BirdSize.com combines measurements from structured datasets and other suitable reference sources to build bird size and morphology profiles.
Because different sources measure different characteristics, the source used for one field may not be the same source used for another field on the same species page.
Measurement Types
BirdSize may display body length, body mass, wingspan, wing length, bill measurements, tail length, tarsus length, Kipp’s distance, Hand-Wing Index, and other morphological fields when the underlying data support them.
These values are not interchangeable. Each measurement retains its own meaning.
AVONET Morphology Data
AVONET is used for a substantial portion of the site’s structured morphological data. Depending on the species record, these fields may include body mass, wing length, tail length, tarsus length, bill measurements, Kipp’s distance, and Hand-Wing Index.
AVONET wing length is treated as wing length. It is not presented as wingspan and is not doubled or otherwise converted into an estimated wingspan.
Wingspan and Body Length
Wingspan and broader body-length information may come from sources separate from morphology datasets. A species may therefore have a documented wing length but no published wingspan on BirdSize, or vice versa.
If a trustworthy wingspan value has not been documented for a species, BirdSize does not generate one from wing length.
Ranges and Representative Values
Many birds cannot be described accurately with one universal measurement. When available evidence supports a range, BirdSize may display minimum and maximum values rather than a single number.
Some visual comparison tools require a representative value in order to place an object on a common scale. Where this occurs, the representative value is a display tool for the comparison and does not replace the published measurement range.
Visual Scale
True-scale visual comparisons use the available biological measurement as the mathematical scale anchor. Images are resized proportionally rather than stretched to force them into predetermined dimensions.
A photograph or transparent bird asset does not by itself establish the real-world height or length of a bird. The biological measurement remains the source of scale.
Data Limitations
Measurements reported by different references may not match perfectly. Differences can result from sample size, sex, geography, population, subspecies, age, measurement technique, rounding, or the definition used by a particular source.
BirdSize aims to represent these limitations rather than hide them behind false precision.