Almost welcome capturing black bird (5)
I believe the answer is:
grebe
'bird' is the definition.
(type of bird)
'almost welcome capturing black' is the wordplay.
'almost welcome' becomes 'gree' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'capturing' means one lot of letters goes inside another.
'black' becomes 'b' (as in pencil classifications).
'gree' enclosing 'b' is 'GREBE'.
Can you help me to learn more?
(Other definitions for grebe that I've seen before include "Diving water bird" , "I'll dive in" , "Swimmer" , "Duck-sized water-bird" , "Diving waterbird" .)