The edges of Adult Top 40 always shift, but never as much as in the last 18 months. A format once defined by not playing anything that could be construed as Hip-Hop is now the format where some stations feature the Black Eyed Peas in their music-image promos. Ke$ha has become a mom’s running-buddy, not a bad influence on her own kids. And last week’s rebranding of KZZO (The Zone) Sacramento, Calif., as Now 100.5 was a different animal—not a heritage Hot AC evolving with the landscape, but a new station with Top 40-style rotations and imaging.

We asked Adult Top 40 PDs about the records that defined the shifting boundaries of their radio station—the songs they never thought they’d play (but are), the songs they’re still not sure about, the most traditionally AC songs that define their softer edge, and the Hot AC warhorses that have finally been pulled from the library, no matter how well they test.

We expected, and got, a wide range of answers. There are as many different evolutions in the Adult Top 40 format as there are radio stations. Rhythm is the challenge for most, but not all; some Rock titles are pushing the boundaries as well, even in a format that crossed the Linkin Park threshold many years ago.

Here’s the full list of PD responses:

The song on my station that I never would have thought Adult Top 40 would play a year ago is:

Tony Mascaro, PD, WPLJ New York: Taio Cruz, “Break Your Heart” – “And I’ve been on it about [three months].”

Mark Adams, PD, KHMX (Mix 96.5) Houston: Taio Cruz, “Break Your Heart”

Leighton Peck, PD, KSTP-FM (KS95) Minneapolis: Jason Derulo, “In My Head”

Kent Phillips, PD, KPLZ (Star 101.5) Seattle: Ke$ha, “Tik Tok”

Ron Price, PD, KMXP (Mix 96.9) Phoenix: Muse, “Uprising”

Dave McKay, PD, WPST Trenton, N.J./Philadelphia: B.O.B., “Nothin’ On You” – “I would have never guessed it would be on our station outside nights.”

Bob Neumann: PD WRMF West Palm Beach, Fla.: Taio Cruz, “Break Your Heart”

Nevin Dane: OM/PD KQKQ (Q98.5) Omaha, Neb.: Muse, “Uprising”

Scott Sands, OM WZPL Indianapolis: “Ke$ha, B.O.B., Taio Cruz, and Muse all come to mind for some Adult Top 40 stations, but they have always had a place on WZPL. We even played Theory of a Deadman, ‘Bad Girlfriend’ – a lot!”

Charese Frugé, PD KSCF (Sophie 103.7) San Diego/KMXB (Mix 94.1) Las Vegas: Jason Derulo, “In My Head”

Doug Hamand, OM WMTX (Mix 100.7) Tampa, Fla.: Theory Of A Deadman, “Not Meant To Be”

Chad Rufer, PD WINK Fort Myers, Fla., Jason Derulo, “In My Head”

Brian Demay, PD WTSS (Star 102.5) Buffalo, N.Y.: Jason Derulo, “In My Head”

Dana Jang, PD KEZR (Mix 106.5) San Jose, Calif.: Muse, “Uprising”

Randy Cain, PD KURB (B98.5) Little Rock, Ark.: Anything by Lady Gaga

Jon Daniels, PD WMJC Long Island, N.Y.: Jason DeRulo, “In My Head”

Keith Kennedy, PD WKDD Akron, Ohio: B.O.B., “Nothin’ On You” – “It really is a great pop song.”

Brian Kelly, PD WMYX (Mix 99) Milwaukee: Lady Gaga, “Poker Face”

Dylan Sprague, PD, KALC (Alice 105.9) Denver: Ke$ha, “Tik Tok” – “But not because it’s rhythmic [but because of the sound of the song. The verses are delivered in a somewhat juvenile manner and the lyrics follow suit. Typically, this is the line adults won’t cross. It’s clear that pop culture is at the peak of the pop movement—massive resistance to this sound can’t be far away.”

The big CHR hit that I’m still not sure is right for this radio station is:

Mascaro: B.O.B., “Nothin’ On You” – “Just because there’s a little bit of rap element. And it hasn’t tested as well in callout as some of the others have—even with all the play B.O.B. got in the market.

