BIRD WHOSE SALIVA IS DELICACY
Cave swiftlets belong to the genus Collocalia which covers 21 species, found in SE Asia, Australia, Pacific and Indian Ocean islands, Seychelles and Mascarenes. In China saliva of these birds is a delicacy and is used for making bird’s nest soup, locally known as ‘Dragons Teeth’, though scientists claim these nests have no nutritional value and their soup has no taste but locally nests are regarded as highly aphrodisiac.
Grey-rumped swiftlet (Collocalia francica), another species of cave swiftlets, is the most prized bird for making nest soup because its nest are made of pure saliva and do not require extensive cleaning. The quantum of the business of these nests can be understood by the fact that in one year alone, over 35 lakh (3.5 million) nests were exported from Borneo to China.
These birds build their nests on the walls of dark caves and high ceiling, up to 1,500ft from the entrance. Nests are made up mostly of their saliva and feathers and are delicacy in China. Since nest collection is a very hazardous job hence it fetches a handsome price. Some years back single nest used to cost 4 to 5 (Brit.) pounds. Collectors use ladders and ropeways which can be even 400ft high.
Flying in complete darkness of caves, swiftlets use echolocation, by producing series of clicks, to orientate and navigate. Echoes, thus created, reflect from the sides of the cave walls and enable the birds to find their way. Each click consists of a burst of pulses, the separation of which cannot be appreciated until the call is analyzed spectrographically. These birds hunt for insects by day and return to their caves at night. Their capability to echolocate apparently allows them to stay out for a longer period of time after sunset, and to set out before sunrise, giving them a chance to exploit larger areas of food reserves than it would be possible, if they were using vision alone.
One species, Uniform Swiftlet (Aerodramus vanikorensis) produces pair of echolocation clicks, which are found to be between 4,500 Hz and 7,500 Hz, not sufficient to provide detailed information about the environment to the bird, but still, according to the results of various experiments, it provides ample information to enable the bird to avoid wires of 6mm diameter in complete darkness.
These birds are classified under the family Apodidae to which both swifts and swiftlets belong. Family has about 12 genera with approximately 80 species, found worldwide. They are small to medium sized birds with short, small bills and a wide gape. They are highly aerial, fast-flying, insectivorous birds, usually catching prey on wings. Wings are long, curved, and narrow. Tail is short and often spine-tipped. Swifts have weak, short legs with reversible hallux. They build their nests in caves, buildings, on trees and rocks, often using their saliva.
Birds without legs????
The word Apodidae means ‘lacking legs’. This is nearest to the truth for these birds. Swifts have species with the shortest legs in the avian world. In other words legs are virtually non-existent and superfluous. In some species only the feet are visible outside their feathers. Swifts have strong claws for grasping vertical surfaces when breeding or sometimes for roosting. There is a misconception that they have all four toes permanently pointed forward.
Reason behind their short legs is they are highly aerial and rarely come on to the ground. Perhaps no bird spends more time in the air than this small creature. For their highly efficient flying they have long wings and a low body mass in relation to wing area, and bear short, shallowly forked tails that reduce drag and increases lift. Their long pointed wings enable them to spend less energy on supporting their body-weight in the air. With such a fine-tuned body swifts are about 70 per cent more efficient flier than other birds of their size and weight.
Sunglasses for birds !!!!
For every skydiver it is necessary that he or she should wear sunglasses specially when diving so that eyes can be protected. Same is true with swifts, they too wear ‘glasses’ in the form of transparent eye membrane which not only enable them to see while the ‘veil’ is on, but also acts as windscreen wiper, removing irritating particles with every blink. They also have a thick fringe of feathers round their eyes that look like eyelashes and guard their eyes against insects that may strike them.
Since these birds cannot land on the ground easily because of their short legs, collecting nest-building material from the ground, like the other birds do, is almost impossible for them. Hence they tend to use materials they can obtain on the wings. The chimney swifts, for example, snap off twigs as they fly.
All swifts and swiftlets use their saliva to make their nests. While some use it for the gluing of nest-building material together, like mosses, feathers and twigs, others, specially cave swiftlets, build their nests entirely from saliva. The salivary glands of these birds enlarge as the breeding season approaches enabling the bird to produce large amount of ‘cementing material’ – their saliva. When it comes to constructing a nest both male and female take part in it. They fly straight at the wall or ceiling, often without benefit of ledge or cranny, touching it briefly with their tongue to deposit a tiny blob of sticky and thread forming saliva before veering away. In this way they slowly build up a rubbery U-shaped strip, which hardens slowly with the passage of time. Birds keep on adding their saliva to it until a pocket is formed to place eggs.
Swifts and nightjars (family Caprimulgidae) have the smallest bills in the world of birds. When it comes to comparison between the two nothing can be said with confidence which one of them possesses the shortest bill in absolute terms. Both the birds are wide-gaped and pursue insects on wings.