Reproduction

           Reproduction in pallid bats (Antrozous pallidus) (as well as other species of bats) is centralized around hibernation (Oxberry, 1979). What’s interesting about their reproductive strategies is that it often occurs in two stages: before hibernation and after hibernation (Oxberry, 1979). The female reproductive period starts in autumn (before hibernation) and finishes in the spring (after hibernation).

           There are two different arrangements to the reproductive cycle (Oxberry, 1979). One is when procreation takes place in the late summer or early autumn; hibernation then follows shortly after. In this arrangement, the female reproductive system collects the sperm and saves it until the spring when ovulation occurs. Once ovulation has started, the sperm will then fertilize the egg, resulting in gestation (Oxberry, 1979).

            Another way of reproduction is when procreation, ovulation, and fertilization all occur before the female enters hibernation. Even the beginning stages of the formation of an embryo occur. In other words, the female pallid bat begins hibernation while already being pregnant (Oxberry, 1979). Now you may be wondering if the embryo starts to develop while the mother is in hibernation; the answer is no. What happens is that the embryo is not implanted into the uterus until the spring, where it will then result in gestation after implantation (Oxberry, 1979). So the main theme between both types of reproductive arrangements is the presence of a delay somewhere in the cycle; there is either a delay in ovulation until the spring or there is a delay in implantation until the spring (Oxberry, 1979).

           Why is it advantageous for pallid bats to split-up their reproductive cycle? Reproduction in animals (less so in humans) is all about timing and energy costs. Giving birth in the spring is when environmental conditions are the most supportive for the development of offspring (Crichton and Krutzsch, 2000).  If a female pallid bat had to engage in copulation, ovulation, fertilization, implantation, and gestation all after hibernation, there wouldn’t be enough time to complete all those steps of reproduction and have the brood ready to be delivered in time for spring. Also, keep in mind that procreation is very expensive in terms of energy usage; a female pallid bat just coming out of hibernation is low on energy as it is (Crichton and Krutzsch, 2000). Throwing in complete reproduction would be absolutely unpractical. In conclusion, the most advantageous method of reproduction in pallid bats is to separate the stages into occurring before hibernation and occurring after hibernation (Oxberry, 1979).

           The gestation period for a pallid bat is between 53 and 71 days, and parturition typically occurs between May and June. Pallid bats also have a relatively small litter size: usually one to three young, averaging at two (Weber, 2009). The offspring are generally weaned from their mother at about six to eight weeks of age, and are able to reproduce during their first mating season (Weber, 2009).

           The primary reproductive behavior that has been observed in pallid bats is the use of mating calls. The mating calls in bats are complicated and specialized, therefore they are distinct between each species; a pallid bat will be able to recognize the mating call of a fellow pallid bat (Pfalzer and Kusch, 2003). The purpose of a mating call is to attract a potential suitor. Even though the mating calls may seem simple and universal between species, they are actually highly evolved and selective to ensure the best males from the species mate with the best females from that same species (Pfalzer and Kusch, 2003).

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