Hong Kong has a list of over 550 recorded bird species. A high proportion of them are winter visitors and passage migrants, followed by resident birds; there are comparatively few summer visitors. The best time for watching birds is between September and May.
| Spring and Autumn migrants | (46%) | These species pass through Hong Kong during their northward or southward migration. |
| Winter visitors | (25%) | Visitors which arrive in autumn and leave in spring. |
| Residents | (11%) | These species spend the whole year in Hong Kong. |
| Summer visitors | (4%) | Visitors which arrive in spring and leave in autumn. |
| Others (Vagrant and Occasional Visitors) | (14%) | Species which visit Hong Kong occasionally, in some cases apparently as vagrants. |
Migration is a type of adaptation shown by animal species (including birds) to their living environment, weather, species population and density. It is a process which enables a species to search for alternative food supplies , increasing its chance of survival and its ability to take care of the next generation in a more suitable environment.
At higher latitudes in the northern hemisphere, food is more abundant during spring and summer. However, food items such as insects and berries become increasingly difficult to find when the weather becomes cold in autumn, and extremely cold during winter. Millions of birds migrate from their northern breeding grounds in Siberia and northeast China to warmer in the southern areas (e.g. southern China, southeast Asia, Australia and New Zealand) where they spend the winter. They then return to their breeding grounds in early spring between March and May. Such birds are known as migrants.
Birds show different migration patterns: breeding grounds, breeding period and migration routes vary among different species. Acting out of instinct, birds are able to traverse immense natural barriers between breeding and wintering grounds. They frequently migrate in groups and make one or more stopovers en route to refuel. Some waterbirds and seabirds can achieve journeys of 29,000 km in one year! Hong Kong is an important stopover station or wintering ground for many migrants.
Migrating birds consume huge amounts of energy. Fat stored under the skin and internal organs is the main source of this energy. Successful migration depends on a number of factors, including ability to find suitable habitats, resource availability (food, water and shelter, in particular) and favourable environmental conditions (temperature, rainfall, predators and competitors, etc).
