Extinction is defined in biology and conservation ecology as the termination of a taxon by the death of the very last individual of that species.
When no living members survive anywhere on Earth (or in captivity), the species is declared extinct (e.g., Passenger Pigeon, Dodo, Tasmanian Tiger).

The concept of Biosphere Reserves was initiated by UNESCO in 1971 under its Man and the Biosphere (MAB) Programme.
The formal network of Biosphere Reserves was established in 1976 to promote a balanced relationship between humans and nature through three core zones: Core area (strictly protected), Buffer zone, and Transition area.

The gestation period of the greater one-horned rhinoceros (Rhinoceros unicornis, Indian rhino) is approximately 15.5 to 16 months (about 460 to 490 days):
Females give birth to a single calf at intervals of roughly 3 to 4 years.
In contrast, elephants have a gestation period of 20–22 months, while large felids (tigers) have a gestation period of around 3.5 months (105 days).

According to the UNESCO MAB zoning model for Biosphere Reserves:

• Core Zone: The strictly protected, inviolate natural area dedicated entirely to the conservation of habitats, species, and genetic variation. No human activity, settlement, or commercial exploitation is permitted, except strictly regulated, non-destructive scientific monitoring.
• Buffer Zone: Surrounds the core area where low-impact activities like research, education, controlled ecotourism, and managed grazing are permitted.
• Transition Zone (Manipulation Zone): The outer zone where sustainable agricultural, settlement, and economic activities take place.