The End of the Megafauna on Madagascar

Nearly all of Madagascan megafauna - including the famous Dodo, gorilla-sized lemurs, giant tortoises, and the Elephant Bird which stood three meters tall and weighted close to a half ton - vanished between 1500 and 500 years ago. Why?

The Mascarene islands are situated east of Madagascar and are interesting because they are among the last islands on earth to be colonized by humans. Intriguingly, the islands' megafauna crashed in just a couple of centuries following human activity. In a recent study, a team of researchers found that it was likely a combination of heightened human activities in combination with a particularly severe spell of region-wide aridity that may have doomed the megafauna[1].

[By analyzing stalagmites from the La Vierge Cave located on Rodrigues the
scientists reconstructed 8000 years of the region's past climate]
[Image: Hanying Li]

The primary source of this new paleoclimate record came from the tiny and remote island of Rodrigues in the southwest Indian Ocean approximately 1600 km east of Madagascar. Li and colleagues built their climate records by analyzing the trace elements and carbon and oxygen isotopes from each incremental growth layer of stalagmites which they collected from one of the many caves from this island. Variations in the geochemical signatures provided the information needed to reconstruct the region's rainfall patterns over the last 8000 years.

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.

Research shows that the hydroclimate of the region experienced a series of drying trends throughout the last eight millennia, which were frequently punctuated by 'megadroughts' that lasted for decades. The most recent of the drying trends in the region commenced around 1500 years ago at a time when the archaeological and proxy records began to show definitive signs of increased human presence on the island.

While the scientists cannot say with 100 percent certainty whether human activity, such as overhunting or habitat destruction, was the proverbial last straw, the paleoclimate records make a strong case that the megafauna had survived through all the previous episodes of even greater aridity. This resilience to past climate swings suggests that an additional stressor contributed to the elimination of the region's megafauna.

The study sheds new light on the decimation of flora and fauna of 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 from Mauritius and the saddle-backed 'Rodrigues giant tortoise' endemic to Rodrigues.

The story our data tells is one of resilience and adaptability of the islands' ecosystems and fauna in enduring past episodes of severe climate swings for eons - until they were hit by human activities and climate change, the researchers conclude.

[1] Li et al: A multimillennial climatic context for the megafaunal extinctions in Madagascar and Mascarene Islands in ScienceAdvances - 2020