The California Leaf-nosed Bat (Macrotus californicus) is a species of bat in the family Phyllostomidae. It is found in Mexico and the United States. Its natural habitat is hot deserts. It is threatened by habitat loss.

Habitat

California leaf-nosed bats can be found in Sonoran and Mojave Desert scrub habitats in the Colorado River valley in southern California, Nevada and Arizona, and throughout western Mexico. It is non-migratory and does not hibernate.

Biology

Close-up view of California Leaf-nosed Bat

The California leaf-nosed bat weighs between 12 and 20 grams, has a wingspan of over 30 centimeters and a body length of over 6 centimeters, and is brown in color. As its name implies, it has a triangular fleshy growth of skin, called a noseleaf, protruding above the nose. This bat is the only bat of the family Phyllostomidae in the United States to have large ears, usually over 2.5 centimeters. It is also one of the most maneuverable in flight. With short, broad wings, it can fly at low speeds using minimal energy. Because of this adaptation, it is not suited for long-distance travel, and is non-migratory.^[2]

This bat has an unusual reproductive pattern. After breeding occurs in the fall, the embryos develop very slowly until March, when growth continues at a more normal rate before birth in May or June. Twins are common.^[2]

This bat is a "gleaning" insectivore which captures prey such as crickets, grasshoppers, beetles, and sphinx moths straight from the ground or foliage rather than in flight. It prefers to use its large eyes to detect prey, although in total darkness it will switch to echolocation. It typically hunts within a few feet of the ground, using its superior eyesight to search for insects. It does not alight to capture its prey, but hovers above it and snags it off the substrate. It then carries its prey to an open roost such as a porch or open building to dismember, then consume it.^[2]

Human Impact

They are susceptible to human disturbance, which can be especially detrimental to the species during summer months, when these bats are rearing young. Human disturbance of caves in which they roost is a major threat. Furthermore, because they often roost in abandoned mines, reclamation practices and re-working old mines can severely impact populations. Because California leaf-nosed bats do not hibernate or migrate, the relatively warm mine shafts are critical for its survival in the northern portions of its range.^[2]

Roosting habits and terrestrial locomotion

California. In the study area Macrotus roosts in the daytime exclusively in caves, deserted mine tunnels and deep grottos.^[3] They are usually within 30 to 80 feet of the entrance of the tunnel, and seemed not to require dark retreats. On many occasions leaf-nosed bats roost in tunnels less than 20 feet deep and fairly brightly lit. In order to be suitable the Macrotus retreat must be mostly enclosed and have overhead protection from the weather.^[3] Roosting chambers are usually large enough to provide considerable ceiling surface and flying space, and thus adequate space allows the animal to find a place to roost while flying. The coolness of the roost also plays a factor in Macrotus selection of roosts, which is why Macrotus would choose to roost in a cool cave in the hot summers. Macrotus prefer to hang from sloping parts of the ceiling and actively grab the rock with ease due to the irregularity of the surface.^[3] the bat seems to rest much of the time while hanging onto the rock with only one foot. The free foot is often used for scratching and for grooming the fur, a when the bat is engaged in these activities the body usually swings gently like an erratically disturbed pendulum.^[3]

