Large sack-winged bat

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Large sack-winged bat
Greater sack-winged bat (Saccopteryx bilineata)

Greater sack-winged bat ( Saccopteryx bilineata )

Systematics
Order : Bats (chiroptera)
Family : Smooth-nosed cantails (Emballonuridae)
Subfamily : Emballonurinae
Tribe : Diclidurini
Genre : Sac-winged bats ( Saccopteryx )
Type : Large sack-winged bat
Scientific name
Saccopteryx bilineata
( Temminck , 1838)

The sack-winged bat ( Saccopteryx bilineata ) is a bat from the smooth-nosed cantilever family that is native to Central and South America. It is one of the best-studied Neotropical bat species.

Distribution area of ​​the great sack-winged bat

description

With a total length of 74 mm and a weight of up to 9.3 g, the great sac-winged bat is the largest species of its genus, with the females being heavier than the males (sexual dimorphism ). The coat color of the big sack-winged bat is black to dark brown with two light, wavy stripes on the back that extend from the shoulder over the entire trunk. The abdomen is usually lighter than the fur on the back. The tail fly skin is slightly hairy up to the base of the tail.

The males of the great sac-winged bat have fleshy pockets in their flight membrane, which are filled with a strongly smelling liquid. In the females these pockets are only rudimentary . In adult, sexually mature males, the pouch is flesh-colored, while young males have dark pouches. The sack-winged bat differs from other representatives of its genus in its size, dark fur and the clear color separation of the light stripes from the rest of the fur.

The sack-winged bat is often confused with the nasal bat ( Rhynchonycteris naso ). However, this has no wing pockets and is hairy on the arms. In addition, the snout of the nasal bat is elongated. Bats that hang from tree trunks in a vertical line over rivers and have two stripes on their backs are mostly nose bats and not sack-winged bats .

Close-up of a large sac-winged bat

Way of life

During the day, the big sac-winged bat hangs on vertical, well-lit structures such as buttress roots of large trees, in tree hollows, on the walls of buildings and on bridges. Such hanging places are usually used by the same colony for years. The colonies contain up to 50 animals, which are individually spaced 5 to 8 cm apart.

Like most bats, the great sac-winged bat is nocturnal and feeds exclusively on insects that it catches in flight. She uses echolocation calls in the frequency range from 42 to 58 kHz for orientation. All members of a colony hunt within a defined area that is likely to be defended by the males against intruders from other colonies.

Reproduction

Females can become pregnant a year after birth. In Costa Rica all females come into oestrus simultaneously for 1–2 days in December . Young animals are born after a relatively long gestation period of 169 days on average at the beginning of the rainy season in early June, the period with the highest occurrence of insects. While foraging, the females carry the young around with them. The cubs make their first flight attempts from the age of 2 weeks and are breastfed for up to 12 weeks.

socialsystem

After weaning, the female pups leave the mother colony, while the majority of the males remain in the colony. It is believed that the females leave the colony to avoid inbreeding with their fathers and brothers. The males stay in the colony because it is not the dominant males who are harem owners, but those who have lived in the colony the longest. The males are queuing up to get a territory. Correspondingly, one finds some males defending harems in colonies, while so-called peripheral, younger males can often be found on the edge of the colony. A territory is taken over at an average age of two years. The males remain loyal to their harem all their lives, even if there are no females hanging in their territory or neighboring harems become free.

Harem males show courtship and territorial behavior all year round. The territories within the colony each cover 1–2 m² and up to 8 females. The territories are marked by the males with a scented secretion from glands on the chin. The borders of the territories are also defended with social calls, as well as by so-called "salting" (in German "salting"), a behavior in which the male opens the wing pocket with the wing closed and fans his scent at the opponent. Direct physical confrontations are rarely observed.

Wing pouch of a male sack-winged bat

Courtship behavior

The female great sac-winged bats are physically superior to the males, which is why copulation cannot be forced. The females choose their sex partners. In general, harem males have a higher reproductive success than peripheral males. However, males without a harem also manage to father young animals. In addition, a male cannot secure the complete paternity of the young animals in his harem. The mating system of the great sac-winged bat therefore shows similarities to a leks in which several males within a colony constantly compete for the females. Male sack-winged bats show a complex courtship behavior, which among other things consists of an energetically expensive soaring flight . The male buzzes in front of the female of his harem with open wing pouches. At the same time, the wings are moved in such a way that the scent of the bag is fanned out to the female. Such whirring flights are energy-consuming, since no lift can be generated while fanning and the males have to use a laborious flight maneuver to stay in the same position in the air. The duration of the soaring flight could therefore serve the female as an indication of the general quality of the male.

