Bats In Our Attic

Note to visitors:  This post began life in the Canadian maritimes, where everything is right and true.  It took two months to write, and one of its sub-themes (waiting for October) may seem odd given that it now is October.  The reason for the sluggish pace is that the post contains science, lots of it, and my editors and I are not scientists.  We labored over source material so as to avoid careless extrapolations from same, and we have peppered in source-links so that you can weigh your understandings against our own.  All in all, we feel our findings are spot on.

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My wife and I have bats in our attic, but we are advised to wait until October to deal with them.  Our attic is cold by then and the bats will fly south, a move hastened by a vanishing insect food source.  Many bugs die of old age, predation, autumn frosts; plus, something about mating does them in.  A number of adult moths die after mating and male mosquitoes expire as well, leaving surviving partners and larvae to carry on in a suspended animation called diapause.

With cold quarters and insufficient food, the bats head out.

That bat colonies would pack up and zig toward warmer climes is something to consider.  How far south? I'm wondering.  Perhaps not very: some bats may find warmer hibernation roosts in caves or shelters nearby, but I'm pulling for a longer migration* –– to South Beach, say, or the Plantation House on the Grenadine island of Mustique, where weekly winter rates (up to 10 human guests) are $45,000.  *(Migrating bats are known to take music along, especially on longer trips: click on playlist to listen to their traveling music.)

They are artful fliers, neither linear
in their migratory flight paths, nor as disciplined as geese are when shooting north to south.  By nature circuitous, bats are air surfers curlicueing along.  It's hard to imagine their having a leader or showing interest in, much less maintaining, a vee-formation.  And were they able to even manage an extensive southbound trip, it would doubtless include roundabout off-routes.

Which is to say these bats are all over the place.  But that turns out to be a good thing: you will not as a rule find them wearing uniforms, giving or taking orders, impressed by religious or political rigidities, voting in lockstep regimen.  They are not Republicans.

Now the bats in our attic are of the suborder Microchiroptera, probably of the species Myotis Lucifugus, Little Brown Bat.  They look like winged mice, which they are not, being their own mammalian entity.

Little Brown Bat

 (Suborder Microchiroptera)
(Credit: NHPTV)

Microchiroptera number about seventy percent of all bats and are the larger of two suborders. Microbats prefer eating insects, but some species eat mice, frogs, lizards, blood, fish, spiders, scorpions, fruit, flowers.  They have small eyes and poor eyesight, but big ears and echolocation with which to orient and hunt.  Their echolocation is a complex bat-sonar whereby they match outgoing ultrasonic pulses against returning echoes, then "analyze" this data, factoring in their own speed as well as the motion and location of their prey.  This has something to do with the Doppler effect and it is no small tribute to Microbats that they understand this stuff.

Seychelles Fruit Bat
(Suborder Megachiroptera)
(Credit: Wikimedia Commons)

These Microbats have cousins in a smaller suborder, Megachiroptera.  The Megabats are generally bigger, with larger eyes, smaller ears, a keen sense of smell, and no echolocation.  Whereas Microbats are largely insectivores, Megabats are largely frugivores, eating fruit, pollen, nectar, and relying on vision and smell to locate food.  Whereas Microbats –– using echolocation –– can roost in caves, wells, and other dark spaces, Megabats tend to roost in the open in trees, traveling by night to forage in rainforest canopies and other fruited and flowered sites.

And they are especially fortunate to live in the Tropics; the Old World tropics, that is, in places like Africa, Indomalaya, Australasia. 

They do not hibernate and, given sufficient food availability, they have less need for migration.  In turn, this stationary lifestyle has given rise to
a perception that Megabits are indolent and profligate: staying home, hanging out, listening to music,* binging on fruit, and tossing down fermented nectar –– which they seem not to hold well since they appear listless and pie-eyed. That they lack echolocation and thus are prone to fly into things only adds to this impression.  The truth is, we have no evidence to support this perception of profligate Megabits. There is, in fact, a dearth of any data regarding Megabats and ethanol consumption.  *(Megabats are partial to "sweet"-songs: click on playlist to listen.)

However, there is good science about the alcohol consumption of fruit-eating Microbats (recall that some Microbats eat fruit and flowers).  To wit, Canadian researchers at the University of Western Ontario and the University of Regina fed ethanol spiked sugar-water to a group of fruit-eating Microbats, paired this group with a control group fed only sugar-water, then ran both groups through an obstacle course.  The researchers discovered no difference in flight behavior or echolocation performance between test and control groups.

The Microbats seem to hold their liquor.

