Giant animals vanished from Madagascar after humans arrived
About 500 to 1,500 years ago, Madagascar lost nearly all of its megafauna, including giant tortoises, Dodo birds, lemurs the size of gorillas, and 10-foot-tall elephant birds that weighed half a ton. While the exact cause of these extinctions remains a mystery, a new study from the University of Innsbruck reports that human activities likely compounded the impacts of climate change when Madagascar’s giant animals simultaneously disappeared.
Previous theories suggest that populations of the oversized wildlife collapsed under the strain of overhunting by humans or crashed when the climate abruptly changed.
The Mascarene islands east of Madagascar are of particular interest to scientists because they are among the last islands on earth to be colonized by humans. The islands’ megafauna crashed in just a couple of centuries following human settlement.
In the current study, the international team of experts led by Innsbruck determined that the extinction event was caused by a “double whammy” of heightened human activities combined with an intense period of dry spells and megadroughts. The researchers ruled out climate change as being the sole cause of the collapse of the giant creatures, and found that the impact of human colonization was a crucial contributor.
Study lead author Hanying Li of Xi’an Jiaotong University and colleagues reconstructed a detailed record of the region’s climate fluctuations. The new paleoclimate record was preserved in stalagmites that were collected from a cave on the tiny Mascarene island of Rodrigues – approximately 1,600 kilometers east of Madagascar. According to Professor Gayatri Kathayat, the island of Rodrigues is so remote and small that it cannot be found on most schoolbook atlases.
“Variations in the geochemical signatures provided the information needed to reconstruct the region’s rainfall patterns over the last 8,000 years. To analyze the stalagmites we used the stable isotope method in our lab at Innsbruck,” explained Professor Christoph Spötl.
Study senior author Hai Cheng noted that despite the distance between the two islands, the summer rainfall at Rodrigues and Madagascar is influenced by the same global-wide tropical rain belt that oscillates north and south with the seasons. “And when this belt falters and stays further north of Rodrigues, droughts can strike the whole region from Madagascar to Rodrigues,” said Cheng.
The study revealed that the region experienced a series of drying trends throughout the last 8,000 years, which were characterized by frequent megadroughts that lasted for decades. The most recent of these extreme spells struck the islands about 1,500 years ago, just as human presence increased throughout the region.
The research sheds new light on the decimation of wildlife on Mauritius and Rodrigues. “Both islands were rapidly stripped of endemic species of vertebrates within two centuries of the initial human colonization, including the well-known flightless ‘Dodo’ bird from Mauritius and the saddle-backed ‘Rodrigues giant tortoise’ endemic to Rodrigues,” explained study co-author Aurele Anquetil André.
“While we cannot say with 100 percent certainty whether human activity, such as overhunting or habitat destruction, was the proverbial last straw that broke the camel’s back, our paleoclimate records make a strong case that the megafauna had survived through all the previous episodes of even greater aridity,” said study co-author Ashish Sinha. “This resilience to past climate swings suggests that an additional stressor contributed to the elimination of the region’s megafauna.”
The study is published in the journal Science Advances.