Why 2 Birds in the Hand May Be Better Than a ?Hobbit? Skull (in a Cave Deposit, at Least)

Labeled bags of bones

The light flickers, and then goes out. The humming of the air conditioning stops. The sounds of Jakarta?s hustle-bustle and infamous traffic gridlock slowly seep into the room, softly lit by the glow of my laptop screen. It?s a late October afternoon, the rainy season started a few days ago, and I?m at the National Research and Development Centre for Archaeology in Jakarta, Indonesia. On the table in front of me, now only dimly lit from my laptop screen, lies a cast of a famous human skeleton. Carefully arranged on a fine layer of black velvet, these pieces represent Homo floresiensis, the enigmatic hominin species from Liang Bua cave on the Indonesian island of Flores.

Excavation in progress

The discovery in 2003 of Homo floresiensis, affectionately referred to as a ?hobbit?, took scientists worldwide by surprise, and challenged many things thought to be understood about human evolution. Intense scientific debates followed about the validity of Homo floresiensis and its status as a separate species, and many of these debates continue to this day. Behind the black velvet covered table, however, stacked up high against the walls, are hundreds of boxes and plastic containers, each of which contains evidence of the other animals that lived and died among Homo floresiensis. I can?t help but think that these boxes and containers, not the skeleton on the table, will help us to better understand the rise and fall of Homo floresiensis.

Liang Bua interior

Liang Bua is a limestone cave in western Flores, located on the southern slope of a lush green valley that over time has been cut down by the Wae Racang river. Its sediments have yielded an enormous number of animal bones, and despite its star status, ?hobbit? remains are hugely outnumbered by the remains of other animals, such as rats, pygmy elephants, Komodo dragons, bats, and most importantly in my case, birds. My first encounter with the ancient birds of Liang Bua was in 2006, when I made my first trip to Jakarta. Coping as best as I could with the heat (I?m northern European after all), I spent my days carefully unwrapping tissue paper only to find bird bones, some very large, most of them small, tucked inside. I couldn?t help but feeling a bit overwhelmed when I left Jakarta.

Now, several years and many trips to Jakarta later, the birds from Liang Bua are speaking, figuratively at least (technically, parrots may talk but they and others make sounds). And their story is fascinating! Although bird remains probably make up only about 1% of the total number of animal bones excavated from Liang Bua (which is a lot more than the hominin bones by the way), they are consistently present from the top layers of sediment all the way down to the bottom of the cave. On top of that, the birds are incredibly diverse, which means that the ?hobbits? lived in a world full of birds. The nearby forests were home to pigeons, parrots, small owls, and goshawks. A barn owl probably roosted at the eastern cave wall next to the entrance.

Further back in the cave, swiftlets nested high up against the wall in the dark crevices. When I visited Liang Bua in 2011, I was so excited to see living swiftlets darting in and out of the cave like acrobats. I had been looking at the bones of these birds for months, but I fell in love with them as they gathered above the forest canopy in the late afternoon to feed on insects. Fossil swiftlet bones, which are found as deep as 9.5 m, show that these tiny birds have been doing this for tens of thousands of years. They own this place.

River valley in the Liang Bua area

Throughout prehistory, occasional overflowing of the nearby Wae Racang river likely created marshy and muddy areas that were excellent feeding grounds for all kinds of water birds, including snipes, plovers and sandpipers, probing and prodding the mud with their long bills in search of food (invertebrates mostly). Brahminy Kites patrolled the river for fish or hung out near the mouth of the cave, waiting for a fly-by bat or swiftlet snack. Kingfishers and small rails could be found in the woodlands close to the river, while little buttonquails scurried around in the drier grasslands higher up.

Despite this seemingly peaceful setting, life at Liang Bua wasn?t all peachy. The remains of multiple individuals of giant marabou storks and vultures illustrate a darker side of Liang Bua. Carcasses of pygmy Stegodon (an extinct relative of elephants), probably brought into the cave by Homo floresiensis (Morwood et al., 2004, 2005; van den Bergh et al., 2009), must have attracted the attention of these fierce scavenging birds.

