The greater bulldog bat or fisherman bat (Noctilio leporinus) is a type of fishing bat native to Latin America. The bat uses echolocation to detect water ripples made by the fish upon which they prey, then use the pouch between its legs to scoop the fish and its sharp claws to catch and cling to it. It is not to be confused with the Lesser Bulldog Bat, which, though belonging to the same genus, merely catches water insects, such as water striders and water beetles.

It emits echolocation sounds through the mouth like Myotis daubentoni, but the sounds are quite different, containing a long constant frequency part around 55 kHz, which is an unusually high frequency for a bat this large.

General description

The greater bulldog bat is a large bat, often with combined body and head length of 1.9 to 12.7 cm (4.6 to 5 in). It generally weighs from 50–90 grams. ^[2] Males tend to be larger than females, with the former averaging 67 grams and the latter averaging 56 grams.^[3] They also differ in fur color. Males have bright orange fur on the back while females are dull gray.^[4] However, both sexes have pale undersides and a pale mid-dorsal line.^[4] The bulldog bat has tubular nostrils that open forward and down. It has slender, long pointed ear with a tragus with a notched outer edge. The bulldog bat has smooth lips but its upper lip is divided by a fold of skin while its bottom lip has a wart under which are semicircular folds of skin that extend to the chin.^[4] It is these features give bulldog bat gets its name as it resembles a bulldog.

The bulldog bat has a wingspan of 1 meter (3 feet). The wing of the bat is more than two and a half times the length of the head and body with nearly 65% of its wingspan being its third digit.^[5] Its wings are long and narrow and flies in a stiff-winged fashion. The bat’s wing beat is slow and deliberate. ^[5] Like most bats, the bulldog bat has a positive allometric relationship for flight musculature and body mass.^[6] The bat is a capable swimmer and will use its wing like an oar.^[4] The Greater Bulldog bat also has well-developed cheek pouches are used for storing food when foraging, particularly fish. ^[5] Its hind legs and feet are particularly large.^[4]

Distribution and variation

The greater bulldog bat ranges from western (Sinaloa) and eastern (Veracruz) Mexico southward to northern Argentina. It also lives on most Caribbean islands. ^[5] While vast, it’s range is also discontinuous as the bat is restricted to mostly non-arid lowland and coastal areas and major river basin like the Amazon and Parana. There is geographical variation in the species and are classified as subspecies. In the rim of the Caribbean Basin, the bats are large in size and, although variable in color, usually have a distinct but pale mid-dorsal stripe.^[7] These bats are known as N. l. mastivus. In Guianas and the Amazon Basin, the bats are small in size, dark in color, and often without a pale mid-dorsal stripe. ^[7] These bats are known as N. l. leporinus. In eastern Bolivia and the drainage basin of the Río Paraná south of the Brazilian Highlands and north of latitude 30° S, bats tend to be the largest and palest of the species. ^[7] They are known as N. l. rufescens.

Ecology and behavior

The greater bulldog bat lives primarily in tropical lowland habitats.^[8] The bats are commonly found over ponds and streams. They also found above estuaries of major rivers and bays and lagoons along coastlines.^[9] They live in colonies that number in the hundreds. ^[5] In Trinidad, bulldog bats frequent hollow trees including silk-cotton, red mangrove and balatá.^[10] The bats live in hollow tree roosts in other areas as well.^[5] They also use deep sea caves for roosting.^[10] Like most bats, bulldog bats are nocturnal.

Female bulldog bats stay together in groups while roosting and tend to be accompanied by a resident male. Females associate with the same individuals and in the same location, for several years regardless of turnover in resident males and movements of the group to alternate roosts.^[11] Males residing with female groups retain their tenure for two or more reproductive seasons.^[11] Bachelor males roost solitarily or in small groups apart from females. Female bats forage solitarily or in small groups with other females from the same roost group. Stable female roost groups forage together and return to the same foraging areas over long periods of time. ^[11] Males foraged solitarily, utilizing areas that were different from, and larger than, those of the females. ^[11]

Food and hunting

The greater bulldog bat is one of the few bat species that has adapted to eating fish. Nevertheless, the bats eat both fish and insects. During the wet season, the bats feed primarily on insects like moths and beetles.^[2] During the dry season, bat will primarily feed on fish as well as crabs, scorpions and shrimp to a lesser extent.^[2] The bulldog bat mostly forages for fish during high tide and locates them with echolocation. A bulldog bat will perform circular high flight searches. A bat in high search flight reacts to jumping fish with "pointed dips" at the spot where a fish has broken the surface. As it descends to the water surface the bat shows the typical approach pattern of all bats with decreasing pulse duration and pulse interval.^[12]

Bulldog bats also make pointed dips during low search flight by rapidly snapping the feet into the water at the spot where it has localized a jumping fish or disturbance. ^[12] In this raking mode, the bat drops to the water surface, lowers its feet and drags its claws through the water in relatively straight lines for up to 10 m. When raking, the bat uses two strategies. In directed random rakes it rakes through patches of water where fish jumping activity is high.^[12] In memory-directed random rakes, when there is no jumping fish, it starts to make very long rakes in areas where it has hunted successfully before after flying for several minutes without any dips.^[12]

Echolocation

Greater bulldog bats emit echolocation signals that are either at constant frequency (CF), frequency-modulated (FM) or a combination of the two (CF-FM) .^[12] In CF, pulses begin at 60kHz but may have a terminal downward sweep in frequency that does not drop below 50kHz. ^[5] A FM involves a CF beginning at about 60kHz that is modulated downward in frequency more than one octave.^[5] The CF component of the CF-FM signals averages 8.9 ms, the FM sweeps 3.9 ms. The CF components have frequencies of 52.8–56.2 kHz and the FM components have an average bandwidth of 25.9 kHz.^[12] The pure CF signals are the longest, with an average duration of 13.3 ms and a maximum of 17 ms. ^[12]

Reproduction cycle

For females, pregnancy occurs from September until January, and lactation starts in November and continues until April.^[4] Female bulldog bats give birth to single young each pregnancy.^[5] Male bats reproductive pattern with breeding mainly occurring in autumn and winter.^[5] Young bats do not leave the roost to attempt to make sustained flight until they reach adult size, which is around one month.^[5] There may be a high degree of parental care in this species and both adult males and female stay in the roost with the young during this time.^[5]

Status

There are no major threats throughout its range. In Guatemala fish farmers are killing this species.^[1] It is threatened by water pollution and in Belize; the water level changed and restricted the range.^[1] Deforestation is also a threat.

References