Greater Bulldog Bat
(Noctilio leporinus)

(Murcielago Pescador, Fishing Bulldog Bat)

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Order: Chiroptera

Family: Noctilionidae

Genus: Noctilio

Species: Noctilio leporinus

Geographic Range

Noctilo leporinus is found in tropical and subtropical parts of the New World from Southern Vera Cruz (Mexico) to Northern Argentina and Southeastern Brazil. This species is also found on the Greater and Lesser Antilles, and the Bahamas.

Habitat

They roost near streams, coastal marine habitats, major river basins, or other moist places.

Physical Description

Mass
60 to 78 g
(2.11 to 2.75 oz)

Length
98 to 132 mm
(3.86 to 5.2 in)

The sexes are slightly dimorphic in size, the males averaging larger than the females. A male weighing 78 g, and a female weighing 60 g were reported by Klingener, Genoways, and Baker (1978). Head and body length is 98 to 132 mm, and forearm length measures 70 to 92 mm.

The sexes are also dimorphic in color, with males having reddish to orange pelage dorsally, and females generally having greyish or dull brown fur. Both males and females tend to have paler underparts, and the pelage is extremely short.

Noctilionids have a pointed muzzle and lack a nose leaf. The nose is somewhat tubular and projects slightly beyond the lips. Upper lips are smooth but divided by a "hare lip", a vertical fold of skin under the nostrils. The lips are also large and swollen in appearance, suggesting the common name, greater bulldog bat.

This bat presents a formidable dentition. Its cheeks are elastic and can be greatly expanded. Internal cheek pouches are present. The ears are large, slender, pointed, and separate. There is also a tragus which has a serrated margin.

Noctilio leporinus has wings which are long and quite narrow, being more than two and a half times the length of the head and body. Nearly 65% of the wingspan is composed of the third digit.

The tail is more than half as long as the thigh bone. It extends to about the middle of a well-developed uropatagium, or tail membrane. The tail tip is free, protruding for about 10 to 15 mm from the dorsal surface of this membrane. The uropatagium is supported by the legs, tail, and calcar, or heel extension. The calcar is a cartilaginous structure that articulates with the heel bone (calcaneum) and is unique to bats. In this fishing species, the calcar is large and serves to hold the uropatagium out of the water as the bat flies close to the surface.

Noctilio leporinus has unusually long hind limbs and very large hind feet with strong gaff-like claws. Fishing bats tend to have hind feet 1.8 to 3.9 times larger than related non-fishing bats.

Reproduction

Breeding interval
These bats apparently breed once per year.

Breeding season
Pregnancies occur from September until January, although the time of mating is apparently unreported in the literature.

Number of offspring
1 to 1; avg. 1

Gestation period
2 months (average)

Time to independence
1 months (average)

Bachelor males roost apart from females. Males residing with female groups stay for two or more reproductive seasons. Female N. leporinus bear a single young each pregnancy. This appears to form the basis of a polygynous social organization.

This species tends to have pregnancies occuring from September until January, and lactation is first seen in November and continues until April. This is a general pattern, however, and it can vary with geographical location. Reproduction corresponds to seasons of greatest food availability.

Young bats don't leave the roost for their first attempts at sustained flight until nearly adult size. At that time they are slightly less than one month of age and the parents have remained at the roost throughout. This suggests a high degree of bi-parental care which may be a characteristic of this species.

Behavior

Greater bulldog bats roost in caves, rocky crevices, or hollow trees, and only occasionally in human habitations. Large roosts of hundreds of bats have been reported. They may also roost in smaller groups of up to 30 individuals and forage at night in groups of 5 to 15 animals.

Their fishing behavior is of particular interest. They generally feed at dusk and at night, but have been seen in the late afternoon near pelicans, presumably catching small fish disturbed by the pelicans.

