50 Rupees - Elizabeth II Mauritius Kestrel

Mauritius issued this coin as part of a wave of conservation-themed commemoratives that swept Commonwealth nations through the mid-1970s, largely driven by the WWF and IUCN's push to attach endangered species to legal tender. The Mauritius Kestrel was an obvious candidate — by 1974, the wild population had collapsed to an estimated four breeding pairs, making it arguably the rarest bird on earth at that moment.

The recovery program, spearheaded by Carl Jones beginning in the early 1980s, would eventually bring the species back from that precipice. The coin predates that success by nearly a decade.