Donald Trump Jr. over the summer killed an endangered Mongolian Argali sheep, continuing the tradition he shares with his brother Eric of going to other countries and killing their rare wildlife, ProPublica reported Wednesday. 

Trump Jr., son of U.S. President Donald Trump, was days later retroactively given permission for killing the animal.

Bill McKibben, co-founder of climate advocacy group 350.org, tweeted that Trump Jr. was following his family's example.

"Further endangering endangered species seems to be the family hobby," McKibben said, a reference to how the president has systematically slashed species protections in the U.S.

According to ProPublica, the timing of the permit's issuance was a bit suspect:

The Mongolian government granted Trump Jr. a coveted and rare permit to slay the animal retroactively on Sept. 2, after he'd left the region following his trip. It's unusual for permits to be issued after a hunter’s stay. It was one of only three permits to be issued in that hunting region, local records show.

Afterward, Trump Jr. met privately with the country’s president, Khaltmaagiin Battulga, before departing the capital of Ulaanbaatar back to the U.S., according to Khuantai Khafezyn, a local government official in the region where Trump Jr. hunted the argali and a former government official with knowledge of the meeting. It isn’t clear what was discussed.

Animal rights activist Ari Solomon said on Twitter that Trump Jr.'s behavior was par for the course.

"While his father is trying to gut the Endangered Species Act, he's out killing endangered animals," said Solomon. "This family is trash."