Octavio Briswald’s field notes, September 26, 2115
In those echoing caverns, the noise they make is incredible—a slithering, writhing hissing, a deafening whisper, feathers gliding over feathers as necks and bodies circumnavigate each other in endless spirals.
In those yawning caverns, plurality rules supreme; the concept of monogamy would be foreign and abhorrent, except that it is never considered at all. The birds move as one great heaving unit, partnering to the left, then the right, and then back to a new partner on the left. Fidelity is for the group at large; competition is left exclusively to the spermatozoa. Let the gametes fight it out, the birds seem to say. For now, this joy is all.
In those capacious caverns, the sense of culmination is palpable. This is the moment toward which the last eleven years have driven: the fevered writhing, the sudden lull, and then—yes!—the squelching plop of hundreds of eggs laid simultaneously.
The adults clamber back to the cavern’s entrance, blinking in the glare of the sun. Within a week, they will all be dead. For a month or more, no eel-birds fly above the surface of Regulus V.
And then the new generation cracks free from their shells, blinking in miniature at the sun, ready to begin the cycle anew.
Other mentions: Spock referred to eel birds while attempting to explain the Vulcan mating ritual pon farr. (TOS)