The scent in the wing pockets is actively mixed by the males. The male cleans the pockets with saliva and urine in the later afternoon. After cleaning the pockets, the males convey secretions from the genital region into the pocket. Together with secretions from the facial glands, the males mix such an individual fragrance, which very likely plays a decisive role in the choice made by the females. Chemical analyzes showed that the smell of adult males is composed of 185 substances. Although the sister species Saccopteryx leptura also uses scent for courtship, its composition differs significantly from that of the great sack-winged bat. Experiments have also shown that the females can actively differentiate between the scent of their own and that of their sister species. It is believed that the scent contains information about the male's health status, for example, on the basis of which the females can make their choice of mate.

Vocalization

In addition to echolocation calls, a large number of social calls are known:

  • Barking (English "Bark"): Are produced in rare physical confrontations and move in the same frequency range as echolocation calls, but are longer.
  • Babble (English "Chatter."): Sequences of up to 50 calls that are likely to have a social function.
  • Pipes (English "Whistle".): Produced by the males during the Schwirrflüge and are located partly in the audible range by humans.
  • Screech (English "Screech".): Frequent calls that are audible to humans and are usually produced in conflicts, such as when an individual fails to comply with the distance from its neighbors.
  • Territorial song (English "Territorial song"): 10–50 calls produced by males, which form a kind of melody that lasts about 1.6 seconds. The last calls are at 6 kHz in the audible range for humans. Territorial chants are very variable and individual. The lower the frequency and the more often the singing, the higher the reproductive success of the singing male.
  • Courtship song (English "courtship song".): Produced by the males at night before territorial singing and the morning after returning to the colony and accumulates in the mating season. One female is sung about each time. The courtship singing is very individual and consists mainly of high trills and up to five overtones , some of which are within the audible range for humans.

The large sac-winged bat thus shows an unusually high repertoire of calls. Studies have shown that young animals likely learn the calls by chattering, similar to humans and some primates.

distribution and habitat

The distribution of the sack-winged bat extends from southern Mexico to Brazil and Bolivia , although they usually do not exceed 500 m above sea level. M. occurs. Thanks to its widespread use, the IUCN classifies its population as safe.

literature

  • FD Yancey, JR Goetz, C. Jones: Saccopteryx bilineata . Mammalian Species, No. 581, 1998, pp. 1-5.
  • JW Bradbury, SL Vehrencamp: Social organization and foraging in Emballonurid bats . Behavioral Ecology and Sociobiology 1-2, 1976.

Web links

Commons : Bag-winged bat ( Saccopteryx bilineata )  - Collection of images, videos and audio files

swell

  1. CC Voigt, F. Schwarzenberger: Reproductive endocrinology of a small tropical bat (female Saccopteryx bilineata; Emballonuridae) monitored by fecal hormone metabolites . Journal of Mammalogy 89, 2008, pp. 50-57.
  2. CC Voigt, O. Behr, B. Caspers, O. von Helversen, M. Knornschild, F. Mayer, M. Nagy: Songs, scents, and senses: Sexual selection in the Greater sac-winged bat, Saccopteryx bilineata . Journal of Mammalogy 89, 2008, pp. 1401-1410.
  3. M. Nagy, Heckel, CC Voigt, F. Mayer: Female-biased dispersal and patrilocal kin groups in a mammal with resource-defense polygyny . Proceedings of the Royal Society B 274, 2007, pp. 3019-3025.
  4. ^ CC Voigt, WJ Streich: Queuing for harem access in colonies of the greater sac-winged bat . Animal Behavior 65, 2003, pp. 149-156.
  5. B. Caspers, G. Wibbelt, CC Voigt: Histological examinations of facial glands in Saccopteryx bilineata (Chiroptera, Emballonuridae), and their potential use in territorial marking . Zoomorphology 128, 2009, pp. 37-43.
  6. G. Heckel, O. von Helversen: Male tactics and reproductive success in the harem polygynous bat Saccopteryx bilineata . Behavioral Ecology 13, 2002, pp. 750-756.
  7. CC Voigt, O. von Helversen: Storage and display of odor by male Saccopteryx bilineata (Chiroptera, Emballonuridae) . Behavioral Ecology and Sociobiology 47, 1999, pp. 29-40.
  8. ^ B. Caspers, FC Schroeder, S. Frank, CC Voigt: Scents of adolescence: The maturation of the olfactory phenotype in a free-ranging mammal . PloS One, 2011.
  9. BA Caspers, FC Schroeder, S. Franke, WJ Streich, CC Voigt: Odor-based species recognition in two sympatric species of sac-winged bats (Saccopteryx bilineata, S-leptura): combining chemical analyzes, behavioral observations and odor preference tests . Behavioral Ecology and Sociobiology 63. 2009, pp. 741-749.
  10. Oliver Behr, Otto von Helversen: Bat serenades - complex courtship songs of the sac-winged bat (Saccopteryx bilineata) . Behavioral Ecology and Sociobiology 56, 2004, pp. 106-115.
  11. M. Knörnschild, O. Behr, O. von Helversen: Babbling behavior in the sac-winged bat (Saccopteryx bilineata) . Natural Sciences 93. 2006, pp. 451–454.
  12. Saccopteryx bilineata in the IUCN Red List of Threatened Species .