Colloquial Terms: The Convocation, The Storm, The Flock, Thunderbirds, Ziz, Roc, FEATHERED
Physical Characteristics: Appears as a large group of birds of various species. Mysterious "giant birds" have reportedly been sighted among large enough gatherings (NOTE: Archive Analysts believe those giant bird manifestations to be the inspiration for all sorts of legends, ranging from Thunderbirds to Rocs. --SΣ)
Behavioral Characteristics: Despite being spread over numerous bodies, it appears to possess only one mind. In large gatherings, static is often observed being discharged into the air. Has been known to attack humans. Sometimes observed leaving threatening messages for the intended victim, usually through the use of a human servant. Servants are used as nests, keeping birds within their own bodies.
Servants (NOTE: Or "nests" --SΣ) of PRE13 are designated under the P13A00 series.
Further Reading: The blog "The Darkling Thrush", as well as this story here.