Interior Secretary Ryan Zinke arrived on horseback for his first day of work Thursday.

The morning after his swearing-in ceremony, the former Montana congressman and Navy SEAL joined the U.S. Park Police at their stables on the National Mall.

He rode a 17-year-old Irish sport horse named Tonto through downtown Washington to the Interior Department's headquarters. Nine park police also on horseback accompanied him.

'Secretary Zinke was proud to accept an invitation by the U.S. Park Police to stand shoulder to shoulder with their officers on his first day at Interior,' said Interior spokeswoman Heather Swift.

Interior Secretary Ryan Zinke arriving for his first day of work at the Interior Department in Washington aboard Tonto, an 17-year-old Irish sport horse

New Interior Secretary Ryan Zinke greets employees after riding in on horseback with a U.S. Park Police horse mounted unit to report for his first day of work

Secretary Zinke (2nd from right) rode on horseback with a U.S. Park Police horse mounted unit

Secretary Zinke tipped his cowboy hat after riding in on horseback

Zinke and Interior Twitter accounts posted photos that showed him in a black cowboy hat astride a brown bay roan gelding that stands just over 17 hands tall, a bus and typical morning traffic in the background.

At the department, hundreds of federal workers greeted Zinke, including an Office of Indian Affairs employee from the Northern Cheyenne tribe from Montana who played an honor song on a hand drum.

While Zinke's urban horse ride is unlikely to become a daily ritual, he seems committed to preserving his image as an avid outdoorsman.

He wears a bright orange ballcap and hunting vest in the bio photo of his new @secretaryzinke Twitter account. And he has already retweeted a photo showing him and his wife at Glacier National Park in Montana.

The Interior Department oversees 400 million acres of public land, mostly in the West.

Secretary Zinke is preserving his image as an avid outdoorsman. He has already retweeted a photo showing him and his wife at Glacier National Park in Montana

Vice President Mike Pence, right, shakes hands after administering the oath of office to Interior Secretary Ryan Zinke, left, in the Eisenhower Executive Office Building

Vice President Mike Pence applauds as newly sworn in Interior Secretary Ryan Zinke, right, speak in the White House complex in Washington

On his first full day in office, Zinke issued an order Thursday reversing a last-minute action by the Obama administration to ban lead ammunition and fish tackle used on national wildlife refuges.

Gun-rights supporters condemned the earlier order - issued a day before Obama left office January 20 - as nakedly political. The order was intended to protect birds from lead poisoning, the Obama administration said.

Zinke, a former Montana congressman and avid hunter, said the new order would increase hunting, fishing and recreation opportunities on lands managed by Fish and Wildlife Service.

The order reverses a decision by the Obama administration to phase out use of lead ammunition and fishing tackle on wildlife refuges by 2022.

Zinke said the hunting order and another order directing agencies to identify areas where recreation and fishing can be expanded were intended to boost outdoor recreation in all its forms.

On his first full day in office, Zinke issued an order Thursday reversing a last-minute action by the Obama administration to ban lead ammunition and fish tackle

Interior Secretary Ryan Zinke, left, kisses his wife Lolita Hand after Vice President Mike Pence, right, administers the oath of office

'Outdoor recreation is about both our heritage and our economy,' he said in a statement. 'Between hunting, fishing, motorized recreation, camping and more, the industry generates thousands of jobs and billions of dollars in economic activity.'

Environmental groups slammed the new directive on lead ammunition, arguing that spent lead casings cause poisoning in 130 species of birds and other animals.

Switching to nontoxic ammunition should be 'a no-brainer' to save the lives of thousands of birds and other wildlife and to 'prevent hunters and their families from being exposed to toxic lead and protect our water,' said Jonathan Evans, environmental health legal director at the Arizona-based Center for Biological Diversity.

Evans called it ironic that one of the first actions by Zinke - a self-described champion of hunters and anglers - 'leads to poisoning of game and waterfowl eaten by those same hunting families.'