To partly visualize this, consider the Jamaican Fruit-eating Bat (one of the species researched).  It likes figs; and fermented figs would in situ presumably yield a mild fig schnapps or eau de vie.  Yet based on the science, the Jamaican bat performs admirably in the wild, finding food sources without bumping into things.  (See Drinking and Flying: Does Alcohol Consumption Affect the Flight and Echolocation Performance of Phyllostomid Bats?)

Inasmuch as the Canadian researchers used echolocation as an outcome measure, they necessarily studied the echolocating Microbats; in particular, the Phyllostomidae, or New World Leaf-nosed Bats.  So the dearth of research into the drinking habits of Megabits may be partly explained by the research difficulty in finding an outcome measure as reliably elegant as echolocation performance.

Also, what if Megabats only appear to be but are not numb on nectar-juice.  Might there be an alternate causation for their seeming stupor? My editors and I believe there is.  Our hypothesis, grounded in empirical observation, is this –– that Megabats are not sauced but reminiscing wistfully about their Eocene-epoch salad days, a time 56 to 34 million years ago when Earth's tropical zones extended to 45° north, when their world was sultry and roomy.  Megabats are sunk in reverie, not their cups.

Come again? you're thinking ... Eocene what?

Well, the Eocene epoch was a balmy greenhouse period which hosted the first mammals.  The early Eocene in particular was rather toasty, with warm seas and temperate forests extending to the poles.  The oldest known bat fossils date to this period, 52.5 million years ago. Were we to imagine fancifully that today's geography is the same as that of 52.5 million years ago, then a 45° north latitude would designate a tropical upstate New York just south of its border with Quebec.  As regards cushy climate and habitat, the Eocene amounts to a bat-paradise lost.  (I must digress at this point; the Eocene epoch and its wonders merit elaboration.)

Paleogeographical Detour –– Part I:

You can't fault Megabats their nostalgia for the Eocene, even if it should turn out that they've been dipping into the schnapps.  This bat-friendly Eocene was an extraordinary time, ushered in by an abrupt global warming event called the Paleocene-Eocene Thermal Maximum (PETM).  How abrupt?  Sea surface temperatures rose 5° to 8° Celsius (9° to 14° Fahrenheit) over a few thousand years, a bat-wink in a geological eye; and global atmospheric temperatures rose 6° C (11° F) over 20,000 years.  In the high arctic, you could have swum in 23° C (73° F) waters at the North Pole, though likely you'd have opted not to since large reptiles might have joined you.  There were alligators in the waters off Ellesmere Island and crocodiles off Greenland. 

The PETM occurred 55.8 million years ago at the boundary of the Paleocene and Eocene epochs, this greenhouse transition lasting ~170,000 years.  The Eocene epoch lasted 22 million years overall, with a gradual cooling as Antarctica separated from Australia and South America, opening a deep channel and resulting circum-antarctic current.  But even as the Eocene cooled, it nonetheless remained warm, being succeeded in turn by the cooler Oligocene epoch.  (See American Museum of Natural History for a useful video on the PETM.)

So what occurred at this Paleocene-Eocene boundary?

     This event happened at the end of a ten million year period
     of time known as the Paleocene.  The [CO₂] gas release was
     initiated by an intense period of volcanic seafloor activity that
     stretched and thinned the seabed; forcing the American and
     Eurasian tectonic plates to spread further apart.

     The North Atlantic had a violent birth; volcanic magma and
     superheated water flowed upwards through fissures in the
     earth's crust; to first meet a vast store of hydrocarbon rich
     sediments in seabed basins, then sheets of methane
     hydrates on the seafloor of the continental margins.  There
     was volcanic activity on the surrounding land masses too. 
     Flood basalts from this time are still widely exposed on the
     Faeroe Islands, Greenland and Baffin Island; whilst Iceland
     remains a volcanically 'hot spot' to this day.

     For over 10,000 years the combusted methane from volcanism,
     organic mudstones and methane hydrates combined with
     oxygen in the ocean to become CO_2, increasing the ocean’s
     acidity and quadrupling CO₂ concentrations in the atmosphere. 
     (Excerpted from The Paleocene Eocene Thermal Maximum.)

    Or put more simply:

     What unleashed the PETM is unclear.  Most fingers of blame
     point to volcanic eruptions that disgorged gigatonnes of carbon
     dioxide, or coastal reservoirs of methane gas, sealed by icy soil,
     that were breached by warmer temperatures or receding seas.

     (Excerpted from Global Warming 55 Million Years Ago Shifted
     Ocean Currents.)

