393.

Fish-eating Myotis

Myotis vivesi

French: Murin pécheur / German: Fischfressendes Mausohr / Spanish: Ratonero pescador

Other common names: Fish-eating Bat

Taxonomy. Myotis vives: Menegaux, 1901,

Isla Partida, Baja California, Mexico .

Subgenus Pyzonix; vives: species group (1 species). Myotis vives: 1s tentatively included in subgenus Pyzonix due to morphological characters, but molecular phylogenies do not support this arrangement. Peculiar morphologicaltraits of M. vives: arise from adaptations to piscivory, and it does not have an evolutionary history independent of Myotis . It has been recovered in a New World Myotis clade, at times found as sister to the clade containing Nearctic species, such as M. lucifugus, M. occultus, and M. fortidens (mitochondrial approaches), or as sister to the clade containing the Neotropical Myotis (nuclear approaches). R. N. Platt and collaborators in 2018 provided a detailed discussion of these issues. Monotypic.

Distribution. Coastal NW Mexico, including areas in Sebastian Vizcaino Bay and Tortuga Bay on Pacific coast, Gulf of California from C Baja California (Islas Esmeraldas) to Bay of Paz and Punta Coyotes in Baja California Sur, and from Bay of San Jorge S to Guaymas in Sonora; also on many islands.

Descriptive notes. Head-body ¢. 85-88 mm, tail 50-78 mm, ear 20-26 mm, hindfoot 22-24 mm, forearm 53- 7-63 mm; weight 22-28 g. The Fish-eating Myotis is distinguished from other New World Myotis by its larger size, remarkably developed legs (21-2-24- 8 mm long), prominent claws, and long feet. Furis long (dorsal fur 7-9 mm) and silky. Dorsal hairs are bicolored, with dark brown bases and dark buffy to paler cinnamon tips. Ventral hairs are bicolored, with light gray bases, white tips, and little contrast between bases and tips. Ears are comparatively long, extending forward 5 mm beyond nostrils. Antitragusis long, and anterobasal lobe is comparatively small. Membranes are dark brown. Tail projects just beyond free border of uropatagium. Margin of plagiopatagium is attached to knee by remarkable narrow band of membrane and has hemorrhagic nodules between forearm and fifth finger; feet and claws are very long and laterally compressed; and calcar is long and folds forward along lower part of hindlimb. Dorsal surface of uropatagium is covered with hairs on distal one-third, and on underside, there are a few hairs at base. Baculum is not saddle-shaped, differentiating it from New World congeners; distaltip is not knob-shaped but tapers to flattened slightly elevated tip, and lacks ventral spurs on proximal margin. Skull is large (greatest skull lengths 21-23- 8 mm); parietal is inclined forward; occipital region is generally slightly rounded posteriorly; and sagittal and lambdoidal crests are present, ranging from low to medium. Incisorsare typical of Myotis; cingulum on C, forms small cusp anteriorly; teeth cusps, especially on canines and premolars, are taller and thinner than in other Nearctic Myotis; second premolar is taller than first premolar; and M? is not reduced. There is a rudimentary protoconule on M! and M2. In mandible, heightening of second premolar is so great that profile of entire row of cusp summits does not abruptly fall in front of large premolar that is so characteristic of cusp profile of Myotis . Chromosomal complement has 2n = 44 and FN = 50, with three large and one small metacentric and 17 medium to small acrocentric pairs of autosomes. Xchromosome is medium submetacentric, and Y-chromosome is small submetacentric.

Habitat. Coastal areas with xeric shrubland, every so often with cactus and dispersed bushes, close to sea level.

Food and Feeding. Fish-eating Myotis forage over waterin coastal areas and fly low and rather slowly while foraging over open marine lagoons, nearly skimming the water. Prey is captured with long claws of hindfeet and quickly transferred to the mouth. Prey is consumed during flight or at a perch. Marine fishes and crustaceans are main foods, which can be complemented with insects and occasionally algae.

Breeding. Testicles of Fish-eating Myotis are smallest in January and increase slightly from February to June and reach maximum size in October. Mature spermatozoa are found in males from late July through September. Mating period is not known, and there is evidence that sexes partially segregate after mating. Seasonal separation of male spermatogenic activity and female gestation suggests that females store sperm. Pregnant females were found in March—May. Small maternity groups of 2-8 females were found in a single rock crevice. During this period, males often are found isolated. Gestation lasts 55-65 days; females give birth to one young between late May and early June. Newborns are 71-75 mm long and weigh 5-9-6- 6 g. Body weight quadruples and length double in ¢.50 days. Young have been observed resting on their mother’s back in the day roost, but females have not been observed carrying young while foraging. Young first fly at ¢.50 days of age, but lactation continues even after young start to fly.

Activity patterns. Fish-eating Myotis begin to forage at dusk and return to roosts before dawn. They fly directly from day roosts to feeding areas at sea and sometimes return to day roosts during the night. Main roosts include rock slides, caves, and rock crevices but under large flat rocks along the beach and under turtle shells not exposed to direct sun. Presence of predators (native and introduced), population pressure, temperature, and relative inclination of roost are factors that influence presence or absence at any locality. Wings are long, and tips are relatively elongated and rounded, characteristic of bats that fly in open uncluttered areas. Echolocation calls have steep descending FM sweeps from 45 kHz to 20 kHz, duration of 3 milliseconds, and a second harmonic. Mean repetition rates are 10-20 calls/second at a distances of ¢. 2 m from the target.

Movements, Home range and Social organization. Island subpopulations of Fisheating Myotis separated by large expanses of open water maintain high genetic diversity and high rates of gene flow, suggesting frequent movement among islands. Fish-eating Myotis form small colonies and sometimes share day roosts with petrels (Hydrobates sp.).

Status and Conservation. Classified as Vulnerable on The IUCN Red List. Population of the Fish-eating Myotis has declined by more than 30% over the last three generations due to the effects of introduced predators. It has a severely fragmented distribution and 1s declining in its area of occupancy. Recolonization of restored habitat is low, and females show strong philopatry, so is more vulnerable to habitatloss.

Bibliography. Arroyo-Cabrales & Ospina-Garces (2016e), Avila-Flores & Medellin (2014), Baker & Patton (1967), Blood & Clark (1998), Flores-Martinez et al. (2005), Floyd et al. (2010), Maya (1968), Menegaux (1901), Miller (1906), Miller & Allen (1928), Otalora-Ardila et al. (2013), Platt et al. (2018), Ruedi & Mayer (2001), Stadelmann, Herrera et al. (2004), Suthers (1967).