In Seabirds: an Identification Guide (1983), Peter Harrison has utilized
jizz under his abbreviation of FHJ (Flight, Habits, and Jizz) that he
includes in the discussion of each bird species. He talks about it in
the introduction: "Jizz is not created by any particular feature of
plumage, nor by behavioural traits or even by shape, though much does depend
on shape...Despite its abstract connotations, jizz can enable a bird to
be recognized instantly without recourse to critical examination of such
things as wingtips etc., and this is one of the most important characters
to look for."

Tom Weir
weir at u.washington.edu
(206)747-8480