From OpenStreetMap Wiki
- Because most other related tags have used the plural. They were merged into a single category, and a single "feature group" page (including for translations, except languages that don't distinguish singular and plural forms).
- Anyway this is a group name featuring many tags for many animals, not just one, even if there's a animal=* but it is not the only one, as seen here). — Verdy_p (talk) 13:07, 6 November 2016 (UTC)