Pipistrelles proper: little bats that glide, sing, swarm and lek (vesper bats part XVIII)

Among the best known, most widespread and most familiar of vesper bats are the pipistrelles. All bats conventionally regarded as pipistrelles are small (ranging from 3-20 g and 35-62 mm in head-body length), typically with proportionally short, broad-based ears and a jerky, rather erratic flying style.

Compared to the majority of vesper bat species, the better known pipistrelle species (the common European species Pipistrellus pipistrellus and P. pygmaeus) are well known and well studied in terms of ecology and behaviour [composite above shows Common pipistrelle in various poses, with Rüppell's pipistrelle P. rueppellii at middle bottom]. They catch small insects in flight, typically along hedgerows, tree lines and in woodland clearings, and often in close vicinity to water. They use narrowband calls (where bandwidth is less than 15 kHz) when hunting in open spaces but switch to broadband calls (bandwidths c. 69 kHz) when foraging in more cluttered habitats. Even when using broadband calls, they seem to put most of the call's energy into the narrowband 'tail' part of the call. This flexibility - combined with their small size, preference for small flies and readiness to use buildings for roosting - makes pipistrelles particularly good at exploiting urban and suburban habitats, and helps to explain why they're among the most abundant bats of cities, towns, villages and parks, at least here in Europe.

Their wings have a high aspect ratio and their wing-loading is low [pip in flight here by Barracuda1983, from wikipedia]. They're fast, agile fliers, frequenting swooping and twisting. Pipistrelles intersperse their rapid wingbeats with short, often steep glides (about 13% of their flight time involves gliding) (a mode of flight that involves brief bouts of gliding is - rather confusingly - termed 'undulating flight'). They sometimes turn during these glides and often accelerate during the glides too. They might employ this style of flight for the purposes of energy conservation (Thomas et al. 1990).

Another important possible consequence of gliding is that the bats might not be able to echolocate during this part of their flight (because echolocation pulses are linked to wingbeats): this perhaps explains the wide gaps in pipistrelle echolocation pulses that have sometimes been recorded (Thomas et al. 1990). One rarely considers or reads about gliding behaviour in bats, and it's little studied. However, in pipistrelles at least it's readily observed (I currently get to watch it every night) and it seems to be important - physiologically and behaviourally - to these little bats. There are some indications that gliding is used more than usual during songflight behaviour (on which see below).

Singing, swarming and lekking: the hectic social lives of pipistrelles

Pipistrelles have an interesting social life and do lots of peculiar things that remain all but unknown to most people unfamiliar with the bat literature. Actually, many of the components of behaviour I'm about to discuss are widespread in vesper bats.

After leaving the summer maternity roosts, both the adult females and the year's young begin searching in traditionally favoured areas for the winter's roost sites. Common pipistrelles at least form large aggregations of hundreds of individuals (most typically noted in the empty rooms of houses) termed invasions or swarms though they aren't, technically, the same thing as the swarms that occur - mostly around cave mouths and mine shafts - in other vesper bat species. Adult males live on their own during the summer and, during late summer and autumn, occupy territories that they defend from other males. These are surprisingly large: up to 200 m in diameter (Sachteleben & von Helversen 2006).

Males use songflight to attract females - that's right, male bats use aerial vocal displays to attract females - and it's been shown that the more time a male spends in songflight, the more females he can attract [adjacent illustration - by Tom McOwat, from Altringham (1999) - shows a male Common pip in songflight]. One interesting recent discovery is that some females with new babies will visit territory-holding males and even stay in their roosts (BartoniÄka et al. 2008). Roost-switching (and movement of flightless babies) was common in a studied population of P. pygmaeus mothers. A displaying male calls near the roost he is advertising, but also calls while circuiting the territory, occasionally chasing away intruding males. Males are also observed to make 'false landings' during their display flights, and it's suspected that they might be indulging in some sort of scent-marking. The calls used during songflights include components audible to human ears; outside of the breeding season, some of the calls involved serve an agonistic function (Barlow & Jones 1997).

It's typically been thought that the males are defending (and advertising) a desirable roost location. Furthermore, they mate with several or many females. For these reasons it's often been said that male pipistrelles practise resource-defence polygyny (e.g., Gerell & Lundberg 1985). However, some studies indicate that the males position their territories close to (not at) the winter roost sites desired by the females: the females therefore have to pass through the male territories (which are densely packed and arranged in a periphery around the area where the winter roosting sites are), and the males make no effort to prevent females from leaving. Because the females are confronted with a variety of closely spaced, displaying, territory-holding males, and because they have choice over potential mates, this system might be seen as a form of lekking (Sachteleben & von Helversen 2006). [The diagram below - from Sachteleben & von Helversen (2006) - shows Common pipistrelle territories and roost sites in Bayreuth, Germany. Note that the stars (marking 'songflight territories') are arranged around the triangles (winter roost sites) and dotted circles ('invasion sites')].

