Duck is not as popular on menus as chicken. A joke was posted on the newsgroup za.humour on May 15, 1997:
 
“Prince Phillip is in Pretoria on Commonwealth business, and is invited to dine at that city’s most splendid hostelry. He scrutinises the menu, calls the waiter over and asks ‘what’s the duck like?’. The waiter replies “she is like the chicken but she swims.’”
 
The joke appears to come from South Africa. “A ‘new’ flight attendant is asked ‘what’s the duck like?’ and replies (of course in exaggerated African accent) ‘the duck he is like the chicken, but he swims’” was printed in the book Jetlag: SA Airways in the Andrews Era (2001) by Denis Beckett.
   
Irish radio and television broadcaster Terry Wogan (1938-2016) is often credited with the joke. He wrote in the column “Wogan’s World” in The Sunday Telegraph (London, UK) on April 30, 2006:
   
“Which reminds me of the tale of a traveller on an Irish airline who, when offered lunch by the stewardess, asked what was on the menu. ‘Well, there’s beef, salmon, chicken or duck,’ she told him. The passenger thought for a moment. ‘What’s the duck like?’ he asked. ‘It’s like a chicken but it swims…’”
   
       
Wikipedia: Terry Wogan
Sir Michael Terence Wogan KBE DL (/ˈwoʊɡən/; 3 August 1938 – 31 January 2016) was an Irish radio and television broadcaster who worked for the BBC in the UK for most of his career. Between 1993 and his semi retirement in December 2009, his BBC Radio 2 weekday breakfast programme Wake Up to Wogan regularly drew an estimated eight million listeners. He was believed to be the most listened-to radio broadcaster in Europe.
   
Google Groups: za.humour
Prince Phillip dines out in Pretoria
Bob Dubery
May 15, 1997, 3:00:00 AM
Prince Phillip is in Pretoria on Commonwealth business, and is invited to dine at that city’s most splendid hostelry.
 
He scrutinises the menu, calls the waiter over and asks “what’s the duck like?”.
 
The waiter replies “she is like the chicken but she swims.”
       
Google Books
Jetlag:
SA Airways in the Andrews Era
By Denis Beckett  
London, UK: Viking
2001
Pg. 10:
A ‘new’ flight attendant is asked ‘what’s the duck like?’ and replies (of course in exaggerated African accent) ‘the duck he is like the chicken, but he swims’.
 
Newspapers.com
30 April 2006, The Sunday Telegraph (London, UK), “Wogan’s World” by Terry Wogan, pg. 22, cols. 2-3:
Which reminds me of the tale of a traveller on an Irish airline who, when offered lunch by the stewardess, asked what was on the menu. “Well, there’s beef, salmon, chicken or duck,’’ she told him. The passenger thought for a moment. “What’s the duck like?’’ he asked.
 
“It’s like a chicken but it swims… ‘’
 
1 April 2007, The People (London, UK), “Comedi Vans” by Rachael Bletchly,  pg. 8:
MAN to Waitress: “What’s the duck like?” Waitress to Man: “Like chicken, but it swims, sir.”
     
Google Books
Orion’s Cartwheel
By Lawrence Winkler
Victoria, BC: First Choice Books
2012
Pg. 246:
Years after I left, Prince Phillip was offered a choice of the duck or the beef.
 
“What’s the duck like?” He inquired.
 
“It is like a chicken, only it swims.” Said the black waiter.
 
Google Books
The Wicked Wit of Ireland
By Myles Byrne
London, UK: Michael O’Mara Books Limited
2019
Pg. ?:
‘A stewardess of Aer Lingus asks a passenger if he’d like lunch. “What’s on the menu?” he asks. “Well, there’s chicken, beef, salmon or duck.” “What’s the duck like?” “It’s like a chicken but it swims.”’
TERRY WOGAN
 
Twitter
Phil Wharton
@PhilWharton66
Terry Wogan joke. Passenger asks aer lingus stewardess what’s on the menu. She says beef, chicken, lamb and duck. Bloke says what’s the duck like? She says it’s like the chicken but it swims.
Erin go bragh
9:20 AM · Mar 17, 2019·Facebook
 
Twitter
Aman Singh
@AmanTSinghZA
Replying to @NatalieGov_
What’s the duck like?
It’s like the chicken..
But it swims
I quack me up
5:49 AM · Dec 24, 2019·Twitter for Android
   
Twitter
Epic Crescendo
@epiccrescendo
☘ “A stewardess of Aer Lingus asks a passenger if he’d like lunch. ‘What’s on the menu?’ he asks. ‘Well, there’s chicken, beef, salmon or duck.’ ‘What’s the duck like?’ ‘It’s like a chicken but it swims.’” ☘
~ Terry Wogan
5:48 PM · Mar 17, 2021·Twitter for Android
 
Twitter
mariana Z
@mariana057
So I said to the waitress: “What’s the duck like?”
She said: “Like a chicken, but it can swim”.
9:16 PM · Apr 12, 2021·Twitter for iPhone
       
Twitter
Yorkie ‘B’ RN VD and Scar..
@RenownVet01
So I said to the waitress: “What’s the Duck like?”
She said “Like a Chicken, but it can swim”.....
10:01 AM · Apr 18, 2021·Twitter for Android
   
Twitter
𝗧𝗮𝗱𝗶𝗶® | Heavy multiplication x | ⓩ Waving black flag
@BitFlexJack
Walks into Restaurant….
Sits down….
Waiter brings the menu and says - “Today’s special is Duck in Oyster Sauce”
Me: What’s the duck like?
Waiter: Well…. The Duck…. She’s like a chicken…. But she swims….
I died…..
4:25 PM · Aug 7, 2021·Twitter for iPhone
 
Twitter
mariana Z
@mariana057
So I said to the waitress: “What’s the duck like?”
She said: “Like a chicken, but it can swim”.
2:30 PM · Aug 11, 2021·Twitter for iPhone
   
Twitter
вєαя
@BigBearF1
So I said to the waitress: “What’s the duck like?”
She said: “Like a chicken, but it can swim”.
6:24 AM · Nov 23, 2021·Twitter for iPhone
 
Twitter
Robert Wilkinson
@robertwlk
I said to the waiter; “What’s the duck like?”
Waiter; “Like a chicken but it can swim.”
2:04 PM · Nov 26, 2021·Twitter for Android