Cockney's cry of distress encountering alien young bird (5)
I believe the answer is:
owlet
'young bird' is the definition.
(I've seen this before)
'cockney's cry of distress encountering alien' is the wordplay.
'cockney's cry of distress' becomes ''owl' ('howl' said with the 'H' dropped - a cockney accent.).
'encountering' means one lot of letters go next to another.
'alien' becomes 'et' (extra terrestrial).
'owl'+'et'='OWLET'
(Other definitions for owlet that I've seen before include "One may give a little screech" , "Wise young" , "Young hooter" , "Young bird; moth" , "Offspring of the wise one?" .)