A group of mostly mid-sized pipistrelle-like bats of Africa and the northern continents are known as the serotines (Eptesicus) [species shown here is the one generally known simply as the Serotine E. serotinus: photo by Mnolf, from wikipedia]. Here in Europe this is – along with pipistrelles, noctules and long-eared bats – one of the most familiar of vesper bat groups. As we’ll see, this group is anything but boring: it includes some weird big-eared species as well as the only bats known to breed within the Arctic Circle and a ‘giant’ species that eats birds.
Substantial confusion has surrounded the affinities of serotines and they’ve often been grouped with the Hypsugo species, the African butterfly bats or silvered bats (Glauconycteris) and the false serotines (Hesperoptenus) (e.g., Hill & Harrison 1987, Koopman 1994, McKenna & Bell 1997). This assemblage of genera has, in turn, typically been regarded as close to pipistrelles, though with ‘pipistrelles’ corresponding to a huge group no longer thought to be natural (we’ll get to that mess later on). Besides karyotypic characters, serotines can be distinguished from pipistrelles (sensu lato) on the basis of their short, ‘not-sticklike’ baculum (pipistrelles – sensu lato – have an elongate, roughly ‘stick-like’ baculum) (Heller & Volleth 1984) [in the figure below - from Topál (1970) - note how massive and thick the baculi of Ia io and the two serotines are compared to the stick-like pipistrelle baculum at far right].
While some recent authors have indeed found serotines (and the Harlequin bat Scotomanes ornatus and Great evening bat Ia io) to form a clade with pipistrelles (Thabah et al. 2007, Gu et al. 2008), Roehrs et al. (2010) found serotines and the Harlequin bat to form a clade with the Arielulus pipistrelles (once included within Pipistrellus), the Silver-haired bat Lasionycterus noctivagans, the butterfly bats or silvered bats and the evening bats (Nycticeius) (Roehrs et al. 2010).
If serotines, butterfly bats and evening bats do form a clade, the names Eptesicini and Nycticeini (or Nycticeiini) are both available: Nycticeini Gervais, 1855 very much has priority (Eptesicini wasn’t used – I think – until published by Volleth & Heller (1984)), but Roehrs et al. (2010) noted that “more effort will be required to resolve the position of Nycticeius [and what impact it might have] on the nomenclature of this clade” (p. 1084) [the relevant part of the cladogram is shown here: if you need help, see the article on the vesper bat cladogram].
Serotines are also known as big brown bats or house bats (that’s not ideal, since ‘house bat’ is also widely used for the Scotophilus species). About 20 species are known; they occur across Eurasia, Africa and the Americas. One species – the Northern bat E. nilssonii [shown below; photo by Mnolf, from wikipedia] – seems to hibernate and breed north of the Arctic Circle (Rydell et al. 1994), making it unique among bats (various other vesper bats have been recorded breeding as far north as 61-64°N; the Arctic Circle is at 66°N). Typically, serotines are mid-sized, naked-muzzled, broad-winged bats that look and fly something like large pipistrelles. They have proportionally short, broad ears and short, blunt tragi. Oddities among the group include African species with white or translucent wing membranes and the also African E. floweri (given its own subgenus – Rhinopterus – by some authors), notable for the raised, scab-like tubercles present on its arms, legs and tail.
Some species are bats of desert and semi-desert habitats, like the Middle Eastern and central Asian Sind bat E. nasutus. Some authors put these ‘desert serotines’ into the subgenus Rhyneptesicus (Horáček et al. 2000): Agnarsson et al. (2011) found E. nasutus to group well away from the rest of Eptesicus, and to be in a sister-group relationship with the Western pipistrelle/Canyon bat/American parastrelle Parastrellus hesperus (looked at previously in the perimyotine article). If this is confirmed by additional studies, E. nasutus at least will need a new generic name, and won’t be a member of the serotine clade at all. Another supposed serotine subgenus – Amblyotus – includes serotines of desert habitats, and others more associated with northern, montane habitats (most notably the Northern bat).
Big-eared bats among the serotines: the South American Histiotus species
Among the strangest-looking of vesper bats are the South American big-eared brown bats (Histiotus). I say that they’re strange-looking because they have very large ears, yet look facially much like serotines. For this reason I’ve often wondered whether they’re close to Eptesicus yet have convergently evolved giant, Plecotus-like ears. Indeed, this sort of thing has been suggested by some authors (Tate 1942, Hill & Harrison 1987): Williams & Mares (1978) found that the karyotype of H. montanus was identical to that of the American Eptesicus group that includes the Big brown bat E. fuscus. Roehrs et al. (2010) referred to unpublished results (included in Roehrs’s 2009 PhD thesis) which show that Histiotus is actually nested within Eptesicus [photo below, from Acosta & Venegas (2006), shows H. laeophotis].
