Sheep on the Orkney isles have been eating seaweed since animal husbandry was introduced in 3500 BC, new research suggests.
The landscape on the islands 5,500 years ago was predominantly treeless, as it remains today, so marine seaweed provided a useful alternative fodder.
The study found that sheep began to consume moderate amounts of seaweed from the moment of their introduction to Orkney.
This practice helped facilitate the successful spread of farming to one of the most remote areas of Europe.
Experts from the French National Centre for Scientific Research tested the remains of sheep on Skara Brae using isotope dating to make the finding.
This method measures the decay of isotopes – atoms of an element that have the same number of protons and electrons but different numbers of neutrons.
Scientists know how long these isotopes take to decay over time, so measuring their numbers provides a precise calculation of exactly how old a sample is.
They found, for the first time, that sheep did start eating seaweed as soon as they were brought to the islands.
However, it is not clear whether the sheep chose to consume the marine vegetation or if farmers directed them towards it.
Writing in the paper, its authors said: ‘It is not possible to establish whether Neolithic sheep turned to seaweed of their own accord or were brought to the shore by herders.
‘In any case, these results confirm the chronology of the gradual introduction of seaweed into the Neolithic sheep diet in Orkney, which may have been the result of changes in sheep behaviour or physiology.’
The study also found that, contrary to popular opinion, the introduction of seaweed to the diet of Orkney’s Neolithic sheep was not the start of an unbroken tradition.
Sheep during the Viking period on Orkney may have been separately imported, and stable isotope analyses indicate a year-round terrestrial diet for Viking-period sheep.
Furthermore, there is currently no evidence that Neolithic sheep ate seaweed outside of the winter months.
The modern sheep on North Ronaldsay show far higher levels of seaweed consumption, and other contemporary seaweed eating sheep are also known on Shetland and the Faroe Islands.
The practice may not have been continuous, but it is remarkable that sheep are still able to survive in such northern and exposed environments using the same strategies their Neolithic forbearers employed thousands of years ago.
The full findings of the study were published in the journal Antiquity.