Also known as Tinfang Gelion, this is originally some sort of fairy bird (a leprawn), first appearing in two early poems (1914) of J.R.R. Tolkien: "Tinfang Warble," written 1914, and published in a rewritten form circa 1927; and "Over Old Hills and Far Away," written 1915. Both were collected into The Book of Lost Tales Part One (1983).
Tinfang Gelion who still the moon
enchants on summer nights of June
and kindles the pale firstling star;
and he who harps upon the far
forgotten beaches and dark shores
where western foam for ever roars,
Maglor whose voice is like the sea;
and Dairon, mightiest of the three.