Now that all the fuss about modern-day sauropod dinosaurs has died down, we can get back to the serious business of vesper bats (incidentally, I do plan to cover the mokele-mbembe – in serious fashion – at some point in history). For previous parts in the vesper bats series, please look at the links below.
A group of about 17 species of American bats (occurring from Alberta down to Chile and Argentina) are known collectively as the hairy-tailed bats or hoary bats (Lasiurus*) (together with the Silver-haired bat Lasionycterus noctivagans, they’re also sometimes known as tree bats).
Most hairy-tailed bats are woodland animals that capture insects in flight, though Eastern red bats L. borealis at least will alight on vegetation to pick off insects. They are short-snouted with rounded ears that don’t extend beyond the limits of their thick pelt. They have high wing-loading and relatively slender wings and are fast, manoeuvrable fliers. [Adjacent painting of a Hoary bat L. cinereus by Carel Brest van Kempen (of Rigor Vitae), used with permission.]
* The generic name Lasiurus is also in use for a grass.
As is the case with many vesper bat genera, the taxonomic status of various populations has been the subject of debate, and certain populations currently regarded as species (including the Minor red bat L. minor, Pfeiffer’s red bat L. pfeifferi and Western red bat L. blossevillii) have been regarded as subspecies of other taxa in the past. A few South and Central American species have been discovered comparatively recently, like the Tacarcunan bat L. castaneus from Panama, named in 1960, the Cuban red bat, named in 1961, the Blackish red bat L. ebenus from Brazil, named in 1994, and Handley’s red bat L. atratus from Venezuela, Guyana, Surinam and French Guiana, named in 1996.
As suggested by their common collective name (and generic name*), hairy-tailed bats have thick fur covering the tail membrane and at least some species are well insulated from the cold: the Hoary bat in particular is well known for regularly flying when conditions are freezing (there is also a lot of fur on the wing membranes, even around the wrist). The tail membrane is used like a blanket during roosting, sometimes being folded right over the animal’s face as well as its chest and belly. Indeed, while most bats of temperate environments shelter inside tree hollows, buildings and caves, hairy-tailed bats roost and even hibernate outside, typically hanging from leaves or branches (roosting close to or even on the ground has been recorded too) [the adjacent photo, by Anne-Marie, shows an Eastern red bat hanging from a branch]. In what I presume is a further heat-saving adaptation, they often hang from just one foot.
* Lasiurus means ‘hairy tail’
There are some indications that the Eastern red bat has recently increased its Canadian range northward, perhaps as a result of climatic warming (Willis & Brigham 2003) [Eastern red bat photo above by USGS, from wikipedia]. A less well known species, the Southern yellow bat L. ega, might also have increased its range recently – this time in the south-western USA – thanks to increased roosting opportunities provided by newly planted ornamental palm trees (Spencer et al. 1988). This latter species is one of four or five species (the others are the Northern yellow bat L. intermedius, Western yellow bat L. xanthinus, Big red bat L. egregius and Cuban yellow bat L. insularis) once regarded as belonging to the separate ‘genus’ Dasypterus. These ‘yellow bats’ are not to be confused with the Scotophilus species, also sometimes called yellow bats, nor with the Rhogeessa bats, often called little yellow bats (I haven’t covered those groups yet).
The red ones
A few hairy-tailed bat species are notable for possessing reddish fur (sometimes described as brick red), and quite why they’re so red remains a good question (camouflage of some sort is the most popular explanation) [images below show the ventral and dorsal surfaces of a Western red bat photographed in Brazil. Note the thick pelt and large amount of fur on the wing – not just close to the body but also around the wrist. Images kindly provided by Guilherme Siniciato Terra Garbino]. All the more interesting is that Eastern red bats are generally thought to exhibit sexual dimorphism in coat colour, with males being redder than the reddish-grey females (e.g., Shump & Shump 1982): I mentioned this as a ‘fact’ when writing about red bats back in November 2007. Dimorphism in coat colour is really rare in mammals… lemurs and gibbons come to mind.
Anyway, Davis & Castleberry (2010) recently used museum specimens to show that – when body size and the time of year at which the animal was collected were taken into account – sex was less significant than the other two factors. Smaller individuals tend to be redder, and because males are generally smaller than females (recall the previous discussion of sexual size dimorphism in vesper bats), males tend to be redder. Also of interest is that older museum specimens tend to be the reddest, apparently because a longer history of handling has resulted in erosion of the original light-coloured or buffy tips to the hairs (Davis & Castleberry 2010).
Migration, and flying to Hawaii, Cuba, Jamaica and… the Orkney Islands!
Some hairy-tailed bats are migratory, in cases moving from southern Canada or the northern US to the far southern US. The evidence for this slowly built up from about the 1840s and has mostly been based on the seasonal appearance of large numbers of the bats in certain areas, especially on islands (to take one good example: their regular appearance on the Farallon Islands – first reported in the 1960s – only seems explainable via seasonal migration). Other bits of evidence supporting migration include observations of flocks seen moving rapidly in daylight and occasional landings on ships out at sea. Cryan (2003) also said that the several cases in which these bats have been seen to collide with buildings supported a migratory habit, though I’m not sure why: maybe because this behaviour indicates rapid flight through an unfamiliar area.
