290.

North American Evening Bat

Nycticeius humeralis

French: Nycticée vespérale / German: Neuweltabendsegler / Spanish: Nicticeo vesperino

Other common names: Black-shouldered Bat, Twilight Bat

Taxonomy. Vespertilio humeralis Rafinesque, 1818,

Kentucky, USA .

Nycticerus cubanus has been treated as a subspecies of N. humeralis, but smaller body size (total length less than 85 mm), smaller forearm (less than 32: 4 mm), and smaller condylo-basal length (less than 13- 2 mm) of N. cubanus separate both species; their distributions are also very distinct. Three subspecies are currently recognized.

Subspecies and Distribution. N.h.humeralisRafinesque,1818—fromSOntarioinCanada,andMichiganinUSASacrossmostEUSA,extendingWtoSENebraska,CKansas,COklahoma,andETexas.

N.h.mexicanusW.B.Davis,1944—EMexico(fromTamaulipasSalongtheGulfcoasttoVeracruz).

N. h. subtropicalis Schwartz, 1951 — S Florida.

Descriptive notes. Head-body ¢. 56 mm, tail 35-41 mm, ear 11-14 mm, hindfoot 8-10- 8 mm, forearm 33-39 mm; weight 6- 4-14 g. Females are slightly larger than males. The North American Evening Bat is similar to the Big Brown Bat ( Eptesicus fuscus), which is distinguished by its larger size and presence of two pairs of upper incisors, and some species of Myotis, from which it can be separated by short and blunt tragus and presence of only one pair of upper incisors. Dorsal hairs are bicolored, with dark brown bases and light ash-gray tips. Venter is similar to dorsum, but contrastis more conspicuous between hair bases and tips, and tips are paler, sometimes tawny. Muzzle and membranes are hairless, and tail extends less than 1 mm beyond uropatagium. Ears are also naked, small, and dark. Tragus is short, broad, and blunt. Facial glands are pronounced. Skull is robust, short, broad, and low. Lower teeth are similar to those of Eptesicus; teeth are relatively small; I* is simple, unicuspid, and separated from C' by small gap; area of crown of M? is one-halfthe size of crowns M' and M?, with mesostyle, metacone, and three commissures evident. Dental formulais 11/3, C 1/1, P1/2,M 3/3 (x2) = 30. Chromosomal complement has 2n = 24 and FN = 48.

Habitat. Deciduous forests, gallery forests of sabinos (7axodium mucronatum, Cupressaceae) and sycamore ( Platanus, Platanaceae), and river corridors and wetlands from sea level up to elevations of ¢. 900 m.

Food and Feeding. Fecal analysis of North American Evening Bats indicated that beetles were one of the most abundant items on their diets, constituting ¢.50% of total volume ingested by some individuals. Moths and leathoppers are also abundant items; less frequent items are bedbugs, cicadas, true bugs, caddisflies, and flying ants. They have a slow and steady flight, foraging at heights of 12-23 m in the beginning of the night and much closer to the ground after dark. Foraging takes place over clearings, farm ponds, and openings in trees along watercourses. Tails and wing membranes are used to capture prey in flight during feeding maneuvers. Individuals from the same roost apparently share information about location of foraging patches, and unsuccessful individuals foraging alone might follow groups to better foraging areas.

Breeding. Male North American Evening Bats can mate with up to 20 females, probably in late summer and early autumn. Females store sperm until spring when ovulation and fertilization occur. Females then usually give birth to twins, but one or three young were also recorded; births occur in May-July. Newborns are pink and naked. Exudates produced in the submaxillary glands of females are used to mark and locate individual offspring by odor. After six weeks, young males leave colonies, and females stay. Males and females will reproduce in the year following to their birth.

Activity patterns. North American Evening Bats are crepuscular and nocturnal, and they fly shortly after sunset and before dawn. They are rarely found in caves, preferring to roost in hollow trees, under bark, in buildings, in hay (7illandsia, Bromeliaceae), and under palms. Echolocation calls sweep from 50-80 kHz to 20 kHz at 60-65 dB. Pulses of 0-4-2 milliseconds sweep from 85 kHz to 40 kHz in a pulse rate of 30-35 seconds. Predators include snakes, raccoons, hawks, and domestic cats.

Movements, Home range and Social organization. North American Evening Bats are social and form colonies with ¢.30 individuals. During winter, they are absent in the northern parts of the distribution and migrate southward. An individual was recovered 547 km south of the place it was banded. During autumn, they accumulate large reserves of fat to perform long migrations or hibernate. Migrant females arrive at maternity colonies in late April to early May, and usually all individuals have already left colonies by mid-October. During migrations, sexes segregate, with males remaining south throughout the year and females migrating northward to congregate in maternity colonies of less than a dozen up to 950 individuals. Homing distances of 61-153 km were reported. North American Evening Bats will occupy buildings with Brazilian Free-tailed Bats (7adarida brasiliensis); single adult male Big Brown Bats were found in maternity colonies.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Population trends of North American Evening Bats have not been monitored, and the US Fish and Wildlife Service do notlist it as a species of concern. It is considered threatened in Indiana, where it has been better monitored. One of the major threats might be the loss of roosting and forage habitats. In Mexico, it is probably affected by construction of dams along rivers in the north-east that destroy gallery forests.

Bibliography. Agee (1969), Baker & Patton (1967), Barbour & Davis (1974), Cope & Humphrey (1967), Hall (1981), Kurta (2001), Linzey & Brecht (2005), Moreno (2014), Neely (2003), Simmons (2005), Solari (2019¢c), Varona (1974), Watkins, (1972), Whitaker & Clem (1992), Wilson & Ruff (1999).