Bird made of silver unwanted at first in auction (7)
I believe the answer is:
seagull
'bird' is the definition.
(seagull is a kind of bird)
'silver unwanted at first in auction' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'at first' says to take the initial letters.
'in' indicates putting letters inside.
'auction' becomes 'sell'.
The initial letter of 'unwanted' is 'u'.
'ag'+'u'='agu'
'agu' put into 'sell' is 'SEAGULL'.
'made of' is the link.
(Other definitions for seagull that I've seen before include "Marine bird" , "Bird paradoxically fond of landfill sites" , "One sitting atop mast perhaps" , "Avian scavenger" , "Main creature" .)