Once upon a time, a huge variety of small to very small vesper bats – basically all of those that possess a simple tragus, a shortish face, two pairs of upper incisors and two upper and two lower premolars – were lumped together as the pipistrelles. You don’t have to have a detailed or expert knowledge of vesper bat diversity or morphology to realise that at least some of these characters are primitive across Vespertilionidae, or have evolved repeatedly in disparate lineages. When these observations are combined with the morphological and molecular differences present among the many species concerned, you can see why bat experts have often doubted the monophyly of ‘pipistrelles’ as traditionally conceived. Indeed, it now turns out that many ‘pipistrelles’ aren’t pipistrelles at all [composite below shows ‘Eastern pipistrelle’ at left (from here) and Common pipistrelle Pipistrellus pipistrellus (by Mnolf, from wikipedia) at right].
Here in Europe – where the history comes from – we’re ok: our pipistrelles are pipistrelles, since they’re the ones first given this name. But if you’re North American – sorry – your pipistrelles turn out not to be pipistrelles. I’m referring of course to the familiar little bats once known as the Western pipistrelle Pipistrellus hesperus and Eastern pipistrelle P. subflavus.
Goodbye ‘Western pipistrelle’… hello Canyon bat?
The Western pipistrelle [shown here, from wikipedia] is often white-bellied, yellowish-brown dorsally, and with a very dark face and ears. It’s the smallest of North America’s bats, with a mass of 3-6 g and wingspan of 19-23 cm. It occurs from Mexico north to Washington and is strongly associated across its range with rock faces, canyons and boulders. It roosts in cracks, crevices and among rocks and may also use rodent burrows. For these reasons some people have suggested that it should be known as the Canyon bat. Variation across its range has resulted in the recognition of seven ‘subspecies’ (see map below, from Hatfield (1936). It shows five, but a sixth – P. h. potosinus – was named in 1951 and a seventh – P. h. oklahomae – in 1959). How many of these might actually be valid phylogenetic entities is in doubt and I’m not sure if recent studies have recovered any distinct structure within the species.
It’s adaptable, able to forage in woodland, shrubland and desert habitats, and there are indications that it can fly even when at low body temperature (O’Farrell & Bradley 1977). In fact there are records of these bats foraging when the air temperature was -8°C; some researchers think that (in the warmer parts of their range) these bats are probably active year-round (O’Farrell & Bradley 1970, Geluso 2007). Remember: there are bats that hibernate when it gets cool, bats that migrate when it gets cool, but also bats that can tolerate the cool and just carry on as usual. At the other extreme, this bat is also happy to be out foraging when air temperatures exceed 30°C.
And goodbye ‘Eastern pipistrelle’… hello Tricolored bat?
The Eastern pipistrelle is typically yellowish-brown and with black wing membranes. Its forearms are reddish-orange [obvious in the adjacent image: photo from here]. Its hairs are distinctly tri-coloured, with black bases, light brown shafts and dark brown tips. This has led to the alternative name Tricolored bat (or Tri-colored bat), and some bat workers argue that this name should be used instead of the technically inaccurate ‘Eastern pipistrelle’. It’s one of North American’s commonest and most widespread bats, yet comparatively little is known about its ecology and natural history (a familiar theme with North American mammals: do not assume that your wildlife is well understood!*). High-aspect wings suggest a preference for foraging in open habitats and there are some reports where foraging has been observed over fields and above woodland canopies. It may well be an ecotone species, frequently eating harmful insects associated with agricultural habitats.
* That wasn’t meant to be a dig directed at North Americans – it’s true of everywhere.
Unlike the Western pipistrelle, it seems to be an obligate hibernator, even in the southern parts of its range. Like many other temperate-zone vesper bats, females store sperm during hibernation and don’t ‘allow’ their eggs to be fertilized until spring (they produce one or two babies). In terms of roost and hibernation sites, the Eastern pipistrelle is flexible, with the choice of sites including buildings, rock crevices, beneath Spanish moss on low branches, and also beneath branches in tree canopies. It occurs as far north as Nova Scotia and might persist here because it’s warm compared to the rest of eastern Canada.
