The guano (seabird poop) trade was a really big deal in the 19th century, Spain even tried to steal some islands from Peru because they had significant guano deposits (http://www.environmentandsociety.org/tools/keywords/guano-wa...).

Eventually guano became less valuable since artificial fertiliser was cheaper. I don't think there's any significant guano trade now, and definitely not in the range of $1B / year. The article seems to be suggesting that the indirect benefits of guano (birds dropping it over fields) is worth $1B / year. Somewhat misleading title IMO.