refers to births. Specifically, it refers to the birth rate of an animal, while mortality specifically refers to the death rate.

the ratio of live births in an area to the population of that area; expressed per 1000 population per year

Birth as a component of population change.

The frequency of deaths as a component of population change.

Births as a component of overall population change. The term is often used interchangeably with fertility.

natural ability of a population to increase (reproduce).