Answer:
The correct option is C) genetic variation
Step-by-step explanation:
Genetic variation can be described as the differences present in the genetic material i.e DNA of organisms present in a population. Genetic diversity allows organisms of a species to better adapt to an environment. A population in which the genetic variability is scarce might become wiped out by a disease or an invading predator.
As the birds show different variations hence the term that best described them is genetic variation.