Social Relationships of Desmodus rotundus
The magnitude of females is so great that males cannot defend a harem, or group of females to mate with.  Additionally, males cannot  economically defend a feeding territory because of the superabundance of food.  These two factors  result in males defending a mating territory in which they mate with any females that enter.  Thus, the vampire bat has a promiscuous mating system.  Wilkinson has described the bat mating system as a group of males (from 2-10) establishing residence nearby a group of females (usually ranging from 8-12).  These males fight over the females and fight to roost near the larger groups of females.  Interestingly, the male vampire bats do demonstrate a type of dominance structure.  The dominant male will breed more often than the subordinant males (McCracken 2000). However, females will mate with subordinant males as well and have the ultimate decision in who they will mate with (McCracken 2000).  Thus, female vampire bats can choose a mate based on the He-man strategy.  That is, she will choose which ever male appears to be the best specimen.  After mating, the females leave and groom themselves.    This mating system evolved because the males cannot easily defend either resources or females.  Therefore, their only option is to defend an area of the roost where they know females will be and thus establish a sort of lekking territory.
  The male/male relationships are aggressive for the most part, and there is a dominance.  This is maintained through flapping of wings, biting, and posturing (Greenhall and Schmidt 1971).  The more dominant male mates more often and thus it is natural that the males will be aggressive towards each other in order to obtain more females.  There are no social bonds between males, with most studies citing the male as being more solitary.  Wilkinson's observation that males are often in small groups of 2-10 is most likely because the subordinant males were not able to establish their own territory and so come to stay in the territory of a more dominant male.  This is advantageous because they will get opportunities to mate with the females without actually establishing a territory of their own.  The bonds between the females are very strong.  They are not as critical in explaining the mating system as they are in the social system.  The female groups are very close and they are the centerpiece for the altruistic behavior of the vampire bat.  The food sharing occurs within the female groups.  Food sharing does not occur between vampire bats that have not had a social interaction together and thus have no bond.  For more information please click here to read about reciprocal altruism.  There is no competition between the female vampire bats, and it has no effect on the social system.  The male competition will only affect which males will be successful in establishing a territory.
  Individual bats show various types of aggression while feeding.  It has been observed that while feeding, vampire bats do exhibit a type of physical territoriality.  In one study by Greenhall and Schmidt, it was observed that during a feeding bout there would be some vampires feeding solitarily from a wound,  others feeding one after the other, but not at the same time, and finally multiple vampire bats trying to all feed from the same wound at the same time "crowding, jostling, fighting, and screaming" at each other (Greenhall and Schmidt 1971).  This indicates that there is a type of social hierarchy that contains dominant and submissive relationships (Greenhall and Schmidt 1971).  The study did not mention whether or not they had been able to determine the sexes of these bats that were feeding.
  The gestation period is 6-8 months and once the offspring is born, the female is the sole care-taker (Turner 1975).  Females have one offspring at a time (Dalquest 1955).  The female vampire bat nurses her young on milk alone during the first month.  After the first month, the offspring feeds on regurgitated blood meals until five to six months of age.  At this time the young will accompany the mother during feedings (Mulheisen and Anderson 1994).  Once the offspring reaches maturity (approximately ten months of age) the males disperse and form temporary bachelor groups before attempting to establish their own mating territories.  The female offspring are recruited by the mother to remain in her social group.  Thus, the mother makes a relatively large investment in her young while they are reaching maturity.  Once the female has reached maturity, the mother tries to keep her within her group, most likely because should the daughter stay, the mother is almost definitely assured a group member that will be very willing to participate in reciprocal altruism.
 
  • Habitat and habitat utilization
  • General description of Desmodus rotundus and its social system
  • Social spacing
  • Social cooperation/altruism
  • Summary
  • Bibliography

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