Have you ever seen birds circling around in flocks on a dark cloudy day?
In fact, this phenomenon may reflect the changing weather conditions. Both the low air pressure and high humidity will have impacts on the wings of flying insects, hampering their flying abilities and making them fly at lower altitudes and lower speed. Their predators, such as birds and bats, will then take such a good opportunity to prey on these flying insects.
In a cloudy April morning, a large flock of White-throated Needletails (Hirundapus caudacutus) swirled in the sky over the sandflat in Shui Hau, very possibly because of the seasonal changes. White-throated Needletails are uncommon migratory birds which can be found in Hong Kong. Each year, they embark on long migration journeys, first breeding in a wide region from central Siberia to Japan and then venturing to New Guinea and Australia to overwinter. They normally take Hong Kong as a staging post on their itinerary, only occasionally spotted in spring and autumn.
With their flying speed up to 130 km per hour, White-throated Needletails are among the fastest flying birds in the world! If you visit Lantau on a spring or autumn day, why not take a look up to the sky? You may be lucky enough to spot this renowned speedy flying bird.