Obsession of northern Arab stuffing extinct bird (9)
I believe the answer is:
monomania
'obsession' is the definition.
(I've seen this before)
'northern arab stuffing extinct bird' is the wordplay.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'arab' becomes 'omani' (Omani is an example).
'stuffing' means one lot of letters goes inside another.
'extinct bird' becomes 'moa' (extinct flightless bird of New Zealand).
'n'+'omani'='nomani'
'nomani' inserted inside 'moa' is 'MONOMANIA'.
'of' is the link.
(Other definitions for monomania that I've seen before include "obsessive single-mindedness" , "Unhealthy preoccupation with one thing" , "Obsession with one thing" , "Single-minded passion" .)