Species Account: Noctilio leporinus
Taxonomy and Range
Noctilio leporinus belongs to the class Mammalia, the order Chiroptera, and the family Noctilionidae. This Neotropical bat, commonly called the fisherman bat or the greater bulldog bat, ranges from Sinaloa and southern Veracruz, Mexico to northern Argentina and Southern Brazil (Nowak, 1999). It can also be found in the Greater and Lesser Antilles as well as the Bahamas (Nowak, 1999). Noctilio leporinus usually roosts near streams and other moist areas below 200 meters in elevation (Eisenburg, 1989). Colonies of up to 75 bats (Eisenburg, 1989) are found in hollow trees, rock fissures, caves, and sea caves (Nowak, 1999). These roosts can be located by the strong and musky odor released by the fisherman bats that live in them (Macdonald, 2001).
The head and body length of Noctilio leporinus ranges from 98-132 mm (Nowak, 1999) with the male and female bats having an average head and body length of 96.9 mm and 91.3 mm respectively (Eisenburg, 1989). The weight of Noctilio leporinus ranges from 50-90 grams (Brooke, 1994) with the average weight being 67 grams for males and 56 grams for females (Eisenburg, 1989). This species is covered in short fur that sheds water easily (Macdonald, 2001). The upper parts of Noctilio leporinus are often bright orange in males and gray or dull brown in females (Nowak, 1999). Both males and females have a paler middorsal line and under parts (Nowak, 1999). This species is commonly referred to as the bulldog bat due to their resemblance to large mormoopids except for the existence of large upper lips in place of a moustache (Findley, 1993). The bulldog batıs lips are full and appear to be swollen. The upper lips are smooth but a dividing fold of skin under the nose creates a harelip effect. The bottom lips are also smooth but are marked by a wart in the middle under which lies semicircular folds of skin that continue down the chin, creating a bulldog-like appearance (Nowak, 1999).
The greater bulldog batıs nostrils are somewhat tubular and open forward and down (Nowak, 1999). Its ears are large, pointed, and slender and contain a tragus with a notched outer edge. The tail is more than half as long as the femur and its tip is free. The wings are long and narrow compared to other families of Microchiroptera (Nowak, 1999). The flight of Noctilio leporinus is stiff-winged and not very rapid. When a bat of this species is knocked into the water it has the ability to swim well, using its wings as a type of oar (Nowak, 1999).
Noctilio leporinusı other common name, the fisherman bat, comes from its specialized fish diet. However, the diet of Noctilio leporinus consists of both insects and fish (Brooke, 1994). During the wet season, from July until December, insects such as moths and beetles are the primary source of food (Brooke, 1994). During the dry season fish dominate the diet as well as small quantities of crabs, scorpions, and shrimp (Brooke, 1994). The fish eaten by this species can be up to 8 cm long (Macdonald, 2001).
Adaptations for Fishing
In order to be able to hunt fish, the speciesı hind legs and feet are very large (Nowak, 1999). The feet are equipped with long, sharp claws that drag through the water (Wimsatt, 1970). Also, the tibia and large calcar (heel extension) are strongly compressed as part of an adaptation for fishing (Wimsatt, 1970). As a result, the batıs feet and hind limbs form a streamlined bundle that creates minimum drag when pulled through the water during hunting (Wimsatt, 1970).
While the rostrum is unusually short and broad in this species, the cheek teeth are of the tuberculosectorial type and seem to be adapted for a piscivorous diet (Wimsatt, 1970). This type of long canine teeth are typical of bats that eat large proportions of beetles, which Noctilio leporinus does, but they also appear to be useful in quickly securing fish (Brooke, 1994). Other adaptations to aid in hunting fish include a strong, long calcar that is used to lift the tail membrane clear of the water while the bat swoops down to catch fish and high aspect ratio wings for efficient flight over water (Altringham, 1998). Low wing loading is also a useful adaptation in that it allows for slow flight and the transport of large prey (Altringham, 1998).
The fisherman bat uses echolocation to detect the presence of the fins of small fish sticking above the water as well as the ripples these fish make on the water (Suthers, 1965). The location of the fish as well as the speed and direction of movement are made knowledgeable to the bat through returning echolocation pulses (Wenstrup & Suthers, 1984). Noctilio leporinus uses both narrowband and broadband components in its echolocation (Macdonald, 2001) and calculates the velocity of fish through the use of updated distance information from the FM component of its pulses, rather than through a Doppler shift mechanism (Wenstrup & Suthers, 1984). Two different echolocation calls are emitted, one consisting of a CF (constant frequency) pulse beginning at 60 kHz with a downward sweep in frequency to 50 kHz and another CF pulse beginning at 60 kHz and modulated downward in frequency more than an octave (Hood & Jones, 1984). Both the CF and FM patterns have adapted to long-range sonar to aid Noctilio leporinus in catching fish (Novick, 1977). The maximum range of detection using echolocation has been found to be 1.8 meters in this species (Novick, 1977).
Once a fish has been detected, Noctilio leporinus strikes, impaling it on the claws of its feet and simultaneously lowering its wings to lift away from the water (Nowak, 1999). The fish is then transferred from the feet to the mouth. Prey can either be eaten while in flight or is stored in the cheek pouches to be brought back to the roost (Macdonald, 2001). In addition to this hunting method, Noctilio leporinus also trawls randomly by dragging its feet through the water in areas where fish activity is high over straight distances of up to 10 meters (Altringham, 1998). On average, an individual fisherman bat consumes 30-40 fish each night through the combination of these two methods (Nowak, 1999).
Ordinarily, Noctilio leporinus gives birth once a year and produces only a single young at one time (Eisenburg, 1989). Females form nursery colonies and breeding seems to be highly synchronous in strongly seasonal habitats (Eisenburg, 1989). Pregnancies occur from September until January and lactation begins in November and continues until April, which corresponds with the wet season that produces the greatest amount of fish and insects (Nowak, 1999). Reproductive data for males shows a reproductive pattern with breeding mainly occurring in autumn and winter (Hood & Jones, 1984). Young bats do not attempt sustained flight until they are nearly full grown, which occurs around one month of age (Hood & Jones, 1984).
Fossil Record and Conservation Status
The fossil record of Noctilio leporinus is largely unknown. Some specimens of the species have been found in late Pleistocene sites in Puerto Rico and Cuba, but this is the only record of a fossil (Martin, 1972). Currently, Noctilio leporinus is not threatened in terms of conservation status and is not considered an endangered species (Macdonald, 2001).
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March 13, 2004