After 25 days of darkness, workers and administrators at the Smithsonian museums and National Zoo lit up at the sight of visitors on their first day back Tuesday.

The director of the National Portrait Gallery stood at the door beckoning people inside.

“Welcome everyone, we’re open. Come in from the cold,” said an exuberant Kim Sajet. “We missed you guys.”

At the zoo, workers greeted early risers at the gates and offered updates on their favorite animals.

“Go on in,” Brandie Smith, the zoo’s associate director of animal care, said as she waved to a handful of frequent zoo-goers. “The animals — the primates especially — are going to be so happy to see you.”

Even the elephants wanted to say hello.

“They kept cutting up and looking at us, coming over to check us out,” said Stacy Tolar, 43, who was visiting the District from Louisiana. “I’ve never seen elephants react to people like that.”

But beneath the buoyant return to business as usual, Smithsonian administrators said there was still plenty to worry about: another looming deadline to fully fund the government by February and the impact of millions in lost revenue.

“It’s difficult,” said Steven Monfort, director of the zoo. “We have no control over these decisions being made. Mainly, I worry about our staff, who love what they do, and just wanted to get back to work.”

The partial government shutdown, which began Dec. 22, left nine federal departments and several agencies without funding — and hundreds of thousands of federal workers without pay.

As a debate over border security and funding for a wall on the U.S.-Mexico border stalled, the shutdown dragged on for 35 days to become the longest in U.S. history.

Kim Sajet, director of the National Portrait Gallery, left, and Stephanie Stebich, director of the American Art Museum, greet visitors and staff as the museums reopen Tuesday. (Jonathan Newton/The Washington Post)

Although Smithsonian museums and the zoo were able to hold off closing through the end of December by relying on reserve funds, Smithsonian Secretary David J. Skorton estimated that the shutdown cost the Smithsonian about $3.4 million in revenue, including lost food and beverage sales, Imax theater admissions and parking fees.

The National Portrait Gallery lost as many as 180,000 visitors, Sajet said, including 37 school groups that were forced to cancel their visits.

A family day set for Feb. 16 was canceled because contracts couldn’t get signed. Potential hires have been in limbo and the exhibition calendar is a mess, Sajet said. The June opening of “Marian Anderson: One Life” is in jeopardy.

The zoo, which receives 70 percent of its budget from the government and 30 percent from other sources of revenue, including visitors, is still calculating its losses.

“There’s a domino effect,” Sajet said. “We have to look at the entire schedule and see what we have to do, what we can postpone and what we will have to cancel so we can catch up.”

On the Mall, about 80 people were waiting in the cold outside the National Museum of African American History and Culture as it reopened at 10 a.m.

Visitors line up outside of the National Museum of African American History and Culture on Tuesday. (Bill O'Leary/The Washington Post)

Nick Lautman, an actor from London, was first in line — an hour before the museum opened — and intent on visiting the Smithsonian’s newest attraction. He arrived Jan. 22 for a vacation, celebrating his 27th birthday, that he had booked before the shutdown began.

He visited Mount Vernon, the Capitol, the U.S. Holocaust Memorial Museum (twice), the monuments, Ford’s Theatre and more while he hoped for the shutdown to end.

When he learned that the shutdown would come to a close, he extended his trip to Wednesday. He couldn’t go home without visiting the Smithsonian museums.

“From the British perspective, it seems mad to shut down the government,” he said.

Businesses offered free food and services to zoo employees who were required to work without pay throughout the shutdown, including more than 120 workers charged with caring for the animals.

Frequent visitors and volunteers dropped off snacks and hot beverages. Some, including those who work in the zoo’s commissary, worked alongside the unpaid staff.

The live animal cameras that stream the daily comings and goings of giant pandas and naked mole rats went dark. Businesses near the zoo reported a dip in foot traffic and a drop in revenue.

The museums, which had been shuttered since the beginning of the year, opened after lawmakers approved a bill that funded the government for three weeks.

When the zoo’s gates clattered open at 8 a.m., it was the usual group of locals and joggers who ambled in. They “oohed” and “ahed” as the pandas swung down tree branches and munched on bamboo. Several took photos and videos as the animals clambered around.

Although nearly 200 zoo employees worked without pay throughout the shutdown, Smith said, the animals seemed to miss their human visitors.

Steven Monfort, director of the National Zoo, smiles during the park’s reopening. (Astrid Riecken/For The Washington Post)

A fennec fox sleeps through the reopening of the National Zoo. (Astrid Riecken/For The Washington Post)

“You realize how much they appreciate having us there as entertainment,” Smith said. “We had zoo staff go by just to say hi so they would have some attention from people.”

Of course, the words “government shutdown” mean little to the apes and lions who live in the zoo. For the animals, life simply went on.

Several babies were born, including a kiwi chick, three otter pups and a kudu calf.

A baby golden lion tamarin was named Carolina after veterinarians confirmed it was a girl. The newly crowned naked mole rat queen appears to be pregnant again, keepers said, as four pups born last month continue to grow.

The naked mole rat babies, who were merely the size of jelly beans when the shutdown began, are now roughly as big as baby carrots.

“How dare they have babies when we were gone,” mused Merry Richon, a frequent visitor.

Even Redd, the 2-year-old Bornean orangutan infant, seems to have grown.

“I think he’s grown half a foot since we last saw him,” she told her husband, Allen Richon.

The couple, who visit the zoo five or six mornings a week, said they’ve missed all the animals — but especially the primates. As she spoke, Merry Richon showed off her shirt, which bore a close-up of Redd’s face.

“I call him my grandson,” she said. “I love him.”

The feeling, it seemed, is mutual.

As the Richons walked into the Think Tank, where Redd was playing with baskets and swinging from ropes, the baby ape sprang toward them, pressing his face up against the glass.

He pursed his lips and held up his arms.

“Oh, are you giving kisses?” Merry Richon said. “Yes, we missed you, too.”