The photoperiod is the time a Bearded dragon is exposed to light (vs. darkness) – over a period of 24 hours. When placed in an artificial environment, the photoperiod is an important factor to consider when trying to create a natural experience for Bearded dragons.
The photoperiod is the period of time each day during which an organism receives illumination. In other words, it is the day length. The photoperiod is mainly determined by the sun. For Bearded dragons, the photoperiod affects the day-night-rhythm which has an effect on their growth and is (over time) used to determine the four seasons of the year. Bearded dragons are diurnal animals, meaning they are mainly active during the day. At night they fall asleep, consume no food and their metabolisms drop. Having, for example, longer days allow for more feeding and subsequent growth. This is why baby Bearded dragons that hatch in summer, with longer days, have a greater chance of survival. As the days get shorter and the nights get longer, Bearded dragons are able to determine that winter is approaching and that it is not ideal to breed anymore.
Natural photoperiod for Bearded dragons
When looking at the day-night rhythms in the Australian deserts one will see a clear difference between the daylight length in summer and the daylight length in winter. During the summer, the period between sunrise and sunset will about 14 hours. This gives about 10 hours of night time. In winter the sun will shine for about 12 hours per day. During autumn and spring the daylight length will gradually change towards or away from 14 hours per day. Also see Bearded dragons in the wild for more information.
The pineal gland of Bearded dragons
Most vertebrates, including Bearded dragons, have what is called a pineal gland (also referred to as a ‘third eye‘ or ‘pineal eye‘). It is a small pea-shaped gland situated in the brain which is sensitive to environmental light. The pineal gland of Bearded dragons should not be confused with the Jacobson’s organ (which is an organ used to ‘smell’). Although some of the pineal gland’s functions are still unknown, it is known that it secretes melatonin (a hormone) when lizards are exposed to light (e.g. daylight). Being dependant on the seasonal changes (in other words the photoperiod), the pineal gland of most lizards are well developed.
Longer days (14 hours per day) will lead to more melatonin secretion and vice versa. In other words, when the concentration of melatonin is relatively low (i.e. when the day-length is relatively short when compared with the night-length – about 12 hours per day) a Bearded dragon’s brain can determine that it is winter. Bearded dragons can also determine whether it is spring or autumn through regular changes of melatonin. When there is a sudden change in the concentration from low to high (i.e. during spring) these hormones, among other things, stimulate breeding behaviour.
Controlling the photoperiod for pet Bearded dragons
When keeping Bearded dragons as pets, the photoperiod of the enclosure should be considered. To create a photoperiod that resembles the day-night cycles in the Australian deserts, lighting equipment (heating and UV lighting) can be used. By changing the on-off light cycles in combination with a seasonal roster a more natural photoperiod can be created. This process can either be done manually or by using a programmable electric timer.
As mentioned previously, lighting should be on for 14 hours per day during the three main months of summer. During the three winter months, the lights should be on for 12 hours and off for 12 hours. During the three months of spring, the light period should be gradually increased from 12 to 14 hours per day and from 14 to 12 hours per day during autumn.