Bats are mammals with a peculiar life history. Most of them are smaller than 50 g, but they can live more than 30 years in the wild. This pattern is totally ‘outlying’, considering mammal standards (Barclay et al. 2004).
Most bats have only one pup at a time, and breed up to three times a year (Nowak, 1994).  There are a few exceptions, like bats of the genus Lasiurus, which may have twins.

In general, four basic patterns of bat reproductive seasonality have been described in the wild (Fleming et al. 1973):

  1. seasonal monestry: only one reproductive peak a year;

  2. seasonal polyestry: two or three peaks a year;

  3. a long reproductive season with a short break;

  4. continuous reproduction with no distinct seasons.

There are many different mechanisms that occur in bat reproduction. One interesting phenomenon is ‘delayed implantation’. When this delay happens, females mate, fecundation occurs normally, but it takes months for the embryo to be implanted in the uterus and resume development. It is supposed that this mechanism allows females to mate at different seasons, so birth and weaning can occur at the most favorable seasons.