Proboscis Bat, Phynchonycteris naso

Proboscis Bat, Phynchonycteris naso. Photograph taken in the coastal region of Costa Rica, February 2023. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California.

Rhynchonycteris naso, is a member of the Emballonuridae Family of sac-winged and sheath-tailed bats. The Emballonuridae Family consists of fifty-five species placed into two subfamilies and fourteen genera. There is only one species in the Rhynchonycteris genus. The Proboscis Bat is also referred to as the Brazilian Long-nosed, River, and Sharp-nosed Bat. In Spanish, they are known as Murciélago Narizón.

Poboscis Bats are characterized by their long, fleshy, and pointed noses. They are relatively small with a soft and dense pelage. Their dorsal side is gray-grizzled brown with two faint white stripes that form a distinct hourglass shape on their lower back and rump. Their ventral side is pale brownish gray with a dark brown patagium. Their dark brown ears are prominent and tapered distally at the tip. Tufts of gray fur line their forelimbs. Males and females are similar in appearance and display no significant sexual dimorphism. Body length ranges from 3.7 cm (1.5 inches) to 4.3 cm (1.7 inches) including their tail, which has an individual length of 1.54 cm (0.6 inch) to 1.68 mm 0.7 inch). While most individuals weigh approximately 4 g (0.14 oz), pregnant females can weigh up to 6 g (0.21 oz). Their average wingspan is approximately 2.4 cm (0.9 inch).

Proboscis Bats are a social and primarily nocturnal species. Colonies can include anywhere from three to forty-five individuals, although colonies of five to eleven individuals are more commonly observed. Some colonies can reach up to one hundred members in size. Each colony has between three and six different roosting sites. When disturbed, individuals will travel in a linear formation between sites. A roosting site can include both sexes, however, females tend to be separated according to their reproductive state. These bats roost approximately 20 m (66 feet) to 100 m (328 feet) away from other individuals. Smaller groups tend to be found roosting in a linear pattern along a tree. In larger groups, they often roost in an oval pattern or segregate into smaller groups. This species roosts in the open and sometimes flies during the daytime.

Proboscis Bats are polygynous and although the male to female ratio is typically equal, breeding females mainly copulate with 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. It is believed that dominant males 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 and more observations must be made to understand this process. Breeding Proboscis Bats can be found throughout the year in different parts of their distribution. However, many individuals cease breeding during the dry season. This is November to March in Costa Rica and April to September in southeastern Brazil. While females produce only one offspring per pregnancy, they may have up to two pregnancies annually and can therefore be polyestrous. Offspring are quite large at birth and can reach adult size within two weeks. Young that are attached for nursing cling onto the mother while she flies, which can disrupt the mothers’ ability to fly, especially with larger young. Within one week of birth young bats begin to venture away from their mother, but they do not stray far. While their 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. Weaning occurs after two to four months, at which time the young bats disperse to nearby colonies. Females undergo their first parturition around eighteen months of age and usually roost with the main colony. However, some have been found in hollow logs, which are thought to minimize the risk of young bats falling into the water. Aside from the general protection of the colony offered by the dominant male, there have been no records of parental care in this species. While no lifespan record of this species has been found, their close relative the Greater Sac-Winged Bat (Saccopteryx bilineata) can live up to six years in the wild.

Proboscis Bats begin foraging at late dusk, typically within 3 m (10 feet) of a water surface with moderate flow and shallow depth either in forests, forest edges, or open areas surrounded by vegetation. While they circle above water to capture their prey, the bats do not typically touch the water’s surface. Colonies actively defend annual foraging locations from other neighboring colonies. Foraging sites are divided into different sections. Reproductive females and their young exploit the prey-rich area in the center, while non-dominant males and non-reproductive females individually forage in the periphery. In the center of a site, as many as six bats have been found in a diameter of 4 m (13 feet) to 5 m (16 feet), flying within 1 m (3 feet) of each other. In contrast, the foraging area used by non-dominant males and non-reproductive females may be as large as 30 m (98 feet) by 30 m (98 feet) in size. As nocturnal aerial insectivores, Proboscis Bats heavily rely on echolocation for prey detection. Their calls include a combination of high intensity signals with sounds that perform certain functions. Narrowband (constant frequency) sounds gather information about small insect prey. Broadband (frequency-modulated) sounds provide details about the bat’s position relative to its surroundings. Most calls are short to prevent the overlap of outgoing and returning echoes from obstacles and/or prey. The diet of Proboscis Bats consists exclusively of insects. While they primarily consume midges and mosquitoes, they are also known to consume some beetles and caddisflies. Common predators of this species include various species of hawks, falcons, and egrets. There have also been documented cases of predation by orb-weaving spiders and northern annulated tree boas. Proboscis Bats can be very difficult to detect when motionless due to their pelage pattern, enabling them to remain cryptic and avoid predators.

Bats that are similar and closely related species 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 are a darker shade of brown and lack the gray-grizzled pattern found in Proboscis Bats. Additionally, male Proboscis Bats lack wing sacs, which are organs on the patagium membrane of the wings that store secretions used for mating rituals and are very prominent in Greater and Lesser Sac-Winged Bats.

From a conservation perspective, the Proboscis Bat is currently considered to be of Least Concern due to their wide distribution and abundance near areas with water. No major threats have been identified for this species. However, they may face some issues associated with the bodies of water nearby their roosts, from which they obtain prey.