Social Spacing:

Vampires are a cross between a home-range and territorial species. They most definitely do not have classical (multipurpose) territories, utilizing instead a home range for feeding and living. Their food source, being other animals, is mobile, forcing the vampire to be the same. Because they switch roosts so often, it would not make sense to defend them permanently. Turner found the range of vampires to be roughly 2 km on either side of a river, which vampires use to navigate, though Schmidt (1988) notes that ranges vary greatly based on local factors such as roost abundance and food availability.

Males do defend small territories within roosts, similar to leks. These territories are mating only though males do not display upon them and they do not touch. Females live in the top of roost trees in groups of 8-12 adults and any dependant offspring (Wilkinson 1985a) and show no territorial behavior other than aggression towards males when they get too close. When roosting in caves (vampire aggregations can reach past 2000 individuals), subgroups of 10-20 females with recent young are identifiable. (Wilkinson 1988).

The roosts themselves could be classified, by our system, as temporary, transient mating-nesting territories, the males supplying the mating territorial aspect and the females using them for shelter and to rear offspring, though they are separated from the males within the roost. This classification is somewhat of a stretch, however, because females, with or without young, do not always roost in a tree with a male, and females themselves do not defend these roosts. Vampire bat social spacing cannot be classified strictly as home range, as it looks at first glance, because they do at times defend territories, even if it is only one sex.

Male Spacing: Males are either solitary or in small bachelor groups; even when there are several males in a tree, they only interact to fight over access to females. Because they are in smaller groupings males occupy more trees than females. Males also move among fewer roosts than females. This can be explained by male territorial behavior; they will remain in a roost and defend their space (against other male vampires) even after females have moved on. There is correlation between the number of males defending spaces in a tree and the amount of time females spend there; the more time the roost is occupied by females, the more males there will be. Resident males, especially the alpha male, will guard the opening of their tree against visitor males, and chases sometimes cover great distances throughout the night. (Wilkinson 1985a).

Female Spacing: As stated earlier, a female group usually contains 8-12 adults plus any dependant offspring. Each group of females is loyal to a set of 2-5 diurnal roosts and splinters off into 2-4 female (with young) subgroups whose composition fluctuates. They switch roosts every few days. (Wilkinson 85a, 88, 90) Thus vampires are a fusion-fission group.

Movement: (Trajano 1996)

Trajano observed small ranges (radius 2-3 km), movement between roosts and within karstic (cave) roosts, long-distance migrations, and equal or higher male movement than female in the common vampire bat (contrary to what Wilkinson found). Wilkinson proposed that male movements between roosts were to gain access to more females, though these would have to be those males without a territory in a female-occupied tree. This discrepancy between the two studies may be due to their different locations, Wilkinson's in Costa Rica and Trajano's in Brazil and their different environments. Those bats in Trajano's studies lived in caves and in generally larger populations than those in Costa Rican tree roosts, which could mean there were less opportunities for males to establish their own territories next to a female group, thus making a higher percentage of males solitary, "intruder" males.

Vampires prefer to move along valleys or riverbeds, most likely aiding in navigation. Trajano noted that cave vampires also show fidelity to a set of roosts and move frequently within that set and describes them as "relatively sedentary" in that they may reside in the same area (not roost) for long periods of time. Wilkinson (1988) found that after 5+ years bats that roosted together in previous studies were still roosting together in the same area.

The one pattern that could be derived from this study of vampire bat movement is in relation to climate. The bats tended to be more spread out during the warmer months, when many small roosts were available. As ambient temperatures decreased, these small caves and trees could not maintain a suitable microclimate for the bats, and they congregated in the larger, more stable caves instead. Lowered food availability during the cooler months may also lead to longer-distance migrations.

Of the caves in Trajano's study, the smallest and most remote had the largest and most stable vampire colony, due to lack of other suitable roosts in the area. It was also located in a region of abundant livestock. These vampires concentrated themselves and remained in the area due to the environmental factors of food and housing, which determine how vampires group themselves.

The environmental factor of predation affects vampire grouping by dictating in part which roosts are suitable; those that permit total darkness even in daylight and thus provide appropriate cover from potential predators

Cohabitants: Vampire bats do not hold exlusive rights on roosts, as other species of bats sometimes reside along side them. Vampires seem to be the dominant species, if such a thing is possible. They always choose the tallest, darkest location within the roost. When they are using it, the number of other bats inhabiting the roost either stays stable or declines, and when the vampires move on, the non-vampire population either remains stable or increases. This suggests the other bats defer to the vampires' presence. (Turner 1975).

Those bat genus' that roost with vampires: Martibeus, Carollia, Glossophaga, Micronycteris, Saccopteryx, and Sturnira.

Dispersion pattern: Passive vs Active benefits:
Animals form non-random aggregations when the benefits of living socially outweigh the costs. The two types of benefits are passive and active. Passive benefits are resources around which the animals aggregate, whereas active benefits are in the form of interaction between the individuals.

Wilkinson ruled out passive benefits such as roost preference (for the tree itself and its microclimate), predator avoidance, and minimizing foraging distance, concluding that adult females form patterns of association through active, individual choices, primarily to facilitate blood sharing.

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

© Copyright 2002 Department of Biology, Davidson College, Davidson, NC 28035 - - - - - - - - - - - - - - - - Last updated: 19 April 2002