How Amsterdam Island Turned into an Unlikely Haven For Feral Cows
In 1871, a farmer dumped five cattle on a small, inhospitable island in the middle of the southern Indian Ocean. Against all odds, this tiny herd not only survived but also flourished, adapting to its harsh new home and multiplying, reaching a population of around 2,000 individuals by the late 1980s.
By all accounts, this should not have happened. The founding group was too small and the genetic diversity too low to sustain a viable population for any length of time. So, why was this particular band of bovines so successful? According to recent research, it may have come down to a fortuitous combination of genetics and climate.
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A Short History Of Amsterdam Island’s Feral Cows
In 2010, conservationists made the hard and controversial decision to cull hundreds of feral cattle that had improbably colonized Amsterdam Island, a 21-square-mile (55-square-kilometer) volcanic dome. Though there are no permanent human settlements on the island, it is home to a number of plant and animal species, including the endemic (and endangered) Amsterdam albatross, and the unruly herd was becoming a bit of a problem.
The cows had secured a foothold in the remote subantarctic island over a hundred years earlier, after being abandoned by a French farmer from Réunion. This was despite the isle’s challenging conditions, including a persistently cool, damp climate, limited resources, and relentless winds, along with the original herd’s small size and low genetic pool.
Aside from a short-lived population collapse caused by disease, the number of cattle on the island rapidly multiplied, reaching approximately 2,000 individuals in the 1950s and 1980s.
The Key to Amsterdam Island Cow Survival
It’s not uncommon for an invasive species to thrive after finding land free from natural predators and competitors. But it helps to have a large founding population with a high level of genetic diversity, and this is what makes the Amsterdam Island cattle unusual. According to the archives, the original population consisted of just five cattle — a fact supported by recent research published in Molecular Biology and Evolution.
The study’s authors reached this conclusion after analyzing historical DNA samples from 18 Amsterdam Island cows. The analysis suggested a sharp decline in population size approximately 22 generations earlier, coinciding with their reported abandonment on Amsterdam Island in 1871.
By comparing these samples with global cattle populations, the team also determined the cattle’s genetic origin. Here lay the key to their survival.
Around a quarter of their ancestry belonged to the Indian Ocean Zebu. The remaining 75 percent belonged to European taurine cattle, related to today’s Jersey breed. Crucially, conditions on Jersey are not too dissimilar to those of Amsterdam Island.
“Our genomic results suggest that mutations already present in the genome of these founding animals played a role in the Amsterdam Island cattle population’s rapid adaptation to life in the wild within a few generations,” Laurence Flori, a scientist from France’s National Research Institute for Agriculture, Food and Environment, who was involved in the study, told Discover.
Adapting to Life on Amsterdam Island
Observers noted that the Amsterdam cows soon became feral and behaved more fiercely than domestic cattle.
Records suggest herds on the island adopted complex social hierarchies commonly seen in wild bovids. This includes groups comprising females and young males, and separate groups comprising adult males, with mixed groups taking place at the start of the reproductive season.
It’s also been suggested that isolation may have led to the cattle’s shrinking, though the Molecular Biology and Evolution disputes this. Dwarfism, whereby large animals become smaller than their mainland counterparts, usually occurs over thousands of years.
The authors of a 2017 Scientific Report paper say the Amsterdam Island cattle shrank to around three-quarters of their body size. However, other researchers argue that the cattle’s small size stems from the modest stature of the original breeds.
Regardless, examples of feralization in cattle are extremely rare, which is why the Amsterdam cows “represented a very interesting genetic resource for studying this complex process,” said Flori to Discover.
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