The Niah Swiftlets

When the Deep Skull was pulled from the ground of the Niah Caves in 1958, the newly developed technique of radiocarbon dating calculated the age of the bone to be roughly 40,000 years old, making Niah the site of the oldest homo sapien remains found in all of Southeast Asia.

The skull was unearthed by Barbara Harrisson from a dig site located just outside the mouth of the Great Cave of Niah, a site known as “Hell Trench” due to its position beneath the mid-afternoon sun.  The expedition was led by Barbara’s husband Tom Harrisson, then director of the Sarawak Museum, a venerable Sarawak institution founded by Rajah James Brooke with assistance from the great explorer-biologist Alfred Russell Wallace.  As the current Deputy Director the Museum, Ipoi Datan, and the anthropologist John Krigbaum jointly remarked in their paper, The Deep Skull and Associated Human Remains from Niah Cave:  The discovery of the Deep Skull at Niah placed the cave “firmly on the paleoanthropological map.”

Controversy remains, however.  Notwithstanding a remarkable career as soldier, anthropologist, explorer, etc., Mr. Harrisson was nonetheless not a trained paleontologist, and the soundness of his excavation techniques and a dearth of published data on the dig has called the remarkable claim of the skull’s age into question by later scientists.  The skull, as Mr. Datan explains, was not dated directly … only the strata in which the skull was discovered was subjected to radiocarbon dating.  Though recent studies have largely put these controversies to rest, the possibility that the skull was intrusive and not contemporary to the surrounding strata remains.  Such questions aside, one thing about the Niah Caves is certain:  For as long as homo sapiens has visited or inhabited the caves–and it has been a very long time–they have most likely been accompanied by the sound of swiftlets.

During my brief visit to the caves, I did not know from swiftlets.  Recorder in hand, I stood in near total darkness, on a rickety wooden walkway besplattered with shit and slippery with moss, and thought for all the world that I was recording bats.  Only later, upon my return to the States, did nagging doubts arise regarding the recordings … could the vast sea of clicks, emanating from an invisible source in the darkness above be the sound of birds?  I knew from my embarrassingly hasty examination of the cave history presented at the park entrance that a certain species of bird did in fact inhabit the cave but to this I paid little attention (for I was anxious to walk around in a cave).  My lazy mind just assumed it was bats flitting about above me–I was in a cave, after all.  In time, however, curiosity prevailed over mindless assumption and a few months after my return home I emailed audio files to Liz Price, a Malaysian cave expert I had tracked down online (  The very next day a gracious response informed me that no, what I had recorded was not bats, but rather swiftlets.  More accurately:  The predominant clicking sounds heard on the files were produced by swiftlets.  Deeper in the recorded mix there was in fact the sound of bats chattering amongst themselves, but the most prominent and distinct of the sounds–the clicks–belonged to swiftlets.

These remarkable sounds are calls utilized by the bird to echolocate.  Like a bat, a swiftlet will listen to the echo produced by his or her own click and with this information the animal is able to map and safely maneuver through its immediate environment without visual input.  Though it is an ability shared with bats, the swiftlet calls differ from the high-frequency calls produced by bat echolocation in one vital characteristic:  The swift call is within a frequency range a human being can hear.

Three species of the little bird inhabit Niah.  One of these, the Black-Nest Swiftlet, produces a much sought-after item:  An edible nest.  Unfortunately for the bird, commercial trade in these nests has evolved into an enterprise sufficiently large and complex enough to place Niah firmly on the regional economic map.  Not surprisingly, the harvesting of swiftlet nests–both legally and illegally–has contributed to a decline in the bird’s population.  The local palm-oil industry may also contribute to swift travails, as the local rainforest, where both birds and bats feed, is being replaced with an agricultural monoculture maintained in part by pesticides, and the healthy diversity of edible insects once present is being replaced by a depleted and/or poisoned stock of creatures.

Producing exact numbers regarding the percentage of species decline is difficult and figures vary from study to study.  Nonetheless, population decreases appear to be substantial.  A study done by SLUSE (the University of Copenhagen’s Sustainable Land Use and Natural Resource Management program) in 2001 cites studies showing the number of swiftlets dropping from 1.7 million in 1935 to roughly 150,000 in the mid-1990s.  While the bird has since shown signs of recovery, the wash of animal sound I experienced in the first decade of the 21st century, impressive though it was, undoubtedly paled in comparison to the overwhelming sonic experience which must have greeted visitors to the cave only a few decades before.

Following is a recording I made in 2008.  It is actually two different recordings that I somewhat awkwardly cobbled together.  The first half was made not far from the mouth of the cave and it gives the listener an idea of the general hubbub produced by large numbers of swiftlets and a handful of bats; the second half was recorded deeper in the cave, in a less populated area, and features both a single swiftlet echolocating its way around in the dark, as well as some loud, encroaching humans.


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