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Eidolon helvumstraw-colored fruit bat

By Kia Ruiz

Geographic Range

Eidolon helvum is the most widely distributed African fruit bat. It occurs in most of the subsaharan African continent in forest and savannah zones, the southwestern Arabian penninsula, and Madagascar. A good portion of southern Africa south of Zambia, Malawi, and Mozambique is used for migration purposes. (Smithers, Reay H.N., 1983)

Habitat

These bats occupy a wide range of habitats, from coastal forests to dry, arid regions are used during the year. Prime habitat is tropical forests because of the abundance of food. Straw-colored fruit bats are found at elevations from sea level to 2000 m. These animals typically roost in tall trees, but have also been found in caves. There is great interaction with human communities as well. (Nowak, Ronald M., 1997; Smithers, Reay H.N., 1983)

  • Range elevation
    sea level to 2000 m
    to 6561.68 ft

Physical Description

E. helvum is not entirely straw-colored as its common name would suggest. The neck and back display this signature color while the ventral side of the body is a duller color of brown or grey.

This is one of the larger species of fruit bats. The males are slightly larger than the females. The head and body length is reported to be between 143 and 215 mm. Weights range between 230 and 350 g.

The wings are large and narrow, allowing the bat to fly long distances and not expend as much energy trying to flap them a lot. The wingspan can reach as much as 762 mm.

The head is large and pointed with large eyes and no white facial markings. (Happold, 1987)

  • Sexual Dimorphism
  • male larger
  • Range mass
    230 to 350 g
    8.11 to 12.33 oz
  • Range length
    143 to 215 mm
    5.63 to 8.46 in
  • Range wingspan
    762 (high) mm
    30.00 (high) in

Development

The young are the result of delayed implantation. The embryonic development is 4 months before partrution with a birth weight of 45-50 grams. (Nowak, 1997)

Reproduction

Information on the mating system of these animals is lacking.

Mating occurs in colonies from April to June. The reproductive cycle responds to rainfall, and allows weaning of young to proceed at the time of greatest food availability.

Pairs breed when the dry season begins. There is a delay in the implantation of the embryo in most, but not all, populations. The gestation period typically lasts 9 months, but the embryo only takes 4 months to develop. In populations without delayed implantation, births occur just 4 months after mating.

The young are born in February and March. Females give birth to a single offspring that weighs 50 grams at birth. (Nowak, Ronald M., 1997)

  • Breeding interval
    These animals breed annually.
  • Breeding season
    These bats breed from April to June
  • Range number of offspring
    1 to 2
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    9 months
  • Average gestation period
    275 days
    AnAge

The straw-colored fruit bat has female parental care, like all other mammals. The female nurses her offspring until it is ready to forage on its own. In this species, young are not able to fly at birth,and so are considered altricial. Although females give birth to their young in large colonies, there are no reports of cooperative care of young, nor of paternal involvement in care of offspring.

  • Parental Investment
  • altricial
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

Lifespan/Longevity

Fifteen years is the expected life span of E. helvum. Some individuals do make it to their early twenties, and one individual is reported to have reached 21 years and ten months of age. (Nowak, Ronald M., 1997; Smithers, Reay H.N., 1983)

Behavior

E. helvum is a gregarious, socially roosting species. Even though straw-colored fruit bats feed at night, they are active during the day while resting as they move about the roost. At night the colony leaves the roost in small groups to find food, which is usually in nearby forests or plantations. The diet is primarily frugivorous, although the fruit itself is not eated. Instead, these animals suck the fruit juice from the pulp, then spit the pulp out.

These bats fly in straight lines and at higher altitudes than other species of fruit bats.

The foraging range for a colony is 30 kilometers, as suggested by the typical distance between roosts. Roosts are rarely closer together than 60 kilometers.

Colonies of E. helvum can be large, with groups in migration routes reaching the half-million mark. However, most colonies are not this large. Studies have shown that colonies usually range in size between 100,000 and 1,000,000.

These bats use the same food sources from season to season. Migration occurs when food sources become low enough. The colonies do not break up into smaller sub-colonies when food scarcity happens.

One odd behavior exhibited by these bats is the chewing of soft wood. Apparently, the wood is munched up to obtain water. (Happold, D.C.D., 1987; Nowak, Ronald M., 1997)

Home Range

These bats typically forage over distances of about 30km. (Nowak, Ronald M., 1997)

Communication and Perception

Little information on communication in this species could be found. However, these animals are reported to be quite noisy. In addition to being loud eaters, they apparently chatter to one another in their roosts, indicating that some form of acoustic commmunication is employed. Because they roost in such large groups, it is likely that individuals come into physical contact frequently, and so probably use some sort of tactile communication as well. (Nowak, Ronald M., 1997)

Food Habits

E. helvum is frugivorous. Food is can be consumed while hanging by the phalanges of the feet. The food is eaten noisily. The juices are ingested and the fibrous material is discarded. In addition to consuming fruit juices, these animals are reported to chew up wood and bark, apparently to obtain moisture.

Foods eaten include: Borassus spp., dates, baobab flowers, Adansonia digitata, Bombax spp., Erythrina spp., mangoes, pawpaws, avocado pears, figs, passion fruit, custard apples and loquats. (Nowak, Ronald M., 1997; Smithers, Reay H.N., 1983)

  • Plant Foods
  • wood, bark, or stems
  • fruit

Predation

Little information is available on species which prey upon these bats. Suspected predators include owls, eagles, snakes, buzzards, and civets. Humans are know to consume E. helvum in Zaire and West Africa. (Happold, D.C.D., 1987)

Ecosystem Roles

Because these bats visit flowers, they play a role in pollination. They also serve as agents in seed dispersal. (Mutere, 1980)

  • Ecosystem Impact
  • disperses seeds
  • pollinates

Economic Importance for Humans: Positive

E. helvum are an important diet item for humans in some areas. Straw-colored fruit bats are also important pollinating agents for economically important trees in families Moracea and Bombacear. (Mutere, 1980; Nowak, Ronald M., 1997)

  • Positive Impacts
  • food
  • pollinates crops

Economic Importance for Humans: Negative

Agriculture is greatly affected by E. helvum because these bats live in large colonies that roost near their food source. They can feed heavily in plantations. It is difficult to assess the relative utility of the species as a polinator, versus its negative impact as a crop pest. (Nowak, Ronald M., 1997)

  • Negative Impacts
  • crop pest

Conservation Status

This is a very abundant and common species that has no legal protection.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Kia Ruiz (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

internal fertilization

fertilization takes place within the female's body

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Happold, D.C.D., 1987. The Mammals of Nigeria. New York: Oxford University Press.

Mutere, F. 1980. Eidolon Helvum Revisited. Pp. 145-150 in D Wilson, A Gardner, eds. Proceedings Fifth International Bat Research Conference. Lubbock, Texas, U.S.A.: Texas Tech Press.

Nowak, Ronald M., 1997. "Straw-colored fruit bat" (On-line). Walker's Mammals of the World Online, Version 5.1. Accessed November 25, 2003 at http://www.press.jhu.edu/books/walkers_mammals_of_the_world/chiroptera/chiroptera.pteropodidae.eidolon.html.

Smithers, Reay H.N., 1983. The Mammals of the Southern African Subregion. Pretoria: University of Pretoria Press.

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