Why does the herding of caribou increase their likelihood of successful reproduction?

Responses
A Herding behavior decreases competition for food.

Herding behavior decreases competition for food.
B Herding behavior reduces spreading of viral diseases.Herding behavior reduces spreading of viral diseases.
C Herding behavior makes parasitic infection less likely.
Herding behavior makes parasitic infection less likely.
D Herding behavior allows for more awareness of a predator than solitary behavior.

Herding behavior allows for more awareness of a predator than solitary behavior.