A few fossil bats have been suggested to have affinities with serotines, including Paleptesicus priscus and Hanakia feifari, both from the Miocene of Europe. However, the former is also said to be similar to Eudiscopus denticulus (Rossina et al. 2006), a peculiar Asian vesper bat that we’ll get to later on. What seem to be definite serotines are known, however, from the Early Miocene onwards (Ep. aurelianensis is from the Lower Miocene of Germany).
Ia io, another bird-eating giant (with a really short name)
Probably closely related to the serotines is the tropical Asian Great evening bat Ia io [shown here: photo from University of Bristol's excellent Bats in China site], apparently the biggest of all vesper bats (up to 63 g and with a wingspan of about 51 cm). The fabulously short technical name was supposedly invented by Oldfield Thomas (in 1902) specifically to be the shortest name ever given to a mammal. Two other big vesper bats – Parascotomanes beaulieui Bourret, 1942 from Laos and I. longimana Pen, 1962 from China – are now generally regarded as synonymous with I. io (Topál 1970).
As is discussed in a future article in this series, the discovery of bird-eating behaviour in the Greater noctule Nyctalus lasiopterus makes it likely that other similarly sized, similarly shaped vesper bats might also be (perhaps occasional) predators of small birds. And exactly this was confirmed in 2007 when bird-eating habits were reported in the Great evening bat (Thabah et al. 2007). In a Chinese population, about 82% of fresh droppings collected beneath roosting bats were composed of feathers, whereas feathers formed 90-100% of the droppings (by volume) in an Indian population. Bird bone fragments were also found in some of the Indian droppings. This bird-eating behaviour hasn’t (to my knowledge) been photographed or filmed, nor are there any artistic reconstructions depicting it. Until now…
The size, wing shape and flight style of this large species are all consistent with the idea that, like the Greater noctule, it is also an occasional avivore, chasing and catching flying birds during the migratory season. However, for much of the year the bulk of its diet is made up of beetles, moths and flies. Because Ia io is not at all closely related to noctules, their shared bird-eating behaviour surely evolved convergently, and I think it’s only a matter of time before the next bird-eating vesper bat is discovered. A fossil relative of the Great evening bat, Ia lanna, has been described from the Lower Miocene of Thailand.
Harlequins, sprites and the Silver-haired bat
The Harlequin bat Scotomanes ornatus is another Asian, serotine-like vesper bat, so-named for its unusually patterned pelage [photo here ©, from siamensis.org]. Dorsally, the ground colour is orange-brown but a white, wavy stripe runs along the spine and white patches are present around the throat and on each shoulder. The belly is dark brown (and hence darker than the dorsal surface: an unusual feature), but the sides of the ribcage beneath the wings are white. The face is naked and pinkish. Clearly, it’s an unmistakable animal. But not much else is known about it. It seems to mostly frequent lowland forest.
In the molecular phylogeny generated by Roehrs et al. (2010), the serotine + Harlequin bat clade is the sister-group to a clade that includes the Asian Arielulus ‘pipistrelles’, the Silver-haired bat and the butterfly bats. Close affinities between at least some of these taxa have been supported in other studies (Csorba & Lee 1999, Volleth et al. 2001, Lin et al. 2002). We’ll be coming back to butterfly bats in another article. As for the others…
The five Arielulus ‘pipistrelles’ – sometimes known collectively as sprites – occur throughout tropical Asia, from southern China to Borneo. Two are recently described: the Collared pipistrelle or Collared sprite A. aureocollaris Kock & Storch, 1996 (regarded as worthy of its own genus – Thainycteris – by some authors) and Necklace pipistrelle or Necklace sprite A. torquatus Csorba & Lee, 1999 (endemic to Taiwan) [A. torquatus shown here, from Professor Paul's Guide to Mammals. I couldn't find a better, available photo].
The Silver-haired bat [shown here, from wikipedia] is a North American, woodland species (it’s also known from Bermuda, and with an extra-limital record in the Bahamas). It has short, broad ears, a partially furred tail membrane, and a wing shape that permits particularly slow flight: it’s said to be the slowest-flying bat in North America. Fossils belonging to the Silver-haired bat extend back to the Pliocene.
And THAT brings us to the end… of our look at (most) members of Eptesicini. Next: the hypsugines! In case you haven’t noticed, I’m in a desperate hurry to get through this series. Didn’t I already say this?
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)
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 – -
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