Birds together hide, conserving energy (5)
I believe the answer is:
skein
'birds together hide conserving energy' is the definition.
I can't judge whether this defines the answer.
'hide conserving energy' is the wordplay.
'hide' becomes 'skin' (a hide is an animal skin).
'conserving' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mc2).
'skin' going around 'e' is 'SKEIN'.
Can you help me to learn more?
(Other definitions for skein that I've seen before include "Coil of yarn - group of flying geese" , "Loose bundle of yarn" , "Flight of birds" , "A number of birds" , "Birds flying" .)