The characteristic that kosher chickens or birds must adhere to is that only certain species are allowed. In Judaism, kosher dietary laws, known as kashrut, outline specific criteria that must be met for an animal to be considered kosher. For birds, the Torah specifies which species are permissible, and traditionally, this includes domesticated birds like chickens, turkeys, ducks, and pigeons, among others.
This selection is vital in ensuring that the poultry aligns with Jewish dietary laws. The guidelines do not merely dictate how animals should be treated or prepared; rather, they specify the types of animals that can be consumed in accordance with religious commandments.
The other options, while they touch on aspects of poultry consumption, do not accurately reflect the stringent requirements of kashrut as they pertain specifically to kosher birds. For instance, while kosher birds must be processed correctly, the preparation rules (like cooking) do not necessarily hinge on the bird itself being inherently kosher or not. Similarly, issues of captivity do not apply to kashrut, as the primary concern is whether the species itself is deemed permissible for consumption.