Domestic rabbits show behaviors that are sexually dimorphic with respect to motor pattern and/or hormonal responsiveness, e.g., scent-marking, mounting, and maternal nest-building. Whether these sexual dimorphisms depend on sex-typical organization of the nervous system during development or on their activation by particular hormones during adulthood, is little understood. Maternal nest-building occurs in mid- late pregnancy and involves: digging, straw-carrying, and hair-plucking. These behaviors depend on the continuous action of estradiol but their sequential timing is dictated by the presence and subsequent absence of progesterone (P). We explored nest-building in buck rabbits to determine: a) if the neural substrate controlling this behavior is defeminized across male-typical development; b) if such behavior can be used as a model to explore P actions on the male mammalian brain. Bucks castrated during adulthood and receiving estradiol benzoate (EB) + P dug significantly more than when given oil. Straw-carrying significantly increased following P withdrawal (6/17 bucks) and was not expressed under oil treatment (0/17). Hair-plucking occurred after P removal (4/17 males). Bucks castrated before puberty and given EB+P showed nest-building behaviors in the same proportion as males castrated in adulthood. Results show that some castrated bucks can express a ‘gender-atypical’ behavior, regulated by estradiol and P, thus suggesting that: a) rabbit brain sexual differentiation does not necessarily involve a suppression of responsiveness to estradiol and P; b) maternal nest-building in bucks provides a reliable model for exploring the ways by which P modulates brain functions in male mammals.