Not all pipistrelles attract females by calling while in flight: Nathusius' pipistrelle P. nathusii [shown here, by Mnolf, from wikipedia] at least may call while hanging from the roost entrance (a behaviour also seen in noctules). Some pipistrelles (like Nathusius' pipistrelle) are highly migratory, occasionally being encountered on North Sea oil platforms (Russ et al. 1998) and sometimes making trips to their winter hibernacula of up to 1600 km.

Exploding Pipistrellus

Until very recently, all 70-odd species referred to as 'pipistrelles' were united in the single genus Pipistrellus. The presence of distinct 'species clusters' then led to the creation of seven pipistrelle 'subgenera': Pipistrellus of the Old World and Australasia, Vespadelus of Australasia, Perimyotis of North and Central America, Hypsugo of Eurasia, Africa and North America, Falsistrellus of Asia and Australasia, Neoromicia of Africa, and Arielulus of Asia (Nowak 1999). Naturally, some authors have regarded various of these subgenera worthy of generic rank and hence separate from pipistrelles sensu stricto. Better yet, several phylogenetic studies (predominantly based on molecular data) have found some of the subgenera to be but distantly related (Hoofer & Van Den Bussche 2003, Hoofer et al. 2006, Roehrs et al. 2010): as we've seen in the previous parts of this series, the bats I just listed are now treated separately as the perimyotines, or as members of the hypsugine clade and serotine clade.

Accordingly, the name Pipistrellus is used here in the more restrictive fashion supported by recent analyses. It includes the European pipistrelles but also some Asian and Australasian species like P. paterculus of India and south-east Asia, P. coromandra of central, southern and south-east Asia, and the widespread P. tenuis (Roehrs et al. 2010). Palaearctic species seem to form three clade: (1) the predominantly African P. kuhlii clade (also present across Europe and the Canary Islands), (2) an east Asian clade that includes P. abramus and the Japanese pipistrelles P. endoi and the mysterious P. sturdeei, and (3) a west- and central Asian clade of desert and semi-desert specialists (HoráÄek et al. 2000) [adjacent photo of P. rueppellii by Richard Randall, from African Bat Conservation News 21. According to HoráÄek et al. (2000) this species doesn't fit into any of the three groups just listed].

However, even this restricted version of Pipistrellus is paraphyletic, as noctules seem to fall within the clade subtended by the species I just mentioned (see the cladogram shown below: the dotted box shows the species currently included within Pipistrellus]. It might be acceptable to include noctules within Pipistrellus - after all, it could be argued that noctules do look much like gigantic, big-toothed, fast-flying pipistrelles - but such revised nomenclature is unlikely to be accepted wholesale. An alternative would be to create new names for the pipistrelle species clusters that are distinct from the clade that includes P. pipistrellus, the type species.

Hello Afropipistrellus

An African pipistrelle until recently included in the hypsugine species Neoromicia flavescens was argued by Thorn et al (2007) to warrant separation as the true pipistrelle species P. grandidieri. Not only does this species actually belong within Pipistrellus proper, it was also argued to be 'distinct enough' relative to other pipistrelles to warrant the creation of a new 'subgenus': Afropipistrellus (diagnostic characters include a proportionally short tibia, long outer incisor and relatively small brain) [P. grandidieri skull shown here, from Thorn et al (2007)].

Given that all of the other 'subgenera' proposed for pipistrelles are now regarded either not as pipistrelles at all (examples: Vespadelus, Perimyotis, Hypsugo, Falsistrellus and Neoromicia), or as junior synonyms of Pipistrellus, Afropipistrellus currently stands as the only accepted division within this clade. P. grandidieri seems to be widespread across Africa, but is (apparently) nowhere common.

Cryptic species (again) and the history of pips in Europe

In Europe, a large amount of research has centred around the discovery of cryptic species within what used to be regarded as the single species P. pipistrellus (the Common pipistrelle) [this subject was previous covered in Hidden in plain sight: discovering cryptic vesper bats in the European biota]. The existence of a slightly different species - now most often called the Soprano pipistrelle P. pygmaeus - is now well accepted, but additional studies have shown that even the 'revised' version of P. pipistrellus contains additional species-level taxa in northern Africa (Benda et al. 2004, Hulva et al. 2004, 2010). Benda et al. (2004) found Libyan bats in the P. pygmaeus lineage to be significantly different genetically and morphologically from other members of the complex (they have a proportionally robust rostrum and large canines), and therefore named them as the new species P. hanaki. [Cladogram below - topology based on that recovered by Roehrs et al. (2010) - shows paraphyly of Pipistrellus as currently conceived].

The deep divergences within this species complex seem to have happened about 3 Ma ago, with north African and Mediterranean lineages being the oldest. This matches with the fact that pipistrelles are entirely absent from the Pleistocene fossil record of central Europe and seem to have spread rapidly across the region during the Holocene (HoráÄek & Jahelková 2005). Hulva et al. (2004) suggested that the deepest divergence within the P. pipistrellus complex was driven by the Messinian salinity crisis (an event that resulted in the near-dissappearance of the Mediterranean Sea and aridification of the Mediterranean region).

