Old picture in ecclesiastical books primarily found in ordinals (3,5)
I believe the answer is:
the birds
'old picture' is the definition.
(Alfred Hitchcock film)
'ecclesiastical books primarily found in ordinals' is the wordplay.
'primarily' suggests taking the first letters.
'found in' means one lot of letters goes inside another.
'ordinals' becomes 'thirds' ('third' is the ordinal form of the number 3).
The initial letters of 'ecclesiastical books' is 'eb'.
'eb' inserted into 'thirds' is 'THE BIRDS'.
'in' is the link.
(Other definitions for the birds that I've seen before include "Greek drama" , "1963 Hitchcock film" , "Old film" .)