Rhynchonycteris naso

Geographic Range

Proboscis bats ( Rhynchonycteris naso ) can be found from Veracruz and Oaxaca in southeastern Mexico, down through Central America and reaching the northern half of South America including southeastern Brazil, Peru and northern Bolivia.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Proboscis bats prefer tropical lowlands with an elevation of less than 300 m and are almost always found near or over moving water, but rarely near fast-moving water. Unlike most nocturnal bats, light does not seem to disturb the colony, individuals roost in well-lit areas, usually around 1.8 meters (6 feet) above water. These bats are known to cling upside down in a vertical line on the bark and roots of trees overhanging water, but on occasion, some have been found under bridges, in cave mouths overhanging water, under large curled leaves, such as those of banana plants and under large fabric umbrellas of outdoor Brazilian restaurants.

• Habitat Regions
• tropical tropical

• Terrestrial Biomes
• rainforest rainforest

Physical Description

Proboscis bats are very small members of family Emballonuridae with gray-grizzled brown dorsal sides and two faint white stripes forming a distinct hourglass shape on their lower back and rump. Their ventral sides are pale brownish gray and their pelage is soft and dense, with a dark brown patagium. Their dark brown ears are prominent and tapered distally, much like their tragus. Young bats are slightly darker in color than adults. There is no significant sexual dimorphism, males and females are similar in appearance. Their body mass ranges from 3.8 to 3.9 g, their body length ranges from 37 to 43 mm including their tail, which has an individual length of 15.4 to 16.8 mm. When pregnant, females can weigh up to 6 g. Their average wingspan is 23.9 mm, and their wing aspect ratio (6.54) and wing loading (0.045) are considered intermediate when compared with 25 Neotropical species representing several families. The baculum of male proboscis bats is considerably larger than that of 6 other emballonurid species. Their dental formula is i 1/3, c 1/1, p 2/2, m 3/3 = 32 teeth. Their upper incisors are minute and distinctly separated, while the first upper premolar is relatively large, somewhat triangular in occlusal view and closer to the canine than to the last premolar. Skull lengths range from 11.4 to 12 mm in males and 11.6 to 12 mm in females. Some distinct features of this species include a deep basisphenoid pit and nearly parallel maxillary toothrows. The postorbital process and auditory bullae are well-developed. Similar and closely related emballonurids with overlapping ranges include greater sac-winged bats ( Saccopteryx bilineata ) and lesser sac-winged bats ( Saccopteryx leptura ). Proboscis bats can be distinguished from these species by their elongated muzzle and evenly-spaced tufts of white to pale gray fur along their forearms. The dorsal side of greater and lesser sac-winged bats is a darker shade of brown and lacks the gray-grizzled pattern found in proboscis bats. Male proboscis bats also lack wing sacs, which are organs on the propatagial membrane of the wings that store secretions used for mating rituals and are very prominent in greater and lesser sac-winged bats .

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

Proboscis bats are polygynous and although the male to female ratio is usually equal, breeding females mainly copulate with dominant males. The rest of the colony likely follows a hierarchy, where reproductive females rank higher than non-reproductive females and non-dominant males. Dominant males forage at the edge of the feeding area and protect their colony from neighboring conspecifics using aerial attacks and audible vocalizations. Dominant males are thought to exhibit female-defense over resource-defense, since the males follow the females as they forage, even when they return to their roosting sites at night. Mating in proboscis bats is not well-studied, but during an observed copulation, two males approached a female from opposite sides, leading to what appeared to be inaudible vocalizations by the female. One male proceeded to edge over the female’s body and appeared to vocalize inaudibly, followed by copulation. The female and the second male then took off and executed a downward spiraling flight, until nearly reaching the water surface. However, the purpose of this act is not yet known.

• Mating System
• polygynous polygynous

Throughout the year, breeding proboscis bats can be found in different parts of their distribution, but may cease breeding during the dry season, which is November to March in Costa Rica and April to September in southeastern Brazil. Females produce only one offspring per pregnancy, but may have up to two pregnancies annually and can therefore be polyestrus. Offspring are quite large at birth and can reach adult size within 2 weeks. Weaning occurs after 2 to 4 months, after which, the young bats disperse to nearby colonies. Females undergo their first parturition around 18 months of age. Overlap between lactation with the first young and gestation of a second offspring has been documented.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual

Within one week of birth, young bats begin to venture away from their mother, but do not stray far. While the mothers are out foraging, young bats practice flying at the roost. Once the young are able to fly, they forage along with the breeding females in the central feeding area, until dispersal at 2 to 4 months old. Usually, females with offspring roost with the main colony, but some have been found in hollow logs, which are thought to minimize the risk of young bats falling into water. Aside from the general protection of the colony offered by the dominant male, there has been no record of paternal care in this species.

• Parental Investment
• precocial precocial
• female parental care female parental care
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

The calculated annual survival rate of adult females is at least 79%, but no lifespan record of this species has been found. However, their close relative, greater sac-winged bats ( Saccopteryx bilineata ) can live up to 6 years in the wild. A study of the factors affecting longevity showed that lifespan tends to increase with body mass, hibernation and cave use, but is negatively impacted by increased reproductive rates. Out of 64 species of bats, Saccopteryx bilineata is the most similar to proboscis bats, neither of these bats hibernate or roost in caves frequently; however, they both have a similar body mass and a similar number of offspring annually.

