The most common and most likely answer to this crossword clue is the 8 letter word ETHOLOGY
I've seen this crossword clue in The Times
E
T
H
O
L
O
G
Y
Buddy explains!
The straight part
We know that "Behavioural science" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case behavioural science = ethology.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 ETHOLOGY mean?
ETHOLOGY noun- The scientific study of human and animal behaviour.
- The study of the human ethos.