Their modern-day counterparts, the African marabou storks and vultures, have a love-hate relationship. Marabou storks signal that it is safe for vultures to approach a carcass, helping them in their quest for food. But, as their massive straight bill is poorly equipped for tearing off chunks of meat, they then often resort to intimidating vultures to drop their chunk, or even steal the meat directly from them. We can only imagine what the scene at Liang Bua must have looked like. If these videos of modern marabou storks and vultures are any indication, I?m not placing bets on who got the last scraps of Stegodon meat, but it may not have been a hobbit or even a komodo dragon:

The bird remains from Liang Bua paint a lively and colorful background for Homo floresiensis, but their implications extend far beyond a soundtrack to the hobbit story. Birds are closely associated to vegetation, and their presence throughout the stratigraphic sequence serves as a paleoecological signal, much more so than mammals. Changes in local climate affect vegetation, which in turn affects the bird community. The diverse assortment of birds in the Pleistocene sediments indicates that Liang Bua?s surroundings hosted a range of different habitats, including mature and floristically diverse forests that would have provided plenty of food and other resources for Homo floresiensis. In the Holocene sediments, bird diversity appears to drop. This may well be biased due to smaller sample sizes in the Holocene, but we cannot rule out changes in the local ecology. The absence of water birds (abundant in Pleistocene deposits) during the Holocene might reflect a shift to a drier climate, which is on par with isotope data from the region (Westaway et al., 2009).

Swiftlets over forest near Liang Bua

However, as the Wae Racang river changed its course, snipes and plovers may no longer have been attracted to the cave surroundings. Forest birds, such as swiftlets, parrots, and pigeons made it unscathed into the Holocene, indicating that despite a shift to a drier climate during the terminal Pleistocene, enough forest remained nearby to sustain populations of these birds. Interestingly, a majority of the bird species observed in the Pleistocene sediments are still found on the island today. While pygmy elephants, hobbits, giant marabou storks, and vultures disappeared toward the end of the Pleistocene, most birds seem unaffected by this extinction event, or were able to cope with changing environmental conditions. What made them different?

As more material is excavated and studied, the Liang Bua avifauna continues to grow and the resolution of its paleoecological and paleoenvironmental signal will increase. It might show us what happened to the wetlands and forests over time, tell us who was eating whom, and when each character arrived on the scene. Moreover, it allows us to test hypotheses about climate change, extinction patterns, and yes, human evolution.

I hear a clanking sound as the air condition comes back to life. Delicious cold air hits my face. Back to the birds it is.

References:

van den Bergh, G. D., H. J. M. Meijer, R. A. Due, K. Szabo ?? , L. W. van den Hoek Ostende, T. Sutikna, E. W. Saptomo, P. Piper, K. M. Dobney, and M. J. Morwood. 2009. The Liang Bua faunal remains: a 95 k.yr. sequence from Flores, East Indonesia. Journal of Human Evolution 57:527?537.

Meijer, H.J.M., Sutikna, T., Saptomo, W.E., Due, R. A., Wasisto, S., James, H.F., Morwood, M.J., & Tocheri, M.W. Late Pleistocene-Holocene non-Passerine Avifauna of Liang Bua (Flores, Indonesia). The Journal of Vertebrate Paleontology 33(4).

Morwood, M. J., P. Brown, Jatmiko, T. Sutikna, E. W. Saptomo, K. E. Westaway, R. A. Due, R. G. Roberts, T. Maeda, S. Wasisto, and T. Djubiantono. 2005. Further evidence for small- bodied hominins from the late Pleistocene of Flores, Indonesia. Nature 437:1012?1017.

Morwood, M. J., R. P. Soejono, R. G. Roberts, T. Sutikna, C. S. M. Turney, K. E. Westaway, W. J. Rink, J.-X. Zhao, G. D. van den- Bergh, R. A. Due, D. R. Hobbs, M. W. Moore, M. I. Bird, and L. K. Fifield. 2004. Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431:1087?1091.

Westaway, K. E., R. G. Roberts, T. Sutikna, M. J. Morwood, R. Drysdale, R., J.-X. Zhao, and A. R. Chivas. 2009a. The evolving landscape and climate of western Flores: an environmental context for the archae- ological site of Liang Bua. Journal of Human Evolution 57:450?464.

Images: by author.

Source: http://blogs.scientificamerican.com/guest-blog/2013/06/24/why-two-birds-in-the-hand-may-be-better-than-a-hobbit-skull-in-a-cave-deposit-at-least/

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