“Why do birds fly south for the winter?”/“Because it’s too far to walk.”

The classic question of “Why do birds fly south in the winter?” has a simple answer:
 
Q: Why do birds fly south in the winter?
A: Because it’s too far to walk.
 
The joke has been cited in print since at least 1933.
 
   
26 February 1933, The Sunday Star (Washington,DC), pg. 14, col. 4:
RIDDLES
4. Why do birds fly south in the Winter?—Ruth Ellen Alley.
ANSWERS.
4. Because it’s too far to walk.
 
29 February 1940, The Weekly Tribune (Moulton, IA), “Jokes” by Richard Davis, pg. 2, col. 6:
Miss Starr: Why do birds fly south in the winter time?
Norma Jean: I guess it’s because it’s too far to walk.
 
Google News Archive
15 September 1964, The Free Lance-Star (Fredericksburg, VA), ‘Fun Time—The Riddle Box,” pg. 12, col. 2:
Why do birds fly south when the winter comes?
Because it’s too far to walk.
 
Google Books
The Unique Animal:
The Origin, Nature & Consequences of Human Intelligence
By Don D. Davis
New York, NY: Prytaneum Press
1981
Pg. 146:
Question: Why do birds fly south?
Answer: Because it is too far to walk.

Google Groups: rec.humor
Minnesota Joke
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3/4/93
Q.  Why do birds fly south during winter?
A.  Because it’s too far to walk.
   
Google Books
The Mammoth Book of Jokes 2
By Geoff Tibballs
London: Constable & Robinson Ltd.
2012
Pg. ?:
Why do birds fly south in the winter?
Because it’s too far to walk.
 
Mostly True Stories of K. Renae P.
Ten Terrible Science Jokes
K. RENAE P. April 23, 2015
(...)
5. Why do birds fly south for the winter? Because it’s too far to walk.
 
Twitter
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JOKE: Why do birds fly south for winter?
Because it’s too far to walk! http://ift.tt/1aKpr0D
1:03 AM - 29 Jun 2015