Donkeys, like many mammals, often give birth during the nighttime hours, and this timing appears to be linked to hormonal regulation, specifically the hormone melatonin.
The Role of Melatonin in Nighttime Births
The phenomenon of donkeys and other mammals giving birth at night is closely associated with the body's natural circadian rhythms and the production of melatonin.
- Melatonin Production: The brains of most mammals produce melatonin primarily in the late evening. This hormone is well-known for its role in regulating the sleep-wake cycle, signaling to the body that it's time for rest.
- Increased Sensitivity Near Birth: As the time for giving birth approaches, levels of melatonin in the bloodstream increase. Furthermore, the receptors for melatonin on the uterus also become more numerous, enhancing the uterus's sensitivity to the hormone.
- Impact on Birth Canal Muscles: This increased sensitivity means that the muscles in the birth canal become more responsive to melatonin's presence. While the exact mechanism is complex, the timing correlated with higher nighttime melatonin levels is believed to contribute to the initiation or progression of labor during this period.
Essentially, the body's natural nighttime production of melatonin, combined with heightened sensitivity in the reproductive system, creates conditions favorable for labor and delivery to occur after dark.
This natural timing might offer evolutionary advantages, such as reduced risk from predators during vulnerable labor and delivery periods, or simply align with the mother's natural rest cycle.