Of, pertaining to, or having to do with birds;
avian; birdlike.

Avine and Volucrine are two terms identical in meaning. Different roots, Aves and Volucer respectively, but the same definition. Oh, one could go ahead and add in: Resembling, or having the characteristics of, birds, but that is what birdlike is for.

So, why have all these words for avian? One could probably make a compelling argument for convergent evolution within a living language, especially pre-internet when instantaneous publication to a global audience wasn't yet an everyday thing. But, no, one would be wrong. It's for rhythm and rhyme in poetry, of course! And, for those in prose, be it for speculative, factual, or world-building purposes, currently existing words help with plausibility, credulity, and continuity, amongst other things.
(Don't forget the art of pun!)

As birds of a feather flock together, more specific adjectives for different types of birds have been curated and alphabetized below for ease of use.

Adjective - Bird

Accipitrine -Hawk
Anatine - Duck
Anserine - Goose
Aquiline - Eagle
Buteonine - Buzzard
Cathartine - Condor
Ciconine - Stork
Columbine - Dove
Corvine - Crow, Raven
Cuculine - Cuckoo
Cygnine - Swan
Cypseline - Swift
Didine - Dodo
Emberizine - Bunting
Falconine - Falcon
Fringilline - Finch
Galline - Chicken
Hirundine - Swallow
Icterine - Meadowlark
Larine - Gull
Milvine - Kite
Mimine - Mockingbird
Oscine - Songbird
Passerine - Sparrow
Pavonine - Peacock
Perdicine - Partridge
Phalacrocoracine - Cormorant
Phasianine - Pheasant
Picine - Woodpecker
Psittacine - Parrot
Pullastrine - Pigeon
Pyrrhuloxine - Cardinal
Scolopacine - Snipe
Struthionine - Ostrich
Trochiline - Hummingbird
Turdine - Thrush
Vulturine - Vulture

No animals were harmed in the writing of this node,
as birds aren't real.