Na population of doves in a forest, a small group of long-tailed doves migrates to another forest. over successive generations, the population in the new habitat shows more of the long-tailed doves than the short-tailed ones. which factor could be responsible for this microevolution?

Founder Effect

Explanation:

The genetic progression mechanism "founder effect" occur when a certain characteristics or traits in a given population arises because of  a group of organism that once was a part of main group (currently separated from the main group)but now has also become a part of the newly established colony.

This effect usually occurs in population lacking genetic variation due to small mating population and hence the genetic diversity decreases sharply.

Here, population of doves with long-tails starts arising in a given population after successive generations. Hence, it is also due to founder effect.