The most common and most likely answer to this crossword clue is the 4 plus 6 letter word DAWN CHORUS
I've seen this crossword clue in The Guardian
D
A
W
N
C
H
O
R
U
S
More clues leading to the result DAWN CHORUS
- What you get up to in the way of tweeting
- Draw on such training for early performance?
- Turned sunward outside chapter house for early morning song
- Initially, what intrudes upon rest at start of day? Us!
- In brief half-light, stop to catch first bit of warbling — like this?
- Crown had crazy American tweets galore
- Arousing songs?
- Rousing songs
- Cheep alarm clock?
- Early music without instrumentation
Buddy explains!
The straight part
We know that "early morning song" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case early morning song = dawn chorus.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.