“What did the buffalo say when his son left for college?”/“Bison!”

Parents say “goodbye” when their children are sent off to school, prompting a silly joke:
 
Q: What did the buffalo say when his son left for college?
A: Bison! (Bye, son!)
 
“What did the buffalo say to his son when he went away on a long trip?” was cited in a 1976 riddle book. “What did the buffalo say to her son when he left on the school bus?” was cited in 1997 newspapers.
 
   
Google Books
Biggest Riddle Book in the World, Part 2
By Joseph Rosenbloom
New York, NY: Sterling Publishing Company, Inc.
1976
Pg. 46:
What did the buffalo say to his son when he went away on a long trip?
“Bison!” (“Bye, son!)
   
Google Books
Big Book of Silly Riddles
By Brandreth Gyles.
New York, NY: Sterling Publishing Company, Inc.
1988
pg. 38:
What did the buffalo say to his son when he went on vacation?
Bison!
 
Google Books
December 1996, Boys’ Life, “Think & Grin,” pg. 61, col. 1:
Mike: What did the buffalo say to his son when he left on vacation?
Tim: I don’t know. What?
Mike: Bison.
—Alex Sullivan, Delta, Colo.
 
Google News Archive
27 September 1997, Gadsden (AL) Times,  “Mighty Funny’s Mini Jokes,” The Mini Page by Betty Debnam, pg. C1, col. 4:
Q: What did the buffalo say to her son when he left on the school bus?
A: “Bison!”
 
Google Books
Extremely Good Clean Jokes for Kids
By Bob Phillips
Eugene, OR: Harvest House
2001
Pg. 67:
Gilbert: What did the buffalo say when his son left for school each morning?
Gertrude: I have no idea.
Gilbert: Bison.
 
Twitter
Amber Choike
‏@amberchoike
What did the buffalo say when his son left for college?
http://twitpic.com/4hsz4
1:46 PM - 3 May 2009
   
Google Books
Jokes4Kids
By Paul G. William
Lulu.com
2013
pg. ?:
What did the buffalo say to his son when he went away on a trip?
Bye-son.
 
Twitter
sana
‏@woahsanaa
What did the Buffalo say when his son was leaving for college?🌚
Bison 🌝
3:09 AM - 26 Jun 2015