Maternal Nest-building Is Regulated By The Hormonal Actions Of Estradiol, Progesterone, And Prolacti

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Maternal nest-building is regulated by the hormonal actions of estradiol, progesterone, and prolactin. Given the importance of shelter to offspring survival and reproductive success, it is no wonder that a set of common hormonal signals has evolved. However, the exact timing and features of nest building vary among species, depending on endocrine and external factors.

The initial drive to perform this behaviour is stimulated internally via hormones specifically a rise in prolactin levels. This increase is driven by an increase in prostaglandin and a decrease in progesterone. The second phase of nest building is driven by external stimuli, this phase is also known as the material-oriented phase. In this stage it is said that external stimuli such as the proper nest building materials must be present. Both internal and external stimuli must exist in conjunction with one another for nest building to commence. The cessation of the nesting building is correlated with a rise in oxytocin which is the hormone responsible for the contraction of the uterus. Shortly after this, parturition will commence.

In rabbits, nest building occurs towards the last third of pregnancy. The mother digs and builds a nest of straw and grass, which she lines with hair plucked from her body. This sequential motor pattern is produced by changes in estradiol, progesterone, and prolactin levels. Six to eight days pre-partum, high levels of estradiol and progesterone lead to a peak in digging behavior. Both estradiol and progesterone are produced and released by the ovaries. One to three days pre-partum, straw-carrying behavior is expressed as a function of decreasing progesterone levels, maintenance of high estradiol levels, and increasing prolactin levels. This release of prolactin (from the anterior pituitary) is likely caused by the increase in estrogen-to-progesterone ratio. One day pre-partum to four days post-partum, hair loosening and plucking occur as a result of low progesterone and high prolactin levels, together with a decrease in testosterone. In house mice and golden hamsters, nest-building takes place earlier, at the start or middle of pregnancy. For these species, nest-building coincides with high levels of estrogen and progestin.

External factors also interact with hormones to influence maternal nest-building behavior. Pregnant rabbits that have been shaved will line their straw nest with available alternatives, such as male rabbit hair or synthetic hair. If given both straw and hair, mothers prefer straw during the straw-carrying period, and prefer hair during the nest-lining period. If given hair as the only material, shaved mothers collect the hair even when it is the straw-carrying period.

Interestingly, research on avian paternal behavior shows that nest-building is triggered by different stimuli in the two sexes. Unlike the case for females, male nest-building among ring doves depends on the behavior of the prospective mate rather than on hormonal mechanisms. Males that are castrated and injected daily with testosterone either court females or build nests, depending purely on the behavior of the female. Hence, the male avian transition from courtship to nest-building is prompted by social cues and not by changes in hormone levels.

Nesting instinct - Wikipedia
 

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