After talking about 99 balloons...

Always like Nancy Sinatra - Boots song - Full metal jacket
https://www.youtube.com/watch?v=pV-iL-1mjf8

I think the bass line was written or simply improvised and recorded by studio bassist Carol Kaye.
She probably was in the studio every working day for a couple of decades.

I never heard of Carol Kaye, that's interesting. Looks like she had a huge influence over many bands. A female bass guitarist in the 50s. Looks like she impacted so many bands. Thanks for sharing.

Same here, never heard of her but always thought the bass line on "Boots" was great. Thanks for the knowledge, I enjoyed doing some reading about her.

Could start a Carol Kaye thread, but that would be a winter project.
And it was the 60's and 70's, here's just a snip from an interview:
"some funky things with Peggy Lee, but my favorite recordings are: "The Way We Were" (Barbra Streisand), "Feelin' Alright" Joe Cocker, "Feel So Bad" Ray Charles, "Wichita Lineman" Glen Campbell, "Good Vibrations" "Help Me Rhonda", "Heroes & Villains," and Pet Sounds with Brian Wilson (Beach Boys)"

"Wichita Lineman" has been my earworm for months now, need a new worm.
She created the bass introduction and the fast riffs between the verses, but I'm pretty sure Glen played the lead solo on a Fender Bass 6.

From the Website Carol Kaye Bass Hits,
https://www.carolkaye.com/www/library/basshits.htm

Yes, she did play bass on some of the Paul Revere hits. I wouldn't be surprised if that includes "Hungry" which has 3 overlapping bass tracks.
Could be the new earworm? Or one from this partial list of hits:

Whipped Cream - Herb Alpert, Spanish Eyes - Al Martino,
Good Vibrations, Help Me Rhonda, Sloop John B, I Get Around, Wouldn't It Be Nice (dano), Calif. Girls, God Only Knows, Pet Sounds lp, Heroes & Villains, Caroline No, Surf's Up, Child Is The Father Of The Man, Do You Like Worms?, Smile lp, Cabinessence, Fire sessions, I Was Made To Love Her, Let Him Run Wild - Beach Boys
Little Green Apples, Hickory Holler - O.C. Smith
Goin' Out Of My Head/Can't Take my Eyes Off Of You medley, Hurt So Bad, Shangrila, When I Fall in Love, More, Theme from Summer Place, etc. - Lettermen
Something Stupid - Frank & Nancy Sinatra
Boots, Sugar Town, You Only Live Twice theme, etc. - Nancy Sinatra
Feelin' Alright - Joe Cocker
The Way We Were - Barbra Streisand
Tell Her You Love Her, The World We Knew (OD dano fuzz on "World"), How Do You Keep The Music Playing, etc. - Frank Sinatra
Hold Me Thrill Me etc. - Mel Carter
Godfather Theme, Love Story, Can't Take My Eyes Off Of You, etc. - Andy Williams
In The Heat Of The Night, I Don't Need No Doctor, America The Beautiful, Eleanor Rigby, I Chose To Sing The Blues, Here We Go Again, Don't Change On Me,
Feel So Bad, Understanding etc. - Ray Charles
Romeo & Juliet Theme (A Time For Love), Willow Weep For Me, Godfather Theme, others & Doc Severinson lp etc. - Henry Mancini
Mercy Mercy Mercy etc. - Buckinghams
Indian Reservation etc. - Paul Revere & Raiders
Natural Man, Love Is A Hurtin' Thing, Unforgettable, Your Good Thing etc. - Lou Rawls
John Gummoe's Rhythm Of The Rain - Cascades
Song Of Innocence - David Axelrod I Was Made To Love Her - Stevie Wonder

That's not halfway down the page of tittles.
"dano" is her Danelectro Bass, sounds different.
At some point she used masking tape to mute the strings, innovations to give the producers the sound they were looking for.

For more on Carol Kaye and other session artists that really played on alot of famous records look for The Wrecking Crew documentary.

Carol is still around, teaching now. One of my ham friends, a guitarist, is from southern California, and has met her. I follow the Wrecking Crew on Facebook; it's very interesting.