To most people, bird poop is just something they scrape off the windshield of their cars, but it's more important than we may think. In fact, droppings were once a very important commodity in the United States. Buying and selling bird poop is not as featherbrained as it may seem either. This stinky substance, referred to as bird guano, was sailed around the world during the 19th century to be sold as the principal agricultural fertilizer in the United States.

Six tourists were arrested at the Machu Picchu on suspicion of defecating among the ruins and destroying stonework at the 15th-century citadel, Reuters reported Tuesday , citing Peruvian authorities. The unnamed tourists, who were four men and two women, had come from Argentina, Brazil, Chile, and France, CNN reported , citing authorities at the ancient site. They were all 20 to 32 years old, CNN reported. It's not clear whether they traveled to the site together or met there. They had entered an area within the sacred Temple of the Sun , a semicircular structure built by the Incas to worship their sun god, CNN reported. Reuters cited local authorities as saying that the tourists caused a rock to fall from a wall of the temple and that at least one of them defecated inside the citadel. Five of the tourists are facing deportation from Peru, but the sixth, an Argentine man said to have acknowledged a leading role in the vandalism, is to remain in the country to be charged with "destroying Peru's cultural heritage," according to Reuters.

The three main macronutrients in any fertilizer are nitrogen, phosphorus, and potassium. At the time Mount Tambora erupted, nitrogen sources included blood, fish, and manure; phosphorus from rock phosphate, bones, fish, and seaweed; potassium from greensand, kelp, and ash. Agricultural science promoted these fertilizers still popular today, and I have sacks of most of them , but the favorite product was South American guano. Peruvian guano has been used as a fertilizer for centuries.

The Peruvian government is stepping up its security at Machu Picchu after some tourists pooped on the ancient site. Six tourists were arrested after human feces were found in a sacred room in the ancient site. Now, Peru is turning to technology to make sure they can preserve the site form further defacement. Five tourists were deported to Bolivia after the feces was discovered in the Temple of the Sun.