Top 100 Birding Sites of the World

Information

SITE RANK

HABITAT Cave system, forest

KEY SPECIES Edible-nest, Black-nest, Mossy-nest and Glossy Swiftlets; Bat Hawk, Rufous-bellied Eagle, Peregrine Falcon, forest birds

TIME OF YEAR All year round

The caves have a population of one million bats, ensuring an abundant food supply for the attendant Bat Hawks.

There can be few more insalubrious surroundings for great birding than within the Gomantong Caves, on Sabah on the island of Borneo. It is dark, except for 20 minutes around noon when shafts of sunlight pierce the main chambers from above. It smells appalling, the result of countless years of guano accumulation on the cave floor. It is unwise to look up, for fear of being pelted with new supplies of that same guano. And should you stray off the paths, you could find yourself knee-deep in the deposits, with thousands of cockroaches, long-legged centipedes and other leggy invertebrates for intimate company.

What a place, though! Within these huge caves of cathedral-like proportions and all-enveloping hush, there is a special ecosystem. The cave ceilings provide habitat for about one million Sheath-tailed Bats, and for approximately the same total number of swiftlets, of which four species breed. The caves also form the basis of a major human industry, that of collecting the nests of the swiftlets to make bird’s-nest soup.

The swiftlets are not much to look at, being essentially featureless dark brown, but they are extraordinary. For one thing, they possess the ability to find their way about by echolocation, one of only two groups of birds to have evolved this ability (the other is the Oilbird). This is the technique that bats use, but the swiftlets are less sophisticated, using it mainly for manoeuvring about the cave system, and much less, if at all, for catching mobile food. The clicks they produce are perfectly audible, sounding rather like a high-pitched trill or rattle, as if one was running a finger along the teeth of a comb, and they punctuate the silence of the caves when the birds enter or leave the caves at dusk and dawn.

The other remarkable aspect of these birds’ lives concerns their celebrated nests. Each species builds its own particular type, each out of slightly different materials. The Glossy Swiftlet is rather the odd one out, making its nest out of plant material merely fixed to the substrate by saliva; these swiftlets cannot echolocate and build only on well-lit sites outside the main caves. The Mossy-nest Swiftlet makes a nest out of small pieces of vegetable matter, the entire structure glued together by saliva; the nest is not rigid so, unlike the other swiftlet nests at Gomantong, cannot be fixed to a vertical surface. The Black-nest Swiftlet’s nest is a bracket-shaped structure made out of translucent saliva mixed with feathers, and the famous Edible-nest Swiftlet’s nest is made of nothing at all other than saliva, and tends to look whitish in the torchlight.

The making of bird’s-nest soup is an enormous industry, probably the single most commercially valuable business worldwide that depends completely upon a wild bird. It is worth well over US$1 billion a year and is increasing. At the same time, hardly surprisingly, the swiftlets are declining in those areas where their nests are harvested unsustainably (often, appallingly, when there are eggs or young in the nests). At Gomantong Caves, however, the collection is regulated; the caves are managed by the Wildlife Department of the government. Only two collections a year are permitted, one between February and April, just after the birds have built their nests but not laid any eggs, and then again between July and September when breeding, with the newly-built nests, has been completed.

It is a gripping experience to watch these collections taking place in the lofty heights of the cave. Small groups of men reach the cave tops using rickety rattan ladders, ropes and poles that look as though they might snap or snag at any moment. The nests are gathered in minute rattan baskets by the assigned collector. The nests may be gathered anywhere between 30–90 m above ground, in semi-darkness, at great personal risk. Watching it is heart-in-the-mouth stuff. The rewards are high for the owners, however, as 1 kg of Edible-nest Swiftlet nests – about 100 nests – can be worth US$1,000 or more.

If you visit these caves, make sure that you remain until the evening. This is when there is a vast mêlée around the caves, as the whole community swaps shifts. The bats stream out of the caves for the night’s feeding in seemingly never-ending waves, and a little later the swiftlets return from their foraging in the twilight skies above the forest. This rush-hour makes for an impressive spectacle, especially in the surroundings of the remarkable limestone Gomantong Mountain.

Not surprisingly, the hordes of small flying bodies attract predators. These include some quite unlikely hunters, such as the Rufous-bellied Eagle, which makes a clumsy grab as it flies awkwardly through the swarm, as well as the more professional bird-catchers such as the Peregrine Falcon, which is swift and decisive. However, the most impressive and expert hunter of these masses is the Bat Hawk, with its long, pointed, falcon-like wings. This highly specialized species, whose main daily foraging period lies in the half-hour around dusk, flies with leisurely, powerful wing-beats as it approaches the flocks, but then, having selected its prey (bat or swiftlet), suddenly accelerates and, if necessary, twists and turns so that it can grasp its quarry from behind and above. Prey is quickly transferred to the bill and swallowed whole, so that the Bat Hawk can carry on feeding while flying; it may be only a minute before it kills again. One Bat Hawk was seen to catch 17 bats in a single session, a pretty useful evening’s work. At any one time there may be three or four individuals working the caves and sharing the airspace.

It should be mentioned that, exciting though the caves are, the surrounding forests are by no means lacking in wildlife, and the whole area deserves a few days’ exploration. The Gomantong Forest Reserve is a good place for Orang-utans, and Proboscis Monkeys can be seen along the nearby Kinabatangan River.

Harvesting nests is a dangerous job – here the collectors are making their preparations.

The entrance to the caves is quiet during daylight hours but becomes a busy throughfare for swarms of swiftlets and bats at dusk.

Looking down on the whitish nests of the Edible-nest Swiftlet, which are made entirely out of the birds’ saliva.