Neiirrhs were a type of small birds that lived on the Romulan homeworld of Romulus. The small avians possessed a brilliant plumage but this hid its deadly poison spurs which it used to kill its prey. Typically, a swarm of these birds were capable of killing a lone adult Romulan.
Hiren kept an aviary filled with these birds which he unleashed on Praetor of the Romulan Star Empire Neral, who died from the poison of the birds, allowing Hiren to rise to the status of Praetor. (TOS - Vulcan's Soul novel: Epiphany)