Adams: B.O.B., “Nothin’ On You”

Peck: B.O.B., “Nothin’ On You” – “Good hook, but violates the ‘no rap’ code Hot AC lives by. At least here.”

Phillips: Ke$ha, “Tik Tok”

Price: Ke$ha, “Tik Tok”

McKay: Usher, “OMG” – “I’m not sure why, but this one doesn’t feel like a song that will cross over. Black Eyed Peas’ ‘Imma Be’ was the same. It just feels like it would never get out of nights.”

Neumann: “I’m pretty clear on what I think is right or wrong, so I couldn’t say ‘I’m not sure’ on any song.”

Dane: B.O.B. f/Hayley Williams, “Airplanes”

Sands: “Usher and Jay-Z type hits.”

Frugé: B.O.B. f/Hayley Williams, “Airplanes”

Hamand: Usher, “OMG”

Rufer: B.O.B., “Nothin’ On You”

Demay: Lady Gaga, “Alejandro”

Jang: Usher, “OMG”

Cain: Ke$ha, “Tik Tok”

Daniels: B.O.B. f/Hayley Williams, “Airplanes” – “We’ve been playing ‘Nothin’ On You,’ but despite being a great song, this seems to be more rap-based than the first single.” That said, Daniels wrote back several days later to say that WMJC was now playing “Airplanes” because of its callout scores.

Kennedy: Usher, “OMG”

Kelly: Rihanna, “Rude Boy”

Sprague: “We never played ‘Party In The USA,’ ‘Paparazzi,’ ‘Carry Out,’ or ‘Down,’ although many other Hot ACs did. We are very cautious with this product though. Each song is evaluated on its overall acceptance in Denver – not on the Hot AC panel.”

The recent song that we play that differentiates us from a Mainstream Top 40 is:

Mascaro: Nickelback, “This Afternoon”

Adams: Rob Thomas, “Mockingbird”

Phillips: “Rascal Flatts, Keith Urban, Lady Antebellum – Country hits.”

Price: Pearl Jam, “Just Breathe”

McKay: Rob Thomas, “Mockingbird,” Colbie Caillat’s “Never Told You” – “And, to a lesser extent, John Mayer’s ‘Half Of My Heart,’ but I could definitely see that one crossing over.”

Neumann: “Alex, I’ll take ‘anything with a guitar in it’ for 100.”

Dane: Phoenix, “1901”, 30 Seconds to Mars, “Kings & Queens,” Muse, “Uprising”

Sands: Michael Buble – “Maybe.”

Frugé: Jack Johnson, “You And Your Heart”

Hamand: Michael Bublé, “Haven’t Met You Yet”

Rufer: Nickelback, “This Afternoon”

Demay: Goo Goo Dolls, “Home”

Jang: The Fray, “Syndicate”

Cain: “It was Michael Bublé [which Top 40 is now playing].”

Daniels: “Choose from John Mayer, Rob Thomas, Sara Barielles, or Muse.”

Kennedy: Train, “If It’s Love” – “At least for now. It was nice to see ‘Hey Soul Sister’ go from us to them this time.”

Kelly: John Mayer, “Half Of My Heart”

Sprague: Rob Thomas, “Someday.”

The best song on the station right now is:

Mascaro: Sara Bareilles, “King Of Anything” – “A monster for us already.”

Adams: Pink, “Glitter In The Air”

Peck: “There are several great songs for us right now, but I’d have to say Katy Perry, ‘California Gurls.’”

Phillips: Train, “Hey Soul Sister” – “Pat [Monahan] lives in Seattle. We added it first in the country and the song lives on in multiple formats with surprisingly little burn.”

Price: Pearl Jam, “Just Breathe” – “A tie with The Script.”

McKay: “This is a tough one, because there are a few. I could say Kris Allen, Adam Lambert, or Lady Antebellum, but I’ll go with Lady Gaga’s ‘Telephone.’”

