We suggest that nest building activities themselves might keep circulating testosterone production elevated through a nest building 'self-feddback' mechanism on testosterone production, whose existence and mechanisms should be explored in future studies. 3/3

In this paper, we primarily demonstrate that circulating testosterone, whose level stays stable as long as male zebra finches build a nest, suddently drops once nest building is over, and this in abscence of any incubation. 2/3