The most common and most likely answer to this crossword clue is the 5 letter word DODOS
I've seen this crossword clue in The Guardian
D
O
D
O
S
More clues leading to the result DODOS
- Old birds from two parties succeeded
- They all died taking too many drugs during parties
- Parties no longer in existence, proverbially
- Two parties with schemes to start with – but they were never going to fly!
- Old birds did initially love parties
- Bad odds — around zero — for these birds?
- Oh, Oh, stepping out of dog messes -- it's for the birds
- Odd shuffling very large old animals
Buddy explains!

The straight part
We know that "old animals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old animals = dodos.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DODOS mean?
DODOS noun- A large, flightless bird, †Raphus cucullatus, related to the pigeon, that is now extinct (since the 1600s) and was native to Mauritius.
- A person or organisation which is very old or has very old-fashioned views or is not willing to change and adapt.
- Fried plantain.