The most common and most likely answer to this crossword clue is the 6 letter word PANDAS
I've seen this crossword clue in The Times
P
A
N
D
A
S
More clues leading to the result PANDAS
- Creatures unhappy to sleep upside-down
- Endangered animals face ruin without end
- Asians with empty accounts under pressure
- Reluctant breeders turn to gloomy snooze
- Animals in police cars
- Animals having unhappy sleep, rolling over
- Animals in the borders of plaza at Sweden
- Put down prosecutor’s animals
- Troubled sleep is over for bears
Buddy explains!

The straight part
We know that "Endangered animals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case endangered animals = pandas.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 PANDAS mean?
PANDAS noun- The red panda (Ailurus fulgens), a small raccoon-like animal of northeast Asia with reddish fur and a long, ringed tail.
- Short for giant panda.
- (law enforcement) Short for panda car.
- A brahmin who acts as the hereditary superintendent of a particular ghat or temple, and is regarded as knowledgeable in matters of genealogy and ritual.