California Leaf-nosed Bat, Macrotus californicus

California Leaf-nosed Bat, Macrotus californicus. Collected from a cave within the Las Cuevas area of Baja California Sur, January 2018. Wing Span: 28 cm (11 inches); body 5.8 cm (2.3 inches). Catch courtesy of Sam Rousseau, Raleigh, North Carolina and Brad Murakami, Surrey, British Columbia, Canada.

The California Leaf-nosed Bat, Macrotus californicus, is member of the Phyllostomidae family of Bats.  The Phyllostomidae family has one hundred fifty-one members placed in forty-nine genera. There are only two species in the Macrotus genus. Currently, there are one hundred thirty-seven different bat species known in Mexico that are known as Muerciélagos. The California Leaf-nosed Bat is known in Mexico as Murciélago Orejón Califoriano de Nariz Foliforme.

California Leaf-nosed Bats are large in statute and grayish to dark brown in color and are named for a triangular fleshy growth of skin protruding from their nose. The sexes are similar in size and appearance, weighing between 12 grams (0.4 oz) and 20 grams (0.7 oz). They have wingspans of 30 cm (12 inches) and body lengths of 6.2 cm (2.4 inches). They have large ears that are in excess of 2.5 cm (1.0 inch) in length, and their hearing is so good that they can hear the footsteps of a cricket. Their hind limbs are held behind their body in a spider-leg-like posture and a uropatagium extends between their thighs. They have large eyes and short and broad wings. California Leaf-nosed bats are one of the most maneuverable bats in flight, spreading their uropatagium widely when performing flight maneuvers, a skill attributed to specialized sensory equipment. They can fly at low speeds using minimal energy and can hover for several seconds at a time. They fly fairly rapidly on occasion, but their usual foraging flight is slow and buoyant. In flight, their wings make a soft fluttering sound that is less sharp and travels less distance than the sounds made by the wing beats of most other bats. They fly 6 to 8 inches below the ceilings of caves and land with remarkable precision. Typically, their landing maneuver consists of an upward swoop and a half-roll, at the end of which their feet swing rapidly toward the ceiling, seize it, and their wings give a final beat to steady themselves. They have two main methods of launching into flight; by dropping from the ceiling and taking flight after a short downward swoop, and by taking flight directly from the roosting place.

California Leaf-nosed Bats mate in the fall. Males seek out special areas in caves or mines solely for the purpose of courting, while females arrive at the male sites in groups after dark. As the females fly past, the males put on vigorous wing-flapping displays and vocalize. After some deliberation, a female may land next to a male or allow one to approach her. The male then nuzzles her and attempts to wrap his wings around her as a prelude to copulation. Competing males will often attempt to disrupt the couple by boxing the courting male or flying into him. Unlike other species, California Leaf-nosed Bats do not have delayed fertilization and become pregnant soon after mating. The embryos develop very slowly over the winter, followed by a three-and-a-half-month period of rapid development in spring. Interestingly, neither increased roost temperature nor a greater food supply will speed embryonic development in winter. The eight-month gestation period ensures that the young are born in late spring, at a time when mothers are able to support them. In May or June, each mother produces a single pup, which she nurses for about a month. Pups are born with their eyes and ears open and a body that is already furred. In summer, adult females form maternity colonies that typically consist of 100 to 200 females. A few dominant males remain with the maternity colony, each guarding a group of 5 to 25 mothers and pups. Female pups reach sexual maturity in their first fall, only a few months after birth, while male pups do not become sexually active for another year. They have an average life-span of twenty to thirty years in the wild.

California Leaf-nosed Bats are not suited for long distance flying and are thus non-migratory. They do not hibernate but will undergo brief periods of reduced body temperature. They roost during the day in caves within geothermally heated rocks, deserted mine tunnels, and deep grottos. They are typically found within 10 m (30 feet) to 24 m (80 feet) of the entrance of the cave and seem to not require dark retreats. On many occasions, Leaf-nosed Bats are found roosting in caves that are less than 6 m (20 feet) deep and fairly brightly lit. In order for it to be suitable, the roosting chamber must be mostly enclosed and have overhead protection from the weather. Roosting chambers are usually large enough to provide considerable ceiling surface and flying space. Roosting during the day provides escape from summer heat and the drying effects of desert climate, protection from the winter cold, and protection from the weather. They hang from sloping parts of the ceiling by one foot or both feet, usually swinging gently like a pendulum. They typically emerge one to two hours after sunset in summer and at sunset in winter. Emergence is variable and groups may emerge from a roost over several hours. They return to roost about one hour before sunrise. The California Leaf-nosed Bat is a “gleaning” insectivore, consuming beetles, crickets, grasshoppers, and sphinx moths straight from the ground or from foliage while hovering above in flight. Prey is detected normally by eye sight but they also have the ability to hunt in total darkness via echolocation. The captured prey is hauled away to an open roost (open buildings, cellars, porches, bridges, rock shelters and mines) where it is dismembered and consumed. In turn, they are preyed upon by cats, coyotes, owls, raccoons and snakes.

From a conservation perspective the California Leaf-nosed Bat is currently considered to be of Least Concern due to their wide distribution and occurrence in a number of protected areas. This species was previously listed as vulnerable by the IUCN but was relisted as  Least Concern in 2008. Human entry into mines or cave roosts, closure of mines for hazard abatement, and renewed mining are the primary threats to the California Leaf-nosed Bat. Loss of desert riparian habitat has also been attributed to the population declines. Cave roosts are critical for maternity colonies in the spring and summer and surviving the winter. Gating caves identified as significant roosts, for hundreds of individuals within maternity colonies, can be an important conservation action.