As the editor of TLL proposes (corroborated by additional glosses), this word is probably a corruption of laner1 ('lanner falcon'), possibly through scribal association with ane1 ('duck').
a.
faucon anier
1falc.orn.(in error?) falcon for duck hunting (?):
(
1302-05
)
celx qui gardent nos faucons [...] aniers
498
s.
1orn.falc.(in error?) falcon for duck hunting (?):
(
MS: s.xii/xiii
)
falco peregrinus, falco assensor[i]us, tardarius gloss: aner (ed. [l]aner), prepes, infestus [...]
i 182.65 and ii 87.65
anier (s.xii/xiii)