Over the course of the previous 19 – yes, 19 – articles we’ve looked at the full diversity of vesper bat species (see links below if there are any parts you’ve missed). If you’ve been following the series on an article-by-article basis, you’ll hopefully now have a reasonable handle on the morphological, behavioural and ecological variation present within this enormous, fascinating group, and will also have some idea of how the many different kinds of vesper bats might be related to one another. We’ve seen how bent-winged bats, wing-gland bats, tube-nosed bats, woolly bats and mouse-eared (or little brown) bats belong outside a major clade that includes long-eared bats, hairy-tailed bats and the serotines, pipistrelles and noctules. I feel extremely satisfied that I managed to get through the whole series; thanks to those of you who helped in obtaining literature, or provided comments, criticisms or congratulations.
As a palaeontologist, I think a lot about the life of the past. But I also think a lot about the life of the future. Do vesper bats have a future in a world that is so destined to change as a result of human-caused climate change, habitat loss and their associated effects? On the one hand, a group that contains over 400 species appears destined to survive, especially when members of several disparate lineages seem to be doing reasonably well in modern, human-dominated environments. I can image that pipistrelles and little brown bats, for example, will continue to hunt around parklands and gardens so long as trees and insects continue to exist.
On the other hand, we’re learning fast that new and totally unexpected problems can affect whole groups of organisms in the modern world – the spread of the amphibian-killing chytrid fungus Bd is one of the most nefarious examples – apparently as a cascading consequence of climate change and ecosystem collapse. And the fossil record shows us that groups including tens or hundreds of diverse species may not always weather catastrophic environmental events. Sad to say, there are many clues from the world of bats that all is not well, and that these mammals are potentially vulnerable to extinction. In fact, already things are downright worrying. In this last article in the vesper bat series, we’ll look at some of the various problems facing vesper bats today, ending with the most serious.
Disturbance and roost destruction
Many vesper bats are hibernating animals that require secluded winter roost sites with specific climatic conditions. Not only are the right sites in relatively scarce supply, human disturbance (caused by industry, development and also recreation and exploration) can make them unsuitable. Deliberate vandalism and carelessness by naïve spelunkers have led to bats abandoning roost sites. This is not a trivial problem. To take an extreme example (that, admittedly, doesn’t involve vesper bats): the roost at Eagle Creek Cave in Arizona [shown here, from Angie McIntire's Holy Batblog Batgirl!] consisted of more than 30 million Mexican free-tailed bats Tadarida brasiliensis in the 1960s, but was reduced to approximately 30,000 by the 1990s due to deliberate vandalism (mostly shooting but also dislodging of flightless babies) and disturbance. Declines in some mouse-eared bat species have been attributed to human disturbance at roosts: in 22 summer colonies of Grey bat Myotis grisescens in the mid-west US, the number of individual bats declined by 75% between pre-1968 and 1976 (Tuttle 1979), and similar declines have been reported in other species and other places, sometimes with the populations disappearing entirely (e.g., bent-winged bat colonies in western Europe). Many important roosts are now sealed off with special gates or grilles to reduce disturbance.
The permanent sealing of mineshafts and destruction of old buildings like churches have also resulted in the loss of important roost sites, and the practise of removing dead and/or hollow trees in some areas has also contributed to bat decline [the adjacent photos show a Polish mine - used as an important hibernaculum by both barbastelle and Greater mouse-eared bat - in its original condition (above) and (below) after it was illegally filled-in during March 2010. From here].
Given that bats of some (and probably many) species rely on traditional roost areas, the removal of one or a few sites in a region could well result in the deaths of the bats that normally travel to the region. They lack sufficient energy reserves, and the required experience or knowledge, to find another suitable roost in time.
People have deliberately poisoned bats in order to remove them from buildings but chemicals used to treat woodwork (and protect it from boring insects) – in particular organochlorine pesticides and gamma-HCH – are also known to kill roosting bats and have been implicated in bat decline in western Europe and elsewhere.