Neumann: Katy Perry, “California Gurls”

Dane: Mike Posner, “Cooler Than Me”

Sands: Katy Perry, “California Gurls”

Frugé: Katy Perry, “California Gurls”

Hamand: Train, “Hey Soul Sister”

Rufer: Katy Perry, “California Gurls”

Demay: Train, “Hey Soul Sister” – “A year going, still no burn, still getting requests.”

Jang: Lady Gaga, “Telephone”

Cain: Sara Bareilles, “King Of Anything”

Daniels: “It’s hard to choose just one. It’s probably between Train, ‘Hey Soul Sister’ and Katy Perry, ‘California Gurls.’ Both songs have a great summer feel.”

Kennedy: “Tie: Ke$ha, ‘Your Love Is My Drug’ and Katy Perry, ‘California Gurls.’ It’s impossible to not sing along when these spin.”

Kelly: Train, “Hey Soul Sister”

Sprague: “The big three are ‘Need You Now,’ ‘I Gotta Feeling,’ and ‘Hey Soul Sister’—talk about not going away.”

The song that represents the “AC” edge of the station now is:

Mascaro: Michael Bublé, “Haven’t Met You Yet”

Adams: Colbie Caillat, “Bubbly”

Peck: Keith Urban, “You’ll Think Of Me”

Phillips: Michael Bublé, “Haven’t Met You Yet” – “Smash for us in callout for six months.”

Price: Shawn Colvin, “Sunny Came Home”

McKay: Sheryl Crow, “Strong Enough” – “Or maybe one of the Goo Goo Dolls ballads.”

Neumann: Sheryl Crow, “All I Wanna Do”

Sands: Michael Bublé, “Haven’t Met You Yet”

Frugé: Colbie Caillat, “I Never Told You”

Hamand: Lifehouse, “Halfway Gone”

Rufer: Lisa Loeb, “Stay (I Missed You)” or Paula Cole, “I Don’t Want To Wait”

Demay: Colbie Caillat, “I Never Told You” (current) and Sarah McLachlan, “I Will Remember You” (gold)

Jang: Mariah Carey, “We Belong Together”

Cain: Celine Dion, “Because You Love Me”

Kennedy: John Mayer, “Half Of My Heart”

Kelly: Faith Hill, “Breathe”

Sprague: Uncle Kracker, “Drift Away” or Aerosmith, “I Don’t Wanna Miss A Thing”

The song that I finally took out of the library (even if it still tests) is:

Mascaro: “I can’t come up with just one song but it was the softer Bryan Adams songs or even the Shanias. They sounded a little too old and farty.”

Adams: Bon Jovi, “Livin’ On A Prayer”

Peck: Bryan Adams, “Summer Of ‘69” – “Finally!”

Phillips: Sheriff, “When I’m With You” – “It was just time. We played it [before it was released in America] in 1982 and then again as a hit in [1989]. God, I’m old!”

McKay: Bon Jovi, “Livin’ On A Prayer” – “It was really tough, being that we’re in New Jersey, but the song is almost 25 years old.”

Neumann: Norah Jones, “Come Away With Me”

Dane: Sheryl Crow “Soak Up The Sun,” Ben Folds Five “Brick,” Smashing Pumpkins “1979”, etc.—“Lots of ’90s/millennial titles that [started] to sound dated. With the onslaught of Gaga, Kesha, Jason Derulo, etc.”

Frugé: Beyoncé, “Single Ladies (Put A Ring On It)”

Hamand: Dionne Farris, “I Know”

Rufer: Chumbawamba, “Tubthumping”

Demay: Rod Stewart, “Have I Told You Lately”—“Yuck!”

Jang: Fleetwood Mac, “Landslide [1997 Version]”

Cain: “We’re taking a break from some ’80s R&B—Cameo, Dazz Band, Gap Band—that Little Rock never seemed to lose passion for.”

Daniels: Bon Jovi, “Livin’ On A Prayer”

Kennedy: Def Leppard, “Pour Some Sugar On Me” – “It will test until the end of time.”

Kelly: Ryan Cabrera, “True”

Sprague: Sixpence None The Richer, “Kiss Me”