Behavior

Proboscis bats are a social, mainly nocturnal species. Colonies frequently include anywhere from 3 to 45 individuals. Colonies comprised of 100 bats have been observed, although colonies of 5 to 11 are more commonly seen. Each colony has between 3 and 6 different roosting sites. Individuals will travel in a linear formation between sites when disturbed. Offspring that are attached for nursing cling on while the mothers fly, which can disrupt the mothers’ ability to fly, especially with larger young. A roosting site can include both sexes, although females tend to be separated according to their reproductive state. These bats roost 20 to 100 mm away from other individuals. In smaller groups, they can be found roosting in a linear pattern along the tree, but in larger groups, they often roost in an oval pattern, or may segregate into smaller groups. This species roosts in the open and sometimes flies during the daytime. Foraging usually begins at late dusk, and in southeastern Brazil, 30 to 40% of the colonies returned to the roosts after approximately 80 minutes. At around 4 am, bats presently at the roosts, depart for a second foraging and returned after about an hour. Foraging occurs mostly within 3 m of a water surface with moderate flow and shallow depth, either in forests, forest edges, or open areas surrounded by vegetation. The bats circle above water to capture prey, but do not usually touch the water surface. Aided by high maneuverability in flight, proboscis bats are difficult to capture with mist nets since their light body mass does not easily entangle. Colonies actively defend annual foraging ranges from other colonies. Foraging sites are divided into different sections; reproductive females and their young exploit the prey-rich center, while non-dominant males and non-reproductive females individually forage in the periphery. In the center of the site, as many as 6 bats have been found per 4 to 5 m diameter area and may fly within 1 m of each other. In contrast, the foraging area utilized by younger non-dominant males and non-reproductive females may be as large as 30x30 m in size.

• Key Behaviors
• flies
• nocturnal nocturnal
• motile motile
• territorial territorial
• social social
• colonial colonial
• dominance hierarchies dominance hierarchies

Home Range

Proboscis bats have large home ranges used for foraging and multiple roosting sites. A 10-month study on 3 different colonies in La Pacifica, Costa Rica, showed a range of 0.9 to 1.2 hectares, with an average of 1.1 hectares. The distance between each roosting site ranges from 25 to 180 m with some rotation of sites; each site is typically used for 4 to 6 weeks.

Communication and Perception

As nocturnal aerial insectivores, proboscis bats rely heavily on echolocation for prey detection. Their calls include a combination of high intensity signals, with narrowband (constant frequency) and broadband (frequency-modulated) components, of which, the former postulates details about small insect prey, while the latter provides information regarding the bat’s position relative to its surrounding. Proboscis bats emit high frequency calls of approximately 100 kHz, as well as lower frequencies around 47 kHz. High frequency calls indicate short-range detection of small prey in cluttered habitats, while lower frequencies increase the detection range, although only larger prey are perceived. Most calls are short, to prevent the overlap of outgoing and returning echoes from obstacles and/or prey. Complex social signals have not been observed in this species, although vocalizations by both sexes were observed when interacting with intra- and inter-colony newcomers.

• Communication Channels
• acoustic acoustic

• Perception Channels
• tactile tactile
• echolocation echolocation
• chemical chemical

Food Habits

The diet of proboscis bats consists exclusively of insects, mainly those from order Diptera , such as midges and mosquitoes , although some beetles (order Coleoptera ) and caddis flies (order Trichoptera ) have also been found in stomach content analyses. Since Diptera , Coleoptera , and Trichoptera are thought to comprise approximately 87 to 90% of aerial insects found over water, a study has suggested that this species feeds on the most abundant insects in its foraging area.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• insects

Predation

Common predators of proboscis bats include various species of hawks , falcons , and egrets , although there have been documented cases of predation by orb-weaving spiders and northern annulated tree boas . This species can be very hard to detect when motionless, due to its pelage pattern, enabling it to remain cryptic to avoid predators. It also exhibits a cryptic behavioral adaptation where periods of synchronous gentle rocking can be observed throughout the day by most, if not all members of the colony in the absence of any threat. This behavior may also be more likely to occur during gusts of wind and with the combination of synchronous grooming and urination. Since this species tends to roost in open areas and is visually exposed, this behavior may benefit the colony by hiding its movements from potential predators.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

There has been no specific study on the role this species plays on the ecosystem, but due to its diet and large population numbers, proboscis bats may contribute to the control of insect populations in its habitat. In Panama, where these bats occur, research has shown that insectivorous bats indirectly affect herbivory on plants, by reducing herbivorous arthropod abundance. Proboscis bats are hosts to two known internal parasites: a coccidian parasite, Eimeria rhynchonycteridis , and a trypanosome, Trypanosoma cruzi . Some ectoparasites previously found on these bats include polyctenid hemipterans , Hesperoctenes fumarius , three species of streblid batflies: Strebla hirsutus , Trichobius caecus , and T. longipes ; and two species of acarine mites: Eutrombicula variabilis and Periglischrus iheringi . However, the precise effects of these parasites have yet to be documented.

Economic Importance for Humans: Positive

There are no known positive effects of proboscis bats on humans, although in general, insectivores may aid in controlling insect populations.

Economic Importance for Humans: Negative

Proboscis bats can be infected with Trypanosoma cruzi , the parasite that causes Chagas Disease in humans. Although this parasite cannot be directly transmitted from bats to humans without incubation within an intermediate host, the bats can serve as a reservoir host for the development of more parasites.

• Negative Impacts
• injures humans
  • carries human disease

Conservation Status

According to the IUCN Redlist, Rhynchonycteris naso is considered a species of least concern.

Additional Links

Encyclopedia of Life

Contributors

Stephanie Hans (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Leila Siciliano Martina (editor), Texas State University.

References

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