Vikings in Madeira by Sarah Griffiths

It is popularly thought that Portuguese explorers colonized Madeira in the 15th century, but mouse bones suggest that the Vikings visited the island four centuries beforehand. Scientists also believe that the mouse population that stowed away on their boats led to an ‘ecological disaster’ and the extinction of native birds. House mice reached the island in the year 1036 - four centuries before the Portuguese colonisation - according to a study published in the journal proceedings of the Royal Society B. The discovery comes after experts dated old mouse bones found at Ponta de São Lourenço, to the east of the island. Researchers from the Mediterranean Institute for Advanced Studies (Imedea) in Majorca and the University of La Laguna, Tenerife, analysed two samples of bones and while the first yielded no information, the second was dated to between 900 and 1030AD, which is the earliest evidence of the presence of mice on the island.

‘Current populations of house mice on Madeira show similarities in mitochondrial DNA with those in Scandinavia and northern Germany, but not with those in Portugal,’ said Josep Antoni Alcover of Imedea. This hints that the mice were neither indigenous nor hitched a ride on the ships of Portuguese settlers who took possession of the island in 1419.

‘The second sample analysed leads us to think that the Vikings…[carried] the mice.’

He explained that more morphological and genetic studies of the remains are needed and there are no historical references of Vikings travelling to the island. However, if the findings are correct and Vikings did land on Madeira long ago, they may have triggered significant ecological changes on the island.

The researchers believe that the first human visitors began the extinction of endemic bird species on the island. They think the mice quickly thrived due to their reproductive potential and the lack of rats – and their predatory activity wiped out eggs and chicks of small and medium birds such as the quail and rail.

The researchers said that atleast two thirds of the endemic birds and two non-endemic species became extinct, which in turn enabled predators such as owls to prosper.

‘The introduction of the mice probably resulted in an ecological disaster, based on the extinction of endemic birds and changing the ecology of the island four years earlier than previously thought,’ Mr Alcover said.