mtgsys

The mating system of the common vampire bat is determined by the social structure of the principal colony. The most prevalent type of social structure is a harem with one male (Wilkinson 2001). Within the harem there is one dominant male, called the harem male (Nowak 1991). The harem male is the only male that mates with the females in his harem (Lord 1993). The females in his harem have ample opportunities to mate outside of the harem, but rarely will mate with a male other than the dominant male (Lord 1993). This action by females shows that females can refuse to mate with certain males, because bachelor males attempt to mate with females when possible (Wilkinson 1985b).

Common vampire bats can live in a harem with multiple males (Park 1991). In this group the males have a dominance hierarchy in which the dominant male, the harem male, fathers at least half of the offspring (Wilkinson 2001). The beta male fathers the second most offspring, and the third ranked male fathers the third most (Wilkinson 1985b). The females in harems with multiple males may reject to mate with the harem male (Park 1991). This rejection of certain males may be a means against inbreeding (Park 1991).

The mating system of these bats is classified as resource defense polygyny (Wilkinson 1988; DeNault & McFarlane 1995). The mating system is polygyny because male common vampire bats mate with more than one female (Wilkinson 1985b). Also, the males and females have a moderately strong relationship (DeNault and MacFarlane 1995). The harem male in the principal colony defends the females in the colony from intruding males that try to mate with the females (Wilkinson 1985a, Wilkinson 2001). Male vampire bats may share food with females (DeNault & McFarlane 1995). Lastly, females are reluctant to leave a principal colony for another because vampire bats’ survival relies on the reciprocal altruism that requires long lasting bonds (Wilkinson 1990; Wilkinson 1985b). A female vampire bat that switches colonies may not be incorporated into the social activities of her new colony, such as grooming and food sharing (Wilkinson 1985b). The mating system is specifically resource defense polygyny, because males in a colony will defend their roost after the females have moved to a new one, which refutes female defense polygyny (Wilkinson 1988). Females are not constantly moving so males do not have to defend the females while moving throughout a home range.

Females have an estrous cycle (Turner 1975). When a female is in estrous she release only one egg, although both ovaries are functional (Schmidt 1988). The actual act of mating last one to three minutes (Turner 1975). The male mounts the female from the posterior end (Turner 1975). Then he grasps her back with his teeth and mates (Schmidt 1988). After mating, there is a vaginal plug containing sperm present in the female (Schmidt 1988).

Copulation occurs in the day roost (Wilkinson 1985b). The foraging areas used at night by females and males rarely coincide, and if a male and female interact outside the roost it is usually agonistic in nature (Wilkinson 1985b). The vampire bat uses more energy raising its young than any other bat of similar size (Wilkinson 2001). The care for the young is solely the responsibility of the mother. The common vampire bat has a gestation period of about 205 days (Lord 1992). Female common vampire bats birth one offspring per pregnancy per year usually (Lord 1993; Nowak 1991). The female is receptive to males two months after she gives birth (Wilkinson 1985b). Females can be fertile for up to fifteen years, which is very long given that the oldest known vampire bat was nineteen years old (Tshchapka & Wilkinson 1999; Nowak 1991).

The common vampire bat is reproductively active all year, however there are peaks in conception and birth of offspring in the rainy season (Nowak 191, Lord 1993). This peak is attributed to the elevated humidity that produces more roosts for bats to disperse into (Lord 1993). The more spread out the bats are the more conducive the environment is for conception (Lord 1993). Also, it is believed that vampire bats have coincided the births of their offspring with the births of their prey (Turner 1975). A spike in available prey makes it easier for the mother to gather blood for herself and her offspring, as well as provides the young bats with young prey to practice foraging techniques on (Turner 1975; Delpietro & Russo 2002). Lastly, it is advantageous for the females to give birth near the same time, because when a mother dies another lactating female will feed the orphan pup (Delpietro and Russo 2002). The offspring are fed solely on milk for three months (Lord 1992). After which they are fed a mixture of milk and regurgitated blood from the mother (Lord 1992; Delpietro & Russo 2002). The mother leaves the pup in the roost while she forages (Lord 1993). When she returns she uses vocalizations to find her pup and regurgitate blood to it (Wilkinson 1985a; Lord 1993). On occasion a pup will acquire regurgitated blood from another pup’s mother (Wilkinson 1990).

At birth the young weighs about twenty percent of the weight of its mother, but it will reach adult weight by the end of its first year (Wilkinson 2001). The newborn’s eyes are open and working at birth (Schmidt 1988). It can crawl as soon as it is born (Schmidt 1988). The offspring are able to accompany their mother on hunts at six months, but may not be weaned until around nine months (Lord 1993). The mortality rate of one-year-old bats is 54 percent, which is mostly a result of young bats not being able to successfully bite and acquire blood regularly after they are weaned (Wilkinson 1988).