Two Metro train stations were closed Sunday while hazardous materials crews investigated a number of dead birds and a substance at one that was identified as a commercial rat poison.

The Greenbelt station on the Green Line in suburban Maryland and the Takoma Park station on the Red Line in the city were closed, said Cathy Asato, a spokeswoman for Washington Metropolitan Area Transit Authority.

There were as many as 20 dead birds outside the Greenbelt station and one to three outside other stations, Asato said. The Anacostia and Naylor Road stations on the Green Line also were affected.

Investigators determined the substance at the Greenbelt station was d-Con rat poison, said District of Columbia Fire and EMS spokesman Alan Etter.

"We suspect very strongly that it's the same chemical at the other stations," Etter said.

He said investigators were looking for a person in a black pickup truck who witnesses saw spraying the material.

"Metro will have to figure out if this person works for them or is a contractor or what," Etter said.

No injuries were reported.