Answer:
Option C, adaptive function
Explanation:
A Male Australian bowerbirds builds a distinctive nest which is attractive enough to attract a mating partner. Here the bowerbirds is adapting to the environment without affecting others but enhancing its own chances of survival and reproduction. So here we can say that male bowerbirds uses its brain and cognitive systems to build bowers thereby giving rise to behavioural competition thereby establishing behaviorally conditioned reproductive isolation
Hence, option C is correct