Foraging habits and flight

The flight of the Macrotus Is remarkable chiefly for its extreme maneuverability. The bat flies fairly rapidly on occasion, but the usual foraging flight is slow and buoyant, and more nearly silent that of most bats.^[3] In level flight Macrotus wings make a soft fluttering sound that is less sharp and carrying than the sounds made by the wing beats of most other bats. The method of landing is most interesting. The bat flies six to eight inches below the ceiling and upon the wings making a deep down stoke that is directed nearly straight forward the hind limbs and uropatagium.^[3] These movements cause the bat to swoop upward toward the ceiling and as the bat nears the ceiling the wings are pulled back in an upstroke while the bat rolls over 180 degrees so that its back is facing downward and the long legs reach for the ceiling.^[3] Stated briefly, then the alighting maneuver consists of an upward swoop and a half-roll, at the end of which the feet wing rapidly toward the ceiling, seize it, and the wings give a final beat to steady the bat. Often these landings must require remarkably precise judgement of speed and distance, as many landings are made in the midst of a fairly closely spaced group of bats.^[3] Macrotus has two main methods of launching into flight, by dropping form the ceiling and taking flight after a short downward swoop, and by taking flight directly form the roosting place. The bat often hovers, both when foraging and when flying in its daytime retreat. Macrotus seems to hover easily, and it’s able to hover for several seconds at a time. These bats usually forage within three feet of the ground and often drop down closer to the ground nearer the surface where they can occasionally hover for a few seconds.^[3] Even bats released in the daytime flew fairly close to the ground. Leaf-nosed bats seem to be totally insectivorous, and their food clearly reflects the bats’ foraging habits. Some insects regularly eaten by Macrotus are almost certainly taken from the ground or from vegetation. The bats’ stomachs often contain orthopteran insects, noctuid moths and caterpillars, and beetles of the families Scarabaeidae and Carabidae, along with unidentified material.^[3] The lists of food items of Macrotus contain a plethora of insects that seldom fly, are flightless, or that fly in the daytime; this constitutes strong evidence that this bat consumes insects that are on the ground or on vegetation. Most leaf-nosed bats forage sometime between one hour after sundown and four hours after sundown, and then retire to a night roosting place. Actually, each bat seems to have a pre-midnight foraging period of roughly one hour.^[3] The greatest activity in the early morning seems to occur between two and one half hours before sunrise and thirty minutes before sunrise. Bats generally begin returning with full stomachs to their daytime roosts about tow hours before sunrise, and the last bats usually return approximately twenty minutes before sunrise.^[3]

Effect of diet on basal heat production

Insect feeders Insectivorous more closely resemble temperate zone taxa in their proclivity to relax thermoregulatory control when at rest and in their tendency to have lower basal metabolic rates.^[3] This apparently results form the fact that insectivorous species tend generally to be smaller and gain considerable metabolic savings by reducing body temperature ambient temperature differentials.^[3]

Aerodynamic considerations

Most bats have upper wing loadings than do birds, and he mentioned that this difference my be due to the way bats forage. Most insectivorous birds forage by making repeated, short flights. Bats, on the other hand, remain on the wing for most if not all of the time they are foraging, and insects are captured by virtue of bats ability to maneuver rapidly.^[3] In birds the slots formed by the alula and primary flight feathers allow these animals to have high wing loadings and fairly low staling speeds. In the unslotted wings of bats the wings do not yield such refinements in flight characteristics, but within the size and wing loadings of bats there is little need for increasing lift. In comparison the flight of bats is much is clearly less efficient than that of birds. The upstroke consumes relatively more power in bats than in birds because the wing surfaces in bats are continuous and do not allow the passage of air as do the spaces between the primaries of a bird.^[3]

Lift

Irregular membranes known as the propatagium (the membrane anterior to the humorous and radius) shape the wing. The plagiopatagium (membrane posterior to the humorous)has a greater surface than the chiropatagium (membranes between the digits), particularly the fifth, the position of the hind limb, which anchors the posterior edge of the plagiopatagium, and by the angles that the propatagium and dactylopatagium minus (membrane the second and third digits) make with the posterior parts of the wing membranes. Air pressure against the ventral surfaces of the wing membranes is greater than that against the dorsal surfaces; this helps to maintain a smoother camber.^[3] Macrotus californicus seems to spread its uropatagium widely only when hovering or performing other maneuvers requiring a departure form straight level flight, but the extreme maneuverability observed in Macrotus californicus is probably due to the specializations of its sensory equipment.^[3]

Bone anatomy

In Macrotus the position of the hind limbs during level flight differs even more form that in most other mammals. The hind limbs are held behind the bat in a spider-leg- like posture, with the femur extending dorsad and caudad, and with the shank partially flexed and extending caudad and more or less downward.^[3]

Vertebral column The number of post cervical vertebrae in Macrotus are as follows: twelve thoracic, six lumbar, five sacral, seven caudal.^[3]

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References

• Species Profile at Bat Conservation International. [1].
• Vaughan, Terry A. Functional Morphology of Three Bats: Eumops, Myotis, Macrotus. 1st ed. Vol. 12. KC: University of Kansas Museum of Natural History, 1958. Print.
• Baker, Robert J., J. Knox. Jones, and Dilford C. Carter. Biology of Bats of the New World Family Phyllostomatidae. Lubbock: Texas Tech, 1976. Print.