Vad är den fågeliknande varelsen på Two Towers J.R.R. omslag?

Det var en av Nazgûl, som anges i kapitel 11 i bok 3, The Palantir . Även om själva varelsen (som nämnts av @vsz i kommentarerna) är en av de fåglar, eller helvetehuggarna 1 , som riddes av Nazgûl efter händelserna vid Fords of Bruinen.

At that moment a shadow fell over them. The bright moonlight seemed to be suddenly cut off. Several of the Riders cried out, and crouched, holding their arms above their heads, as if to ward off a blow from above: a blind fear and a deadly cold fell on them. Cowering they looked up. Avast [sic] winged shape passed over the moon like a black cloud. It wheeled and went north, flying at a speed greater than any wind of Middle-earth.

[...]

Nazgûl!’ he cried. ‘The messenger of Mordor. The storm is coming. The Nazgûl have crossed the River! Ride, ride! Wait not for the dawn! Let not the swift wait for the slow! Ride!
The Lord of the Rings: The Two Towers - Chapter 11, The Palantir

Nazgûl flyttade mot Orthanc från Minas Morgul.

Från Interaktiv karta på LotR Project kan vi se det den 5 mars när de camping på Dol Baran , och Nazgûl" körde norrut "mot orthanc

Några citat för att stödja ovanstående finns i två tornen och årets tal.

Winged Nazgûl passes over the camp at Dol Baran.
The Lord of the Rings: The Return of the King - Appendix B, The Two Towers

Less than an hour had passed, and they had reached the Fords of Isen and crossed them. The Mound of the Riders and its cold spears lay grey behind them.

Betalningar till @MartinSmith för namnet på varelsen.

De andra svaren anger att detta är en Nazgûl (AKA Ringwraith, Black Rider, Dark Rider)

@vsz påpekar

Isn't the Nazgûl the name of the guy riding on the flying beast, instead of the flying beast itself?

Det verkar att det inte finns ett kanoniskt namn för de varelser som Nazgûl flög på.

Wikipedia-stater

After losing their horses at the Ford of Bruinen, the Nazgûl returned to Mordor and reappeared mounted on hideous flying beasts; Beregond called them "Hell Hawks". Tolkien describes them as "fell beasts", though Tolkien applies the adjective fell ("fierce, cruel") to a variety of other creatures throughout The Lord of the Rings — even at one point to Gandalf. In a letter, he calls the winged mounts "Nazgûl-birds". In the absence of a proper name, derivative works sometimes press "fellbeast" or "fell-beast" into service.

LOTR-wiki diskuterar även detta i dess artikel om Fellbeast

There is a common misconception that these creatures are called Nazgûl, probably due to the fact that the unit in many video games (combined Fell beast and Ringwraith) was called a Nazgûl...