Noctilio leporinus fishes over ponds, rivers, and at the edge of ocean surf. Small groups of these bats fly within 20 to 50 cm of the water surface using echolocation to detect fish, by zig-zagging over the water and chirping. This is termed high search flight. When a bat detects a disturbance in the water that may indicate the presence of small fish, it descends to the water surface. In this low search flight, the bat's body is parallel to the water only 4 to 10 cm above it.

The bat then rakes its enormous taloned feet, like two grappling hooks, through the water, trying to gaff fish. If able to impale an unsuspecting victim, the bat raises the fish to its mouth and chews it while still flying. The partially masticated fish is then stored in the cheek pouches. This allows the bat to continue fishing, increasing its foraging efficiency. Alternatively, the hunter may transfer the fish to the uropatagium and take it to a perch to consume it.

These bats catch fish up to 100 mm in length from depths as great as 25 mm below the water surface.

Another behavior to note is that greater bulldog bats have been seen to make very long rakes in areas where they have hunted successfully before. Bats do this even though there is no water surface disturbance at the time. Researchers suggest this is a memory-directed rake, simply dragging a previously productive area.

Noctilio leporinus also adjusts the frequency of its echolocation call to enhance communication. When two noctilionids are on a collision course, one bat "honks" at the other. This allowd them to veer away, and prevents a collision. The honk is produced by dropping the frequency sweep of the echolocation call an extra octave.

Fish-eating, or piscivory, in bats is thought to have evolved from catching floating or swimming insects off the water. Noctilio albiventris, a closely related species, is primarily insectivorous, and has been found to employ echolocation to capture insects from the water surface. Noctillio albiventris also possesses cheek pouches. Further, the dentition of insectivorous bats is already designed to chop through insects with hard, chitinous exoskeletons. There is only a slight modification in the dentition of piscivorous bats to allow them to chew through fibrous flesh, as well as cut through bone.

Food Habits

Noctilio leporinus catches and consumes fish. It is one of about six bat species that regularly eat fish. It will also eat aquatic crustaceans, stinkbugs, crickets, scarab beetles, moths, winged ants, and other insects, but primarily, it is a piscivore (fish-eater).

Animal Foods:
fish; insects; terrestrial non-insect arthropods; aquatic crustaceans.

Economic Importance for Humans: Negative

Groups of Noctilio leporinus may take significant numbers of small fish from hatcheries and aquaculture projects. Methods for blocking echolocation over hatchery ponds can be effective in preventing these losses.

Other Comments

Generally, bats with long narrow wings are rapid, enduring fliers. The flight of greater bulldog bats has been described as rather stiff-winged and not particularly rapid. However, they are powerful. If knocked into the water, this bat can swim using its wings as oars, and it is capable of taking flight from water.

Regarding food habits, one study on the Island of Culebra, Puerto Rico, showed that during the wet season, the bat's diet was predominantly small insects, but during the dry season, pelagic and freshwater fish represented a greater portion of the diet. This indicates the bat has a flexible foraging strategy, allowing it to adjust to local conditions.

The roosts of greater bulldog bats are characterized by a strong musky odor. This odor comes from oily secretions found beneath the wings, in the subaxillary region. Female bats roost in groups that remain together associating with the same individuals and in the same location for years. Females scent mark their heads with the sub-axil secretions of other females. They do this by rubbing their heads under other bats' wings. These secretions have been found to differ between sexes. It has been suggested this scent may communicate information about sexual identity and reproductive condition. It may also allow bats to be recognized by their odor within the roost and while flying.

Males of this species have an unusual pocket-like fold of skin associated with the scrotum. Glands in this pocket also contribute to the obvious musky odor in males.

Another peculiar characteristic is that N. leporinus' sperm is unique among mammalian spermatozoa. The sperm head is extraordinarily large and flat. There is a large acrosome which lies anterior to the nucleus. This acrosome is shaped into a dozen accordion-like folds that run parallel to the long axis of the sperm. Researchers believe these acrosome ridges may strengthen the sperm head during transport.