Here the island dips into a broad, shallow depression where guano was once mined.
Johnston Island was annexed into the United States as a guano island under the Guano Act of 1856.
They roost on an offshore platform erected to collect guano (bird droppings).
Millennia of visiting seabirds left large fossilized guano deposits on Nauru.
Between 1848-1875 20 million tons of guano was exported from Peru to North America and Europe.
Their droppings over the centuries have coated offshore islands with guano hundreds of feet think.
We sat for ages, just gazing at the Bass Rock, its thick covering of guano making it glisten like a wedding cake in the sun.
Those islanders were forced to work under horrific conditions in the guano mines of Peru.
The copious guano deposition from sea birds may play a role in maintaining the present assemblage of vascular plants on both islands.
He has drawn particular attention to the amount of organic waste once generated by the seabird colonies - mainly guano , but also lost eggs, dead birds, spilled food, and molted feathers.