Note the attention given methane, a more potent heat-trapping gas than carbon dioxide.  Note also that stores of methane abide in undersea clathrates, solid compounds in which methane molecules are bound within the crystal structure of water molecules.  These clathrates:

     ... may make up a significant portion of total fossil carbon reserves, 
     including coal and oil.  Current best guesses suggest that maybe       
     500 to 2000 gigatonnes of carbon may be stored as methane        
     clathrates (5-20% of total estimated reserves).  Some estimates       
     are as high as 10,000 gigatonnes.  They occur mainly on the      
     continental shelf where the water is relatively cold, [where] there      
     is sufficient pressure and enough organic material to keep the      
     methane-producing bacteria happy.  Most importantly, clathrates
     can be explosively unstable if the temperature increases or the      
     pressure decreases––which can happen as a function of climate
     change, tectonic uplift or undersea landslides.
     (Excerpted from NASA article, Methane: A Scientific Journey 
     From Obscurity to Climate Super-Stardom.)

The flatulence of cows is only a
small portion of cows' methane
release.  Cows also burp methane,
due to the physiology of their 
digestive systems.  
(Credit: Wikipedia.)

Now when methane clathrates do release gas into the atmosphere, it is termed a methane burp in the nomenclature of oceanography and climatology.  Interestingly, human flatus often (but not always) contains methane,* yet a different term applies to human gas emissions –– such that while coastal seafloors burp, humans fart.  The reason for this disparate terminology traces to ruminant biology, and the fact that sheep and cattle burp methane as a digestive function safeguarding against bloat.  By analogy, since seafloor methane is emitted from the top or "mouth" of its sedimentary crust, it is said to be burped.  *(Readers wishing to pursue how to determine methane's presence in human flatus are referred to What is the Chemical Composition of Farts? by Anne Marie Helmenstine, Ph.D.)

Let's return to the above NASA quotation about clathrates, the one with that troubling phrase "explosively unstable."  Hmm, that can't be good –– especially when we consider our slippery congress and its disregard of environmental safeguards and greehouse-gas emissions, also when we recall the massive amounts of carbon dioxide we pump into the ecosphere.

Here is Prof. Lee R. Kump of Pennsylania State University, commenting on research funded by The National Science Foundation, Worldwide Universities Network, and Pennsylvania State University: 

     Rather than the 20,000 years of the PETM which is long enough
     for ecological systems to adapt, carbon is now being released into
     the atmosphere at a rate 10 times faster ... It is possible that this
     is faster than ecosystems can adapt. 

I'll say –– and perhaps faster than we know, given those oily hands at the congressional helm.

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Part II:

Paleographic Reconstruction of
Middle Eocene Earth (50.2 Million 
Years Ago) (Credit: C.R. Scotese, 
Atlas of Earth History)

It is worth adding a visual aid to this Eocene geography of 52.5 million years ago, a geography which can only be known via paleogeographic reconstruction.  The adjacent map shows continents to already have been in their present positions (sort of), and you might compare this Paleomap with the map of modern Earth below it.
 

Modern Earth

(Credit: worldatlas)

Mind you, North America looks squishy in the Paleomap; the Atlantic Ocean, pinched.  Antarctica is still connected to South America and seems a ferry-ride away from Australia.  Meanwhile, chunks of Europe, Asia, the Middle East are under water.  And obviously there could have been no actual Eocene New York, much less a New York-Quebec border.  Place-names such as North America and Antarctica are paleomap retrofits to benefit us moderns.

That said, I will now speculate (hesitantly) about the possibility that Quebec, however improbably, did exist in the Eocene.  Recent geological evidence suggests the startling discovery of fossilized Poutine from drill cores in the central Arctic Ocean –– within 55 million year old sedimentary samples.

Poutine
(Credit: Wikimedia Commons)

Poutine is the justly celebrated Québécoise dish, comprising at a minimum an amalgam of French fries, brown gravy, and fresh cheddar cheese curds.  An immeasurably delicious dish, it is robust and enjoys great staying-power.  And where there is Poutine, there is (or was) a Quebecer* –– although what he or she was doing in the high Eocene Arctic is anyone's guess.

   Les Colons Canadiens:
   La Bolduc

*(For a musical salute to much later settlers, click on Mary Bolduc's 1936 "Les Colons Canadiens.")

Now that a poutine-like compound could be found amidst an Eocene sedimentary matrix of aquatic microorganisms, this is baffling. Certainly the age of these samples is not in question, it is Eocene sedimentary rock.  And chronometric dating of its composition reveals mineralization anomalies which intrigue.  Specifically, mineralogical ratios of potassium, phosphate, and magnesium correlate proportionally with those for potato starch, while ratios of calcium, phosphorus, and sodium are similarly proportionate with cheddar cheese profiles –– both potato and cheese being central properties of Poutine.  

But since suggestive data is not factual data, this putative Eocene Poutine will surely be analysed for years to come.  Should the compound prove to be Poutine, the scientific ramifications will quake established tenets in both hard and social sciences: paleogeology and paleoecology, paleoanