This is a collection of lists of mammal gestation period estimated by experts in their fields.
In some cases, some mammal species may have similar gestation periods despite having significantly different body masses.
[22] In response to the conditions of the environment, some mammals, such as bat delay the implantation due to the cold temperature in winter.
[23] Another factor is due to the shortage of food stocks during winter as the insects are being driven away and as the result, bat hibernate in pregnant condition.
[24] In pinnipeds, the purpose of delayed implantation is in order to increase survival chance of the young animals as the mother ensure that the neonates are born at an optimal season.