Aerial Fauna of the Upper Reaches

The Aerial Fauna of the Upper Reaches comprises all uncatalogued and provisionally catalogued flying, drifting, and suspended animal populations observed between Floor 10,000 and the uppermost recorded galleries of The Upper Reaches. The designation is an administrative one rather than a taxonomic one: a creature enters the class by occupying airspace above Floor 10,000 that is not already assigned to a named transit corridor, and it leaves the class the moment it settles, dies, or is claimed by a floor. The category was formally opened under Annex D of the Upper Reaches Cataloguing Project and remains the only annex of that project whose inventories are issued quarterly rather than annually.

Aerial faunal survey in the Upper Reaches is conducted by the Allegorists of the Upper Reaches in cooperation with the Upper Scriptorium, which holds the definitive textual authority for administrative law in the Upper Reaches and therefore the definitive word on what counts as airspace. Practical coordination falls to the Bureau of Elevated Archives, whose field observers are the only personnel licensed to record an aerial specimen without first obtaining an Bureau of Permissions Amp Transit certification for vertical approach.

Scope and definition

The Upper Administration governs aerial fauna under the Twenty-Second Concordance, which defines an aerial specimen as "any animate body whose customary altitude exceeds its customary floor." This definition has proven durable but porous. Sedentary species that roost above Floor 10,000 remain aerial by custom so long as they are capable of flight, which places several largely motionless populations — notably the suspended thrush and the mooring wren — within the class despite their never being observed in motion by a survey team.

The Custodial Fauna, Symbiotic Fauna, and Passive or Ambient Fauna categories each overlap the aerial class at their edges. Where an aerial creature is found to perform a custodial function, precedence is granted to the older category and the specimen is recorded in the aerial register only as a cross-reference.

Principal populations

Survey returns for the period 12,411–12,598 record four principal populations, here given in descending order of recorded biomass:

• Ledge kites — long-bodied gliders that circle the gallery voids between Floors 10,200 and 11,040. Ledge kites are the only aerial fauna with a documented nesting cycle tied to the Upper Register, which they line with withdrawn parchment.
• Transit gulls — opportunistic, aggressive, and strongly associated with the Aerial Causeways and their approach ramps. Transit gulls have been the subject of nine separate acoustic complaints filed under the Historical Commissioner's standing resolution on transit noise.
• Upper drift moths — dust-coloured, non-directional flyers that travel on the thermal columns rising from the lower floors. They are catalogued aerially despite being incapable of sustained flight, on the grounds that they are rarely observed on any surface.
• The ascending heron — a single-specimen population, recorded at Floor 12,433 in the third quarter of 12,441 and at Floor 12,517 in the first quarter of 12,442. No second heron has been logged.

Additional taxa are treated in the Field Guide to Unseeable Fauna, which records eleven aerial species known only through the disturbances they leave in draught patterns.

Ledge kites and the Register question

The ledge kite's use of withdrawn parchment has generated the most sustained scholarly disagreement in the aerial literature. Under the Nineteenth Concordance, material removed from the Upper Register remains administratively live until it is formally retired. Those who read the Nineteenth strictly argue that a kite's nest is therefore an unauthorised filing point and must be dismantled and its contents reinstated. Those reading the Thirty-First Concordance counter that live material incorporated into an animal structure passes to custodial jurisdiction, and that dismantling constitutes interference with a Custodial Fauna population.

"The kite does not remove the leaf. The kite receives the leaf and the Tower does not lose it. The argument is about the word nest."

— Annotation to the Thirty-First Concordance, Upper Scriptorium copy, marginal hand unrecorded

No resolution has been published. In practice, nests are surveyed and left standing, a position described in the Upper Reaches Cataloguing Project's interim memorandum as "tolerated pending amendment."

Population counts and the drift-moth discrepancy

Aerial censuses are conducted by timed visual sweep from fixed gallery stations. This method is reliable for kites and gulls and demonstrably unreliable for drift moths, whose density varies with thermal output from floors well below the survey boundary. Two competing correction factors are in use. The Stratigraphic Repository for Non-Conforming Aesthetics applies a factor of 1.4 derived from its own draught records; the Scriptorium applies no factor at all and dismisses the Repository's figure as "an aesthetic inference dressed as arithmetic."

The discrepancy is substantial. Quarterly returns for 12,570 give 41,000 drift moths under the Repository method and 29,200 under the Scriptorium method, against a total aerial biomass figure that both parties agree upon to within four per cent. The Twenty-Second Concordance is silent on which count governs for purposes of the annual return.

Hazards and transit regulation

Transit gulls constitute the principal collision hazard on the Aerial Causeways between Floors 10,000 and 11,200. Under the Bureau of Permissions Amp Transit's standing circular on vertical approach, causeway operators are required to log gull strikes but not to abate them, a distinction that has been contested by three successive operators and upheld twice. The Historical Commissioner's acoustic resolution, originally framed for disputes in the Upper Reaches generally, has been extended to cover gull vocalisation on nine occasions.

The ascending heron is the subject of a standing caution rather than a regulation. Operators are asked to report sightings and to take no other action. Records as of the last full audit stand at one specimen, twenty-eight sightings, and no conclusion.

See also

• Field Guide to Unseeable Fauna
• Custodial Fauna
• Symbiotic Fauna
• Passive or Ambient Fauna
• Aerial Causeways
• M. Thorne