Nickel Creek, the self-described “progressive acoustic” band consisting of Chris Thile on mandolin and siblings Sara and Sean Watkins on fiddle and guitar, has been together (including breaks and hiatuses) for 34 years. Thirty-four years ago would be 1989, when the youngest member of the band, Sara Watkins, who is a year younger than me, would’ve been eight years old. It’s enough to make me self-conscious: when I was eight years old, I was just starting to read chapter books.

On Sunday night, Nickel Creek played to a packed audience at Wolf Trap, with Aoife O’Donovan — who has worked with Sara Watkins in the supergroup I’m With Her — opening the show.

With 34 years together as a band, Nickel Creek have an extensive catalog to draw from, but they recently released a new LP, Celebrants, and they opened at Wolf Trap on July 23 with a song from that album, “Where The Long Line Leads,” which features Sara on lead vocals. Chris introduced another song from the record, “Going Out,” by thanking the audience for coming out on a Sunday night; being in their 40s now, he said, they understood how hard it can be to come out. “Thinnest Wall,” as Sean explained, is a song about the middle of a relationship, rather than the beginning or the end. The set also included the title cut and “To The Airport,” which Chris introduced as a song about people you might see at the airport, unsurprisingly.

As a band based in bluegrass, instrumentals always make up a  part of Nickel Creek’s set. In addition to the aforementioned “Going Out,” they also played “The Elephant in the Corn.” Chris gave an extensive introduction to the old favorite, “To The Lighthouse.”  He apologized for getting political, but he brought up how the US government is decommissioning lighthouses, with the rationale that GPS has made them unnecessary. He expressed skepticism about the ability of GPS to prevent ships from hitting the rocks, but he was also enthusiastic about the prospect of the government auctioning off lighthouses to private owners. Chris seems like the kind of guy who’d make a good hermit living alone in a lighthouse, occasionally returning to society to play his music.

Sean wrote “21st of May.” The song was inspired by billboards he saw in Los Angeles, where he lives, that promised the world would end on May 21, 2011. As I’ve heard him quip before, when he appeared with Sara as the Watkins Family Hour at the Birchmere last year, he had the question of which time zone the proposed end of the world was synched with. Obviously, the world didn’t come to an end, and this preacher and his followers, who had lived as though it would — accumulating credit card debt in the anticipation they’d never have to pay it back — were left high and dry.

Watch Nickel Creek perform “21st of May” live for WNYC on YouTube:

The set included a number of audience favorites from the band’s extensive catalog: the title cut of the album This Side, “First and Last Waltz,” “Helena,” “Destination,” “Smoothie Song,” “Strangers,” “Sweet Afton,” “Someone More Like You,” and “I Should’ve Known Better.” They covered “Hayloft” by the band Mother Mother before closing the main set with “The Fox.” Eschewing the pageantry of leaving the stage and returning, after a momentary pause, they went into their encore, which consisted of “Scotch & Chocolate” and “Holding Pattern.”

In a classy move, Sean came out at the start of the evening to introduce the opening act, Aoife O’Donovan. Aoife performed in a trio with Isa Burke, who has also released records as a solo artists and with the band Lula Wiles, on electric guitar and backing vocals. The show started at 7:30, allowing O’Donovan to play a lengthy, hour-long set. Much of it was drawn from her latest LP, The Age of Apathy, which came out early last year. “Galahad”  references the Camelot knight who succeeded in the quest for the Holy Grail. “Phoenix” is inspired by the mythical bird that rose from the ashes. Introducing “Sister Starling,” Aoife told the audience, “I don’t actually know anything about birds,” and asked us to pretend the sparrows (someone in the audience told her what they were) were starlings; fittingly, a bird sang just before the band started playing.

Aoife’s set continued with “Prodigal Daughter.” Being on the road, she explained, “you get to a point where you can’t remember what happened where.” Sometimes, she said, you realize you’re in a place where a strange thing happened, which is what “Elevators” is about. She introduced “B61,” which is the name of a bus route to a seaside area of Brooklyn, as “a love song about public transportation.”

Watch Aoife O’Donovan perform “B61” live acoustically for the Age of Apathy Solo Sessions on YouTube:

Next up was “Hornets,” followed by “Porch Light,” from her 2016 album, In The Magic Hour; she called attention to the fact that it was the magic hour, and that we’re in the “porch season” now. Introducing the title cut of that album, she talked up an Irish children’s book she loves, called The Turf Cutter’s Donkey, about a magical donkey. (Of related interest: I learned yesterday you can rent a heard of goats to take care of overgrown, invasive vegetation. And now I’m wondering if I can rent a herd of goats just to hang out.)

Many years ago, Aoife covered, in its entirety, one of the albums that has most inspired her: Bruce Springsteen’s haunting, sparse Nebraska. Earlier this year, she toured playing the album for live audiences, appearing at the Birchmere in March. She gave the audience at Wolf Trap a “sample,” playing “Open All Night.” She closed the set with one of her older songs, “Red & White & Blue & Gold,” and one of her newest sons, “Passengers.”

One of the evening’s funnier moments came when Sara revealed that, for the first time in 20 years, she’d had a Coca-Cola, and was amped up from the caffeine. It’s a moment that captures the silliness and sense of whimsy that Nickel Creek always has even as they’re quite serious about their music and their playing. They’re always a lot of fun — as is Aoife — and the evening was a thoroughly entertaining experience.