Birds like flycatchers, warblers, egrets and herons can move back slightly using the fluttering method--but the only bird that can actually fly backwards without relying on the wind is the amazing hummingbird.

Some swiftlets, appropriately named edible-nest swiftlets, build nests almost exclusively from their hardened saliva. In China, the saliva nests are used to make bird's nest soup and are one of the most expensive foods in the world, despite having little flavor and no real nutritional value.

The largest known bird's nest was built by a pair of bald eagles near St Petersburg, Florida, USA and measured 2.9 m (9 ft 6 in) wide and 6 m (20 ft) deep. It was examined in 1963 and was estimated to weigh more than 2 tons (4,409 lb).

The yellow-bellied sapsucker (Sphyrapicus varius) is a medium-sized woodpecker that lives on a diet of tree sap, insects, and berries. The sapsucker can be found in Canada and the Eastern United States. During the winter, it migrates to Central America and the West Indies.

Native to New Zealand, kiwis are a bizarre, land-bound bird. Scientists, mystified by the kiwi's strange properties--which include feathers that feel like hair, heavy bones filled with marrow, and nostrils on the tip of their nose (rather than on the base of their beak like most birds)--have sometimes called them "honorary mammals".

You can find plenty of penguins in Antarctica, but there are no penguins living at the North Pole or any other part of the Arctic. In fact, the birds live almost exclusively in the Southern Hemisphere.

The rapid pecking causes a woodpecker's skull to heat up, which is why they often peck in short bursts with brief breaks in between, giving the head some time to cool down.

According to a survey conducted by the RSPB (Royal Society for the Protection of Birds), the most commonly sighted bird in the UK is the house sparrow. Around four of them appeared in each garden.

A budgie named Puck holds the world record for the largest vocabulary of any bird at 1,728 words.

In addition to hoots, owls may chirp, whistle, scream, screech, bark, growl, shriek, hiss, or even whinny. Scientists call these different sounds vocalizations.