Headless dogs? They can be spotted in the sky (6)
I believe the answer is:
eagles
'they can be spotted in the sky' is the definition.
The definition suggests an adverb but the answer is not.
'headless dogs?' is the wordplay.
'headless' means to remove the first letter.
'dogs?' becomes 'beagles' (beagle is a kind of dog).
'beagles' with its first letter removed is 'EAGLES'.
Can you help me to learn more?
(Other definitions for eagles that I've seen before include "Birds with a sea leg?" , "Below-par" , "Golf scores of two under par" , "Keen-eyed birds" , "rock group?" .)