The Most Delicious Nest

Swifts are amongst the fastest birds, and even if they resemble swallows, they are in fact related to hummingbirds. A swift weighs a few tens of grams, but with its sickle shaped wings they can reach 160 km (100 mi) per hour.

Swifts are the birds the term aerial suits best as they catch food (insects), eat, drink, collect material for the nest and even mate (this is unique amongst all birds) while in the air! They can even sleep during a floating flight and can remain in the air 9 months annually. Ancient people even thought they nested in the sky...

The crescent wings are especially designed to eliminate air resistance during the flight, increasing speed by alternating rapid and short wing beats with short floating flights. Swifts are able to beat one wing faster than the other and this slight di-correlation enables them to make sudden turns during the flight without reducing speed. This way they can rotate rapidly in the air mouth wide open catching insects. And they have to eat a lot, as they make hundreds of kilometers on a daily basis.

But these dull colored birds are not famous because of their way of flying, but rather because of the nest of some tropical species. They have a very unusual nest material: their own saliva. Special salivary glands produce large amounts of saliva that acts like a binding element for the materials from which the nest is made.

The swifts have such reduced feet that they almost never descend on the ground nor can they stay perched on branches, like other birds. Their tiny feet, like hooks, are so small that the bird cannot rise high enough to execute a complete wing beat. But these feet are ideal for clinging on vertical surfaces like rocks, cave and building walls. When swifts have to build their nests, they cannot collect twigs or mud from the ground, like the other birds nermally do.

The chimney swift (Chaetura pelagica) from North America harvests twigs while flying rapidly amongst the branches of a tree, strongly catching a twig and breaking it off because of the inertia. The twigs are glued together and cemented by the viscous saliva on a vertical surface. American palm swift (Tachornis) catches hairs, feathers, cotton pieces, and other light materials floating in the air, which they are used afterwards in building the nest making use of the same technique.

In the case of the African Palm Swift (Cypsiurus parvus), the nest is built by a small cushion of feathers stuck with saliva on the downside of a palm leaf. The nest is also exposed to winds, so how does the egg remain in the nest? The egg too is glued to the nest with saliva. The hatchling grabs strongly to the wind exposed nest.

Another group called swiftlets or cave swifts, encountered in southeastern Asia and Pacific islands, builds the nest almost entirely from hardened saliva. These are the famous comestible nests, the main ingredient of the Chinese "bird's nest soup". Millions of nests are harvested annually in order to make this delicacy and in Philippines, for example, families possess nesting walls or rocks, which they transmit from generation to generation. Such nests are among the most expensive animal products consumed by humans. When dissolved in water, the nests get a gelatinous texture. Yummy! Bird saliva! In Hong Kong a bowl of this soup costs between US $30 and $100.