The most common and most likely answer to this crossword clue is the 6 letter word WARBLE
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The straight part
We know that "Call" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case call = warble.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 WARBLE mean?
WARBLE noun- The sound of one who warbles; singing with trills or modulations.
- In naval mine warfare, the process of varying the frequency of sound produced by a narrowband noisemaker to ensure that the frequency to which the mine will respond is covered.
- To modulate a tone's frequency.
- To sing like a bird, especially with trills.
- To cause to quaver or vibrate.
- To be quavered or modulated; to be uttered melodiously.
- A lesion under the skin of cattle, caused by the larva of a bot fly of genus Hypoderma.
- A small hard swelling on a horse's back, caused by the galling of the saddle.