Hormones and external factors: are they "on/off" signals for maternal nest-building in rabbits?

Estradiol, progesterone, and prolactin regulate digging, carrying straw, and plucking hair for maternal nest-building in rabbits. To explore whether external factors also modulate this process, we assessed whether shaved pregnant rabbits with straw nests would collect their own, male, or synthetic hair for nest-building. Pregnant (but not estrous) does collected and used all hair types, indicating that hair-plucking can be bypassed and a nest constructed with "alternative" hair. Unshaved pregnant does with straw nests also collected synthetic hair, indicating that this behavior is not triggered by the absence of maternal hair. Yet, if hair-plucking/nest-building had occurred, hair-collecting was prevented, suggesting that an internally triggered "drive" was turned off by perceiving a built nest. When given only straw or hair, shaved pregnant does collected and used the material provided, indicating that nest-building is internally driven and accomplished by using any available elements. When given both materials, increasingly more shaved does built straw nests across prepartum days 7 to 2. Straw-carrying declined thereafter, suggesting that perceiving a straw nest limits the collection of such material. Hair-collecting was postponed until prepartum day 1 to postpartum day 2, indicating that: (a) mothers distinguish between straw and hair and (b) hormonal factors regulate the sequential selection of straw and then hair and when the change from straw to hair occurs. Maternal behavior was normal at parturition and for the next 4 days in a similar proportion of does among all experimental groups. We conclude that hormones and external factors regulate nest-building by acting as "on/off/on" signals.