Wind turbines and death by barotrauma
It’s been known for some time now that wind turbines are also killing large numbers of bats. The numbers of bats being killed is pretty staggering: during a six-week period, a study conducted in 2003 estimated that between 1700 and 2900 bats had been killed at just two wind farms in West Virginia and Pennsylvania. Some studies report bat deaths numbering in the low hundreds every single night at specific wind farms. [An Enercon E 126 turbine shown below (I have no idea whether this particular turbine, or kind of turbine, is involved in bat deaths). Image by Jfz, from wikipedia].
These figures might not sound catastrophic (though in the long term they probably are). However, many of the affected bat species are at low populations already and hence of conservation concern. Both migratory and non-migratory species have been killed, but migratory species are most affected. Taller turbines kill more bats than shorter ones. The phenomenon isn’t local, but has been reported wherever there are inshore turbines and people monitoring them: in the USA, Canada, the UK, and across continental Europe (especially Portugal, France and Germany).
Quite why and how turbines cause fatalities in bats is an interesting problem. Direct collisions cause death, and observations show that bats often don’t notice spinning turbine blades until it’s too late. It’s well known (particularly to people who live near turbines) that wind turbines generate noise, and the suggestion has been made that this somehow attracts bats. However, testing has not provided support for this idea. It has also been proposed that bats are attracted to turbines because they mistake them for trees, or because they approach them to hunt insects, but neither idea seems well supported.
However, apparently the biggest cause of mortality results from barotrauma: that is, rapid pressure change caused by the turbines results in fatal lung damage. Baerwald et al. (2008) autopsied turbine-killed bats and found that 90% of the corpses exhibited internal injuries consistent with barotrauma [adjacent figure - from Baerwald et al. (2008) - shows bat lungs with evidence of pulmonary barotrauma. See the paper for the details]. Data from other small mammals shows that relatively little pressure change is required to kill via internal injury. Birds are, seemingly, not as adversely affected since their respiratory system (with its stiff lungs) is better able to cope with the shunting around of large quantities of air (birds do get killed by turbines, but predominantly by collision with the blades. The results are messy).
Turbines as a cause of fatality haven’t been ignored or unstudied, but have actually formed the focus of several detailed reports. Here in the UK, the Bat Conservation Trust has been involved in several major studies: go here if you want to access some of the (freely available) documents. A recently proposed solution to reduce the number of bat deaths at turbines involves fitting radar emitters to the turbines (Nicholls & Racey 2007): the bats seem to avoid these.
Global habitat loss
One of the greatest problems facing bats worldwide is habitat loss. As we’ve seen in this series, a large percentage of vesper bats are tropical animals of rainforests, woodlands and grasslands. The destruction and degradation of these habitats through deforestation, increased livestock grazing and drought – some of this linked to climate change – results in loss of bat habitat, and also in the resources that bats require. A large number of bats worldwide appear to be in decline as a result, with some of the best studied examples involving tropical fruit bats. [Adjacent photo of forest destruction in Mexico by Jami Dwyer, from wikipedia].
However, bats of all kinds are definitely being affected by logging and forest disturbance: there are too many studied examples to list them, but population declines of 50% or more have been documented or extrapolated in forest-dwelling vesper bats from Africa (e.g., the tropical long-eared bat Laeophotis namibensis), Madagascar (e.g., the house bat Scotophilus borbonicus) and tropical Asia (e.g., the tube-nosed bat Murina ussuriensis). As we’ve seen throughout this series, species across most vesper bat lineages are now suspected of being extinct, or close to extinction. Note that, because many of the species in this large group are little studied, our knowledge of their conservation status is often poor to non-existent.
The substantial role that bats play in providing ecosystem services – in particular they suppress pest insect populations* – means that their decline and extinction will have a serious effect on ecosystem stability, and potentially on agriculture and human health. Many bats (certain phyllostomids, fruit bats and others) are important pollinators and seed dispersers. Their decline and extinction would likely be catastrophic.
* A single bat eats more than 1000 small insects during every hour of foraging.
A new worrying problem, as yet without a simple solution, is known as white-nose syndrome (WNS). First identified in New York state in 2006, this fatal fungal disease had been reported from over 115 caves and mines across north-eastern North America, from Tennessee in the south to Quebec and Ontario in the north [map below shows spread as of January 2010: any data on new occurrences would be appreciated]. Affected bats have white growths of the recently named cold-living fungus Geomyces destructans on their snout, wings, ears and other exposed tissues (the fungus was named as new in 2009: see Tom Volk’s excellent page here and Gargas et al. (2009); see also Blehert et al. (2009)). The fungus causes the bats to use up their fat reserves and die, though whether it’s the fungus itself responsible for death or a secondary agent remains uncertain [Adjacent pic of infected Little brown bat Myotis lucifugus from wikipedia].