The European pipistrelles are - as you may have gathered from the contents of this article - pretty well known and much-studied. Alas, the same cannot for said for a great many of the others. Photos and good information are unavailable for the vast majority of them, and most can be regarded as poorly known. The Christmas Island Pipistrelle P. murrayi has declined chronically within recent decades and hasn't been seen since August 2009 (when the last known individual disappeared from its regular foraging and roosting areas). Sturdee's pipistrelle Pipistrellus sturdeei - reportedly collected on Hahajima Island in the Bonin Islands, Japan, and known only from the holotype - might also be extinct, but there are suspicions that the locality data is inaccurate.

Next: noctules, the remaining members of Vespertilionini. Then we're (just about) done.

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)
• Putting the 'perimyotines' well away from pips proper (vesper bats part XII)
• Nycticein bats: apparently, a nice example of how assorted distant relatives can be mistakenly considered close allies on the basis of one or two characters (vesper bats part XIII)
• Eptesicini: the serotines and their relatives (vesper bats part XIV)
• Hypsugines: an assemblage of 'pipistrelle-like non-pipistrelles' (vesper bats part XV)
• A list of enigmas: bamboo bats, frogs-head flyers, Rohu's bat and the false serotines (vesper bats part XVI)
• Lobed bats, butterfly bats, particoloured bats, thick-thumbed bats, Dormer's bats, bats, bats, BATS... did I mention the bats? (vesper bats part XVII)

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 - -

Altringham, J. D. 1999. Bats: Biology and Behaviour. Oxford University Press, Oxford.

Barlow, K. E., & Jones, G. (1997). Function of pipistrelle social calls: ï¬eld data and a playback experiment Animal Behaviour, 53, 991-999

BartoniÄka, T., Bielik, A. & Åehák, Z. 2008. Roost switching and activity patterns n the soprano pipistrelle, Pipistrellus pygmaeus, during lactation. Annales Zoologici Fennici 45, 503-512.

Benda, P., Hulva, P. & Gaisler, J. 2004. Systematic status of African populations of Pipistrellus pipistrellus complex (Chiroptera: Vespertilionidae), with a description of a new species from Cyrenaica, Libya. Acta Chiropterologica 6, 193-217.

Gerell, R. & Lundberg, K. 1985. Social organisation in the bat Pipistrellus pipistrellus. Behavioral Ecology and Sociobiology 16, 177-184.

Hoofer, S. R. & Van Den Bussche, R. A. 2003. Molecular phylogenetics of the chiropteran family Vespertilionidae. Acta Chiropterologica 5, 1-63.

- ., Van Den Bussche, R. A. & HoráÄek, I. 2006. Generic status of the American pipistrelles (Vespertilionidae) with description of a new genus. Journal of Mammalogy 87, 981-992.

HoráÄek, I. Hanák, V. & Gaisler, J. 2000. Bats of the Palearctic region: a taxonomic and biogeographic review. Proceedings of the VIIIth European Bat Research Symposium 1, 11-157.

- . & Jahelková, H. 2005. History of the Pipistrellus pipistrellus group in Central Europe in light of its fossil record. Acta Chiropterologica 7, 189-204.

Hulva, P., Fornůskova, A., Chudárková, A., Evin, A., Allegrini, B., Benda, P. & Bryja, J. 2010. Mechanisms of radiation in a bat group from the genus Pipistrellus inferred by phylogeography, demography and population genetics. Molecular Ecology 19, 5417-5431.

- ., HorácÄk, I., Strelkov, P. P. & Benda, P. 2004. Molecular architecture of Pipistrellus pipistrellus/Pipistrellus pygmaeus complex (Chiroptera: Vespertilionidae): further cryptic species and Mediterranean origin of their divergence. Molecular Phylogenetics and Evolution 32, 1023-1035.

Nowak, R. M. 1999. Walker's Mammals of the World, Sixth Edition. The Johns Hopkins University Press, Baltimore and London.

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.

Russ, J. M., O'Neill, J. K. & Montgomery, W. I. 1998. Nathusius' pipistrelle bats (Pipistrellus nathusii, Keyserling & Blasius 1839) breeding in Ireland. Journal of Zoology 245, 345-349.

Sachteleben, J. & von Helversen, O. 2006. Songflight behaviour and mating system of the pipistrelle bat (Pipistrellus pipistrellus) in an urban habitat. Acta Chiropterologica 8, 391-401.

Thomas, A. L. R.Jones, G., Rayner, J. M. V. & Hughes, P. M. 1990. Intermittent gliding flight in the pipistrelle bat (Pipistrellus pipistrellus) (Chiroptera: Vespertilionidae). Journal of Experimental Biology 149, 407-416.

Thorn, E., Kock, D. & Cuisin, J., 2007. Status of the African bats Vesperugo grandidieri Dobson 1876 and Vesperugo flavescens Seabra 1900 (Chiroptera, Vespertilionidae), with description of a new subgenus. Mammalia 71, 70-79.