Reserve Pits : Mortality Risks to Birds
A reserve pit is an earthen pit excavated adjacent to a drilling rig and is commonly used for the disposal of drilling muds and fluids in natural gas or oil fields. If the reserve pit contains oil or oil-based products (i.e. oil-based drilling fluids), the pit can entrap and kill migratory birds and other wildlife.
U.S. Fish and Wildlife Service
http://www.fws.gov/contaminants/Documents/ReservePitsBirdMortality.pdf, 2 MB
Mountain-Prairie Region Environmental Contaminants site