A newborn has a forearm length about 49 mm (1.9 in) and weighs 55 g (1.9 oz).
Its forearm length increases an estimated 0.029±0.005 mm each day, while its weight increases 0.33±0.7 g per day.
This is appreciably slower than other flying foxes.
The thumb does not increase much in size, only 1.2% bigger in adults than juveniles, suggesting the thumb is important in social interactions or moving in trees prior to flight-readiness.
It becomes flight-ready after five or six months when it reaches an estimated forearm length of 112 mm (4.4 in) and weight of 163 g (5.7 oz), respectively 86.3% and 41.2% of their adult dimensions.

Males begin to mature at 15 months of age and are sexually mature by 27 months; females reach physical maturity at 24 months, and sexual maturity by 28 months.
This is one of the oldest ages of maturation of any known bat.
For example, the grey-headed flying fox reaches sexual maturity at 16 and 11 months for males and females respectively.
This may be due to a lack of predators on the island and an overall low natural mortality rate, which would make it more beneficial to delay development in order to prolong lifespan.
Development is mainly skeletal prior to maturation, and then focuses more on weight gain.
A newborn has a forearm length about 49 mm (1.9 in) and weighs 55 g (1.9 oz). Its forearm length increases an estimated 0.029±0.005 mm each day, while its weight increases 0.33±0.7 g per day. This is appreciably slower than other flying foxes. The thumb does not increase much in size, only 1.2% bigger in adults than juveniles, suggesting the thumb is important in social interactions or moving in trees prior to flight-readiness. It becomes flight-ready after five or six months when it reaches an estimated forearm length of 112 mm (4.4 in) and weight of 163 g (5.7 oz), respectively 86.3% and 41.2% of their adult dimensions.
Males begin to mature at 15 months of age and are sexually mature by 27 months; females reach physical maturity at 24 months, and sexual maturity by 28 months. This is one of the oldest ages of maturation of any known bat. For example, the grey-headed flying fox reaches sexual maturity at 16 and 11 months for males and females respectively. This may be due to a lack of predators on the island and an overall low natural mortality rate, which would make it more beneficial to delay development in order to prolong lifespan. Development is mainly skeletal prior to maturation, and then focuses more on weight gain.
Christmas Island flying fox