like cats) , and climate change.