Mating system:

Hierarchical promiscuity: no bonds are formed between males and females (with the exception of parent-young bonds present until juvenile males disperse, and even that is weaker than the mother-daughter bond), not even for the duration of the mating attempt. Females are able to take care of the young on their own and don't need the help of male parental care. Any aid they might need, a result of a missed blood meal, is provided by the other adult females. Females also don't need male protection, as they occupy the safest (highest and darkest) part of the roost and avoid predators rather than fighting them.

Multiple males associate near the females (not directly with them: see Wilkinson diagram) and compete for mating rights on the basis of their linear dominance hierarchy. There are some similarities to lek promiscuity, due to the males defending small, mating only territories within the roosts (if there are more than one male present), with an obvious dominant spot (at the top of the tree: see Wilkinson diagram). However, unlike the key to Lek promiscuity, vampire males do not display for the females; females are not attracted to the males and are often aggressive towards them. Males defend the resource (their territory) and not the females themselves, and continue to guard it after females have moved on. Females are loyal not to males but each other and to a set of roosts, and therefore are exposed to different males (Wilkinson 85a, b, 90).

Because they do not stay with the male and do not need male help or protection, vampires cannot be classified as having resource-defense polygyny: females can easily provide for their and their offspring's own food, shelter, and predator protection.

Males guard the opening of their roost at night from invading males, who will fight viciously for the top spot. Mean top-male tenure is 17 months, and though top males gain most of the copulations (80% of those observed) due to their proximity, maximum paternity rate is only 46%. Females mate readily with males other than the alpha, one having been observed mating with the lowest male on one day and the alpha the next. They also reject the alpha at times or accept a visiting male (at night, whereas most copulations take place during the day). (Wilkinson 1985b, 1988)

Park found, in a captive colony, that females will leave the group when in estrous to avoid the alpha male, most likely to avoid inbreeding. Wilkinson noted that top males tend to have lower maximum paternity levels in their second year of tenure and labeled vampire bat mating as "effectively random" as far as producing genetic heterogeneity within a population. A male does not necessarily need a territory to mate, but his chance will be higher if he does, especially if it is the top one. (Park 1991, Wilkinson 1985b)

~Birth weight (5-7 g) doubles every 20-25 days for about 3 months.

~Adult measurements are reached at 5 months, adult weight at 10. Feet are the same size as at birth.

~Vampires are dependent for a long time compared to other bats. They cling almost constantly at the nipple for 20-30 days and the female will carry them up to age 2 months if they're disturbed.

~At 2 months juveniles begin to acquire flight ability and at 4 months can accompany their mothers on flights to prey.

~Juveniles feed on regurgitated blood in 2nd month (Wilkinson says third) and feed on blood at the prey at 4 but are not weaned until 9-10 mo. They are sometimes fed by other colony members (which goes against Wilkinson observations that only mothers nursed their young). U. Schmidt has observed an orphaned juvenile adopted by an unrelated female.

~Vampires are sexually mature at about 12 months, with no age discrepancy between males and females. Females give birth for the first time at about 17-20 months.

The most critical period: nutritional change between milk and blood. In the wild Wilkinson observed mothers feeding blood to their infants minutes after birth, perhaps to inoculate the digestive tract with the right bacteria, easing the future transition period.

Dispersal: Females are recruited into their natal groups and will join unless their mother dies or moves.
Males disperse, sometimes due to force by adult males, between 12-18 months in the wild (usually at least 3 km away from their natal roost) (Wilkinson 1985a,b, 1988) and at 20-27 months in captivity (Park 1991), facilitating genetic heterogeneity between and within populations.

Parental care, exhibited almost exclusively by female vampires, consists of grooming, nursing and regurgitating, leading young to prey, and at times feeding simultaneously from the wound. (Wilkinson 85a,b, 86)

Mating: Occurs in diurnal roosts at no particular time of day. It is preceded by male erection. He then climbs onto her back and holds folded wings against her body "securely," then grips her abdominal region while grasping the nape of her neck with his teeth. Copulations last about 3-4 minutes (or 1-3 according to C. Schmidt). Male pelvic thrusts are observed, but no audible vocalizations. At the end, the male releases his grips and the female "darts off and begins to groom herself" (Turner 1975). There is no male aggression during copulations, only before. This could be due to the fact that other males often fail to observe the mating, which is usually separated from the colony by 3+ meters. Females, which are larger than males, have the choice in this system. They can fend off unwanted advances by lunging with exposed canines, fighting, or escaping out of reach. They can also switch roosts sites and thus the males tied to them. (Wilkinson 1985b, 1988).

Female estrous cycle: Females can breed year round; there is no defined, synchronous, birthing season, although Turner found a peak in births during the rainy season, when food was easier to come by. Gestation lasts 7 months, with an average birth cycle of about 10 months. About 80% of females become pregnant again within the 2 months following birth. A postpartum estrous has also been observed, so that females are pregnant yet still lactating (Turner 1975). Females must reproduce this often because they only have one offspring at a time and infant mortality rate is about 54%(Wilkinson 85b)

Please note this is an undergraduate website created for Animal Behavior 323 at Davidson, College, NC, by Julie Perry. Questions, comments, suggestions, corrections: please email Juperry@davidson.edu

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