There are some indications that the species is expanded westwards across the USA, with new records occurring across the whole western boundary of its range (from South Dakota to Texas) as well as in the southern limits of its range (New Mexico) (White et al. 2006). Range expansion has also occurred around the Great Lakes: apparently this is the result of the modification of Bear Cave (Michigan) that happened in 1939-40 (Kurta et al. 2007). In Europe, there’s been some suggestion that increasing numbers of Common pipistrelles have put pressure on rare populations of horseshoe bats. It’s therefore conceivable that an increase in the Eastern pipistrelle might, similarly, have affected populations of other, rarer bats in eastern North America – though I’m only throwing this out there as a possibility and haven’t heard of any evidence for it. A preference for east-facing caves as hibernating sites has been demonstrated (Briggler & Prarther 2003). [Adjacent Eastern pip image by Hammbeen, from wikipedia]
Of parastrelles and perimyotines
As noted at the start of this article, it’s often been suggested that a great many of the vesper bats conventionally lumped together as pipistrelles are not really close relatives. Rather, they seem to be superficially similar, short-faced, small vesper bats with no close relationship. Indeed, ever since the 1940s morphologists and geneticists have been noting how various of the species involved probably warrant separation. The two North American ‘pipistrelles’ are among the offenders, differing from undoubted, Old World species of Pipistrellus in bacular and dental anatomy as well as karyotype.
Hoofer & Van Den Bussche (2003) found both species to be substantially removed from pipistrelles proper, and in fact outside the clade that included serotines, pipistrelles and vespertilionins. Neither species grouped closely to any other taxon, so it was decided that both should be given their own generic names. P. subflavus – the ‘Eastern pipistrelle’ – became Perimyotis subflavus, incorporating a generic name proposed for this species in 1984.
The situation with P. hesperus is a little more complex. Horácěk & Hanák (1985, 1985-86) proposed the new name Parastrellus for this species, but never did so in formal fashion. Hoofer et al. (2006) argued that this rendered the name a nomen nudum and therefore established the name formally. The Western pipistrelle is therefore now Parastrellus hesperus. Given that bats in Pipistrellus are known as pipistrelles and bats in Falsistrellus are known as falsistrelles, it would be neat if bats in Parastrellus became known as parastrelles. Some people started doing this unofficially as soon as Hoofer et al. (2006) was published, and in 2008 at least one annotated checklist of American mammals did use ‘American parastrelle’ as the official name for what used to be called the Western pipistrelle (Manning et al. 2008).
We therefore now have the undesirable situation of there being three common names in use for this bat: the name ‘Western pipistrelle’ isn’t going to go away, and there’s also ‘Canyon bat’ and now ‘American parastrelle’. The new name ‘American perimyotis’ has been suggested for what used to be called the Eastern pipistrelle (Manning et al. 2008). And this is in addition to ‘Tricolored bat’.
Incidentally, the Western pipistrelle/Canyon bat/American parastrelle was (when first described in 1864) originally named as a new species of Scotophilus. This name is, as we saw recently, only used today for the house bats of the Old World, but back then it was also used for various North American bats and also for European pipistrelles. The historical nomenclature of vesper bats is a total nightmare and I’d like to mostly avoid it if that’s ok with you.
Whatever they’re called, are these two interesting little bats close relatives, or are they separate on the vesper bat tree? Opinions on this have differed but Roehrs et al. (2010) found them to group together in a clade close to the large (unnamed) clade that includes serotines, hypsugines, pipistrelles and noctules. There isn’t (yet) a formal name for the ‘American pipistrelle’ clade, but Roehrs et al. (2010) referred to it as “the perimyotine group”. Google indicates that ‘Perimyotini’ hasn’t yet been used in the literature, and we await further studies (for a discussion of vesper bat phylogeny see the article on vesper bat phylogeny) [Eastern pipistrelle/Tricolored bat/American perimyotis shown here].
Incidentally, Hoofer et al. (2006) noted that the Western pipistrelle/Canyon bat/American parastrelle is very similar to the African hypsugine Hypsugo musciculus (this had previously been noted by Karl Koopman). Whether these similarities reflect affinity or convergence remains interesting, for one because it would demonstrate that perimyotines are not exclusively American. I don’t think the idea has been properly tested since phylogenies haven’t included both species; like so many obscure bats, H. musciculus is very poorly known and molecular data is apparently unavailable. I haven’t covered hypsugines yet… patience, patience.
Anyway, that was rather more than I intended to say about just two species. Nevertheless, they have – historically – been ‘important’ and, as we’ll see later, they’ve been harbingers of doom in terms of their implications for the content of Pipistrellus sensu lato.
