ISLA DE ASIA, Peru  The worldwide boom in commodities has come to this: Even guano, the bird dung that was the focus of an imperialist scramble on the high seas in the 19th century, is in strong demand once again.

Surging prices for synthetic fertilizers and organic foods are shifting attention to guano, an organic fertilizer once found in abundance on this island and more than 20 others off the coast of Peru, where an exceptionally dry climate preserves the droppings of seabirds like the guanay cormorant and the Peruvian booby.

On the same islands where thousands of convicts, army deserters and Chinese indentured servants died collecting guano a century and a half ago, teams of Quechua-speaking laborers from the highlands now scrape the dung off the hard soil and place it on barges destined for the mainland.

“We are recovering some of the last guano remaining in Peru,” said Victor Ropón, 66, a supervisor from Ancash Province whose leathery skin reflects his years working on the guano islands since he was 17.