Bestiary of Resonant Fauna

The Bestiary of Resonant Fauna is an illustrated taxonomic register, held in the Scriptorium of the Seventh Spiral, describing those species whose bodies produce, retain, or return sound in ways the Tower considers administratively significant. It is an annex to the Third Concordance and, since its second recension of 1,142, has served as the working reference for Residual Echo Mapping as practised under the Field Guide to Unseeable Fauna. Unlike the Theoretical Bestiary, which catalogues fauna postulated to exist by necessity, the Bestiary of Resonant Fauna concerns itself only with creatures whose acoustics have been observed, measured, and entered in a ledger. Entries are arranged by resonance class rather than by lineage, a decision that has caused more dispute than any other feature of the document.

Scope and method

The Bestiary recognises four resonance classes, designated alpha through delta. Alpha species emit sound deliberately; beta species retain it after the emitter has departed; gamma species return it altered; delta species are silent but measurably resonant, in the manner of a struck vessel. Each entry records the specimen's class, its observed frequency range in the Tower's own tuning, the number of accessioned individuals, and the floor or floors on which it has been confirmed. The current register runs to two hundred and eleven entries, of which forty-one are marked provisional — a designation introduced in the fourth recension to quiet an argument about the Echo-Hawk and never subsequently withdrawn.

Field method is prescribed in the Bestiary's prefatory matter: an observer must record a specimen's call twice, once at the aperture and once three floors distant, and must note any discrepancy between the two without attempting to explain it. The instruction is repeated in Ordinance on Non-Catalogued Fauna, which extends it to species not yet entered, on the reasoning that an unexplained discrepancy is easier to accessioned than a corrected one.

The Echo-Hawk

The Bestiary's most cited entry is the Echo-Hawk, a raptor of the upper reaches whose specialized syrinx permits it to reproduce a call heard up to nine days earlier. The entry describes the syrinx in detail and includes a folding plate, now much repaired, showing the organ in section. The Echo-Hawk's calls are the principal calibration signal for Residual Echo Mapping, and the Field Guide to Unseeable Fauna directs surveyors to compare their readings against a recorded Echo-Hawk call before entering any floor above the Twentieth Spiral. The bird is classed as fauna in its own right, and also appears in the Bestiary of Unseen Behaviors in connection with a ritual of silent return observed at the Delta Aperture.

"The Echo-Hawk does not answer. It repeats, and the repetition is the answer, and the surveyor who waits for a third call will wait past the closing of the stair."

— Field Guide to Unseeable Fauna, section 9, "On Patience"

Disputed entries and the Vorn question

The Bestiary's treatment of the Index Hawk is the occasion of its longest-running scholarly quarrel. The Bestiary of Resonant Fauna lists the Index Hawk as a beta species of low resonance, retained chiefly for the sound of its wingbeats over catalogue drawers. The Vorn Criterion, however, holds that a creature whose resonance is incidental to its function should not be entered at all, and a faction of cataloguers has argued since 1,207 that the Index Hawk's entry ought to be struck. The Librarians have declined to strike it. Citing the Bestiary's own prefatory rule — that a species is resonant if the Tower has heard it — they have left the entry in place and added a marginal note reading, in the hand of the period, "It has been heard."

A similar dispute concerns the register's treatment of implied species. Project GIFT and its Great Taxonomy of Implied Fauna formally segregate Implied Fauna from Archival Fauna, and the segregation has never sat comfortably with the Bestiary, whose resonance classes were devised for creatures that can be recorded. The Bestiary's fifth recension attempted a compromise, admitting implied species to the delta class on the grounds that a creature never heard is, acoustically, indistinguishable from a silent one. The Project GIFT register rejected the reasoning; the Bestiary's editor at the time, Precentor Mavel Ash, defended it in a memorandum now bound into the front matter, and the two documents have contradicted one another quietly ever since.

The Ash grievance and the fourth recension

The Bestiary's history is inseparable from the feud between its scriptorium and the Office of Sustenance. In the winter of 1,144, following the enshrining of Archival Fauna as entities entitled to sustenance under Concordance 44, the Office began issuing provision orders for every creature the Bestiary listed, on the assumption that a listed species was an accessioned one. The Bestiary had never claimed as much. Its entries included creatures observed once and never again, creatures known only from the sound of them, and at least one entry — the Lesser Bell-Crab of the Ninth Spiral — describing an animal that turned out to be a door.

Ash protested the provision orders in a memorandum to the Office, arguing that "a register of sounds is not a roll of mouths" (Precentor Mavel Ash, memorandum of 12 Frost, 1,144). The Office replied that it had no other roll to work from, and that the Bestiary's own frequency measurements were the only reliable means of identifying which creatures were which. The dispute was settled by amendment rather than argument: the fourth recension added the provisional marker, and the Office agreed to suspend provision orders for provisional entries pending confirmation. Forty-one entries have remained provisional since. The Lesser Bell-Crab's provision order was withdrawn in 1,146, and the door has not been heard from since.

Relationship to other registers

The Bestiary sits at an awkward junction of the Tower's taxonomic documents. It shares species with the Theoretical Bestiary, the register of custodial fauna, and the symbiotic register, and its editors have never agreed with any of them about where a given creature belongs. The ambient fauna schedules draw heavily on its delta class, while the upper-reaches survey treats its Echo-Hawk entry as authoritative and its other entries as indicative only. The Department of Metaphorical Fauna has twice requested the transfer of three entries it considers improperly literal; both requests were refused on the grounds that the Bestiary does not adjudicate meaning, only sound.

Copies of the Bestiary are held on four floors. The Seventh Spiral copy is the working text and is annotated; the copy on the Thirty-Third is considered the most accurate but is chained; the copy on the Second Spiral is incomplete; and the copy on the floor whose number is disputed is not consulted. Readers wishing to hear a specimen are asked to submit a request to the scriptorium in writing and to wait for the next scheduled survey. The scriptorium does not accept requests submitted in person, as the sound of the door interferes with the register.