A comprehensive study using records spanning 1,500 years shows how white-tailed and golden eagles were once found across Britain and Ireland, but populations plummeted as a result of human activity.

A research team from RSPB Scotland mapped the population of both eagles between 500 AD and the present day, by using historical records, scientific knowledge of the birds' ecology and even by looking for places with names that suggested they once were home to eagles.

That includes towns like Aron Crag in Cumbria, which means "Eagle Cliff" in Old English; Arndale Hole in North Yorkshire, which means "Eagle Valley" in Norse; and Knockananiller in Dublin, which is "Eagle Hill" in Irish Gaelic.

The results showed a steep decline, with golden eagle numbers dropping by two-thirds from 1000-1500 breeding pairs in 500AD to just 300-500 in 1800. White-tailed eagles were hit even harder, as 80 to 90 percent of the population was lost over the same period.

The white-tailed eagle was eventually driven to extinction in Britain in the early years of the 1900s, thanks to continued killing by humans. Golden eagles almost exclusively live in Scotland, now, with about 440 breeding pairs presently alive.

"The results of this study are striking as they provide compelling evidence that eagles were widespread throughout most of Britain and Ireland in the Dark Ages," said RSPB Scotland's Richard Evans, lead author of the study.

"Between 500 and 1800 we see massive loss of eagle range in the south, which is consistent with the effects of habitat loss and killing by humans."

The white-tailed eagle was reintroduced to the Isle of Rum, in the Small Isles archipelago in Scotland, in 1975. It now breeds throughout the Western Isles and the mainland coast of Wester Ross, but its population is a shadow of what it was in the Dark Ages.