As you might expect for a group of long-distance migrants, hairy-tailed bats have been good at colonising islands: there are species within the clade that are endemic to the Galapagos Islands (L. brachyotis*), Cuba (L. pfeifferi and L. insularis) and Jamaica (L. degelidus). The Hoary bat is the supreme disperser in the group and has colonised the Hawaiian islands, appears occasionally on Iceland and Cuba, and has even managed (at least once) to get across the Atlantic and as far east as the Orkney Islands (Hill & Yalden 1990) [adjacent Hoary bat photo by BLM, from wikipedia].
* L. brachyotis is highly similar to L. borealis and was argued by Koopman & McCracken (1998) to be a subspecies of this taxon.
A fossil Eastern red bat is known from the Middle Pleistocene sediments of Bermuda – a place used today as a refuge during migration. It implies that the migratory behaviour of this species was established at least by this time (Grady & Olson 2006). Incidentally, Pliocene occurrences of both Eastern red bats and Western red bats indicate that both species have been distinct for at least 3.5 Ma (Czaplewski 1993). This provides additional evidence that they really are species rather than subspecies, as thought prior to 1988. A few other Pliocene occurrences of Lasiurus are known: an extinct species (L. fossilis) has been named from the Rexroad Formation of Kansas and also occurs in the Glenns Ferry Formation of Idaho (Czaplewski 1993) [adjacent images of Western red bat skull by David Nagorsen and Mark Brigham, from Bats of British Columbia and used in the Electronic Atlas to the Wildlife of British Columbia].
One remarkable feature of the migratory habit present in some species is that the sexes of L. cinereus (the Hoary bat) segregate in different parts of North America during the summer: females (and their young) go east, and males go west. Another unusual feature of Lasiurus bats is that females seem to typically (i.e., not just occasionally) produce more than two young at a time, and in this they are unique among bats as a whole. Litters of two or three are common, but four and five are on record too. Apparently, old records show that females used to carry their babies when they went on foraging trips, yet more modern records of such behaviour are absent. Does this really mean that behaviour has changed within the species concerned, or is it that the old records are just unreliable?
Lasiurini – what the hell kind of bats are you, really?
Hairy-tailed bats have historically been recognised as distinct at ‘tribal’ level relative to other vespertilionine vesper bats, and exactly how they might related to the other vespertilionines has yet to resolved. As I said in some of the previous articles in this series, Roehrs et al. (2010) found hairy-tailed bats to be nested within an assemblage that includes the plecotin long-eared bats; specifically, they were the sister-taxon to the American long-eared bats (Corynorhinus). This is a fairly surprising result. For one thing, it would suggest that hairy-tailed bats had secondarily evolved short ears from big-eared ancestors. This possible position is shown – in simplified form* – in the adjacent cladogram (for more discussion of the vesper bat cladogram see the article on the vesper bat cladogram).
* The cladogram depicts hairy-tailed bats and long-eared bats as if they’re sister-taxa; this isn’t technically correct for reasons just explained. I hope you can forgive me for producing a simplified, diagrammatic cladogram: for the technical, detailed version, see Roehrs et al. (2010).
Equally surprising is Agnarsson et al. (2011) recovery of hairy-tailed bats as the sister-taxon to the antrozoins (pallid bats and kin). Extremely modified, short-eared long-eared bats, or close kin to the robust-jawed, big-toothed pallid bats? As usual, more work is needed before we can be confident either way. Whatever, it doesn’t stop these neat, thick-furred, cold-tolerant, highly mobile, often migratory bats from being any less fascinating.
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)
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 – –
Agnarsson, I., Zambrana-Torrelio, C. M., Flores-Saldana, N. P. & May-Collado, L. J. 2011. A time-calibrated species-level phylogeny of bats (Chiroptera, Mammalia). PLoS Currents 011 February 4; 3: RRN1212. doi: 10.1371/currents.RRN1212.
Cryan, P. M. 2003. Seasonal distribution of migratory tree bats (Lasiurus and Lasionycteris) in North America. Journal of Mammalogy 84, 579-593.
Czaplewski, N. J. 1993. Late Tertiary bats (Mammalia, Chiroptera) from the southwestern United States. The Southwestern Naturalist 38, 111-118.
Davis, A. K. & Castleberry, S. B. 2010. Pelage color of red bats Lasiurus borealis varies with body size: an image analysis of museum specimens. Current Zoology 56, 401-405.
Grady, F. V. & Olson, S. L. 2006. Fossil bats from Quaternary deposits on Bermuda (Chiroptera: Vespertilionidae). Journal of Mammalogy 87, 148-152.
Hill, J. E., & Yalden, D. W. (1990). The status of the hoary bat (Lasiurus cinereus) as a British species. Journal of Zoology, 222 (4), 694-697 DOI: 10.1111/j.1469-7998.1990.tb06026.x
Koopman, K. F. & McCracken, G. F. 1998. The taxonomic status of Lasiurus (Chiroptera, Vespertilionidae) in the Galapagos Islands. American Museum Novitates 3243, 1-6.
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.
Shump, K. A. & Shump, A. U. 1982. Lasiurus borealis. Mammalian Species 183, 1-6.
Spencer, S. G., Choucair, P. C. & Chapman, B. R. 1988, Northward expansion of the southern yellow bat, Lasiurus ega, in Texas. The Southwestern Naturalist 33, 493.
Willis, C. K. R. & Brigham, R. M. 2003. New records of the Eastern red bat, Lasiurus borealis, from Cypress Hills Provincial Park, Saskatchewan: a response to climate change? Canadian Field-Naturalist 117, 651-654.