Guano is the name given to seabird excrement and a very effective natural fertilizer due to its exceptionally high content of nitrogen, phosphate and potassium. It was Peru's main export in the mid 19th century, when huge amounts were harvested for export to the USA and Europe. Chinese workers began to arrive in Peru in 1849; they often lived temporarily at the extraction sites in caves such as these in this image, very harsh conditions indeed in the fierce desert heat....