Enormous numbers of bats have been killed (over 1 million since 2006) belonging to seven different species. Mortality is as high as 90% in some affected hibernacula; the floors of such places are littered with piles and piles of dead bats (as well as dead bats still hanging from the ceilings and walls). Among the most severely affected species is the Little brown bat, a previously widespread and abundant vesper bat that was apparently on the increase due to successful conservation measures. Based on the current trend in decline, Frick et al. (2010) extrapolated a 99% chance of local extinction for this species within the next 16 years. This is from a starting population of about 6.5 million.
Needless to say, the spread of WNS is of major concern [images here and below from Zooillogix: they covered WNS back in April 2010]. Caving activity has been prevented in the areas where it occurs in case people are acting as vectors but it looks more likely that bats spread it themselves.
In 2009, G. destructans was reported from a Greater mouse-eared bat Myotis myotis captured in France. Genetic sequencing and morphological analysis showed the French G. destructans to be 100% identical to North American samples. However, the infected bat wasn’t underweight and subsequent monitoring at the site and those nearby didn’t reveal any die-offs like those observed in North America. While it remains possible that WNS may yet strike European bat populations, so far it seems either that European bats are immune, or that a secondary agent is involved and has yet to strike in Europe (Puechmaille et al. 2010).
The rapid spread and catastrophic impact of the disease, combined with its presence in an apparently healthy French bat, suggests that it is native to the Old World and that its recent appearance in North America is entirely novel (Frick et al. 2010). Like Bd in amphibians and colony collapse disorder in bees, it may be that so-called pathogen pollution is going to become a growing problem, with increased global traffic, climate change and sequential ecosystem collapse all combining to expose naïve species to novel diseases. This is a rather pessimistic outlook, but it’s difficult not to be pessimistic after seeing the results of the WNS outbreak, or when considering how the data indicates that a species consisting of millions of individuals can be lost in so short a time.
How far WNS will go in eradicating populations and even whole species remains to be seen, and whether the small number of vesper bats that have been affected so far are representative of the group as a whole is impossible to predict. The reduction of important habitats worldwide – the droughts affecting the tropical rainforests, the impending thawing of permafrost, reduction and pollution of freshwater habitats, sea level rise and the resulting degradation of tropical islands and mangroves – are likely to reduce the resources available to a large percentage of vesper bats and push many more towards and into extinction.
I don’t see it as likely at the moment that we’re witnessing the decline of vesper bats as a whole, but it’s not difficult to imagine a future where but a substantially reduced inventory of species remain.
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)
- Pipistrelles proper: little bats that glide, sing, swarm and lek (vesper bats part XVIII)
- Bird predation, sexual segregation and fission-fusion societies: the amazing noctules (vesper bats part XIX)
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 – –
Blehert, D. S., Hicks, A. C., Behr, M., Meteyer, C. U., Berlowski-Zier, B. M., Buckles, E. L., Coleman, J. T. H., Darling, S. R., Gargas, A., Niver, R., Okoniewski, J. C., Rudd, R. J. & Stone, W. B. 2009. Bat white-nose syndrome: an emerging fungal pathogen? Science 323, 227.
Frick, W. W., Pollock, J. F., Hicks, A. C., Langwig, K. E., Reynolds, D. S., Turner, G. G., Butchkoski, C. M. & Kunz, T. H. 2010. An emerging disease causes regional population collapse of a common North American bat species. Science 329, 679-682.
Tuttle, M. 1979. Status, causes of decline, and management of endangered gray bats. Journal of Wildlife Management 43, 1-17.
Puechmaille, S. J., Verdeyroux, P., Fuller, H., Ar Gouilh, M., Bekaert, M. & Teeling, E. C. 2010. White-nose syndrome fungus (Geomyces destructans) in bat, France.
Emerging Infectious Diseases 2010 Feb doi:10.3201/eid1602.091391.