For previous Tet Zoo articles in the vesper bats series, see…
- Introducing the second largest mammalian ‘family': vesper bats, or vespertilionids
- The vesper bat family tree: of myotines, plecotins, antrozoins, and all those cryptic species (vesper bats part II)
- Bent-winged bats: wide ranges, very weird wings (vesper bats part III)
- Of southern African wing-gland bats, woolly bats, and the ones with tubular nostrils (vesper bats part IV)
- The many, many mouse-eared bats, aka little brown bats, aka Myotis bats (vesper bats part V)
- Long-eared bats proper: Plecotus and other plecotins (vesper bats part VI)
- Desert long-eared bats – snarling winged gremlins that take scorpion stings to the face and just don’t care (vesper bats part VII)
- Hairy-tailed bats: a tale of furry tails, red coats, cold tolerance, migration and sleeping out in the open (vesper bats part VIII)
- Robust jaws and a (sometimes) ‘greenish’ pelt: house bats (vesper bats part IX)
- Australasian big-eared bats, and how to (perhaps) single-handedly wipe out an entire species, 1890s-style (vesper bats part X)
- Antrozoins: pallid bats, Van Gelder’s bat, Rhogeessa… Baeodon!! (vesper bats part XI)
And for previous Tet Zoo articles on bats, see…
- Desmodontines: the amazing vampire bats
- Giant extinct vampire bats: bane of the Pleistocene megafauna
- Camazotz and the age of vampires
- Dark origins: the mysterious evolution of blood-feeding in bats
- A new hypothesis on the evolution of blood-feeding: food source duality involving nectarivory. Catchy, no?
- Oh no, not another giant predatory flightless bat from the future
- The most terrestrial of bats
- I stroked a pipistrelle
- Red bats
- We flightless primates
- Big animalivorous microbats
- Hidden in plain sight: discovering cryptic vesper bats in the European biota
- PROTOBATS: visualising the earliest stages of bat evolution
Refs – –
BRIGGLER, J., & PRATHER, J. (2003). Seasonal Use and Selection of Caves by the Eastern Pipistrelle Bat (Pipistrellus subflavus) The American Midland Naturalist, 149 (2), 406-412 DOI: 10.1674/0003-0031(2003)149[0406:SUASOC]2.0.CO;2
Geluso, K. 2007. Winter activity of bats over water and along flyways in New Mexico. The Southwestern Naturalist 52, 482-492.
Hatfield, D. M. 1936. A revision of the Pipistrellus hesperus group of bats. Journal of Mammalogy 17, 257-262.
Hoofer, S. R. & Van Den Bussche, R. A. 2003. Molecular phylogenetics of the chiropteran family Vespertilionidae. Acta Chiropterologica 5, supplement, 1-63.
– ., Van Den Bussche, R. A. & Horáček, I. 2006. Generic status of the American pipistrelles (Vespertilionidae) with description of a new genus. Journal of Mammalogy 87, 981-992.
Horáček, I. & Hanák, V. 1985-1986. Generic status of Pipistrellus savii and comments on classification of the genus Pipistrellus (Chiroptera, Vespertilionidae). Myotis 23-24, 9-16.
Kurta, A., Winhold, L., Whitaker, J. O. & Foster, R. 2007. Range expansion and changing abundance of the Eastern pipistrelle (Chiroptera: Vespertilionidae) in the Central Great Lakes region. The American Midland Naturalist 157, 404-411.
Manning, R. W., Jones, C. & Yancey, F. D. 2008. Annotated checklist of recent land mammals of Texas, 2008. Occasional Papers, Museum of Texas Tech University 278, 1-18.
O’Farrell, M. J. & Bradley, W. G. 1970. Activity patterns of bats over a desert spring. Journal of Mammalogy 51, 18-26.
– . & Bradley, W. G. 1977. Comparative thermal relationships of flight for some bats in the Southwestern United States. Comparative Biochemistry and Physiology Part A: Physiology 58, 223-227.
Roehrs, Z. P., Lack, J. B. & Van Den Bussche, R. A. 2010. Tribal phylogenetic relationships within Vespertilioninae (Chiroptera: Vespertilionidae) based on mitochondrial and nuclear sequence data. Journal of Mammalogy 91, 1073-1092.
White, J. A., Moosman, P. R., Kilgore, C. H. & Best, T. L. 2006. First record of the Eastern pipistrelle (Pipistrellus subflavus) from southern New Mexico. The Southwestern Naturalist 51, 420-422.