26.

Rusty Pipistrelle

Pipistrellus rusticus

French: Pipistrelle rouille / German: Rostfarbene Zwergfledermaus / Spanish: Pipistrela campestre

Other common names: Rustic Pipistrelle, Rusty Bat, Rusty Pipistrelle Bat

Taxonomy. Scotophilus rusticus Tomes, 1861,

“Damaraland.” Restricted by O. Thomas in 1926 to Olifants Vlei, Damaraland, Namibia.

Pipistrellus rusticus seems to be sister to P. hesperidus based on genetic data and chromosomal similarities. Two subspecies recognized.

Subspecies and Distribution.

P.r.rusticusTomes,1861—scatteredrecordsfromWAfricafromSenegaltoEEthiopiaalongwithNUgandaandWCKenya.

P. r. marrensis Thomas & Hinton, 1923 — S Africa in SE Angola, Zambia, NE Namibia, N Botswana, Zimbabwe, and NE South Africa; perhaps also Malawi, although specimens from that region need to be reexamined and are not mapped here.

There is also a record from E Tanzania, although its subspecific identity is uncertain.

Descriptive notes. Head-body 44-46 mm, tail 19-32 mm, ear 7-7-12 mm, hindfoot 4-6 mm, forearm 24-31-2 mm; weight 3-4-5-1 g. The Rusty Pipistrelle is vibrantly colored. Subspecies marrensis is slightly smaller than nominate rusticus and has narrower rostrum. Pelage is soft and dense. Dorsum varies considerably between reddish brown, orangish brown, grayish orange, grayish brown, or medium brown, sometimes within same locality. Venter also varies between orange, yellowish orange, creamy orange, yellow, or cream, being darkest under chin and palest in pelvic region. Naked face is pale or medium brown; triangular ears are pale to medium reddish brown, with rounded tips. Tragusis ¢.50% the length of ear and widest near mid-height;it has straight anterior margin, smoothly convex posterior margin, rounded tips, and deep notch above basal lobe. Wing membrane varies between pale brown, dark brown, or reddish black and occasionally has narrow white hind border. Uropatagium is medium brown or reddish brown, occasionally with cream border, and is always paler than wing membrane. Baculum is curved upward near mid-height, bilobed at base with deep notch between two basal lobes, and bilobed at tip with two very small lobes, and it narrows gradually toward thin tip. Skull is small and gracile compared with other African Pipastrellus; braincase is of moderate relative height and breadth; interorbital region is of moderate relative breadth; rostrum is of medium length but relatively broad; forehead region is straight to weakly concave; I” is unicuspid, and I? is tiny and reaches only slightly above cingulum of I*; P* is usually present,tiny, rarely visible above gums, and displaced lingually; C' and P* touch; and lower molars are nyctalodont. Chromosomal complement has 2n = 42 and FNa = 50.

Habitat. Montane forests, riverine forests, savanna woodlands, coastal forests, scrubland, and dry and moist savannas at low and high elevations. Often found near water.

Food and Feeding. The Rusty Pipistrelle is insectivorous, foraging by slow hawking 3-18 m over dry riverbeds and open water. It flies low and comparatively smoothly.

Breeding. Rusty Pipistrelles are seasonally monoestrous. Litter size is two (occasionally one); young are born in about mid-November. During development, 1-5 embryos can be present, but only up to two become implanted in uterine walls. One embryo is then found in each uteri; uterus is bicornuate. Reproduction of male and female gametes occurs at completely separate times. Spermatogenesis occurs in summer (October-February), and testes regress by late autumn, storing sperm in epididymides. Mating occurs in autumn (April), and sperm is stored in females’ uteri through winter (April-August) until implantation. Implantation occursin late winter and early spring (September). Unlike most other bat species, amnion is formed by cavitation rather than folding. Births occur in late spring (November) after gestation of ¢.11-12 weeks. There might be some delayed embryonic development.

Activity patterns. Rusty Pipistrelles begin to forage at dusk and probably continue throughout the night. They roost in tree crevices, under bark, and in old buildings. They do not enter hibernation or prolonged torpor during winter, remaining active throughout. Call shape is steep FM/QCEF, with high intensity. Single call recorded in Waterberg, north-eastern South Africa, had peak frequency of 62-1 kHz, minimum frequency of 55-3 kHz, knee frequency of 57-6 kHz, bandwidth of 6-7 kHz, and duration of 3-1 milliseconds. Other reports from South Africa recorded mean start frequency of 77-8 kHz, end frequency of 46-8 kHz, peak frequency of 53 kHz, and duration of 2-8 milliseconds.

Movements, Home range and Social organization. Rusty Pipistrelles probably roost in small groups. A group of three individuals was found roosting in a tree in Zambia.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Rusty Pipistrelle is widespread and found in numerous protected areas. No major threats are known, but it is considered rare throughout its distribution.

Bibliography. ACR (2018), Hill & Harrison (1987), Kearney (2013i), Kearney et al. (2002), Kruskop et al. (2016), van der Merwe & Mostert (2005), van der Merwe & Rautenbach (1990), Monadjem, Taylor, Cotterill & Schoeman (2010), Monadjem, Taylor, Jacobs & Cotterill (20171), Patterson & Webala (2012), Rautenbach et al. (1993), Skinner & Chimimba (2005), Taylor, Sowler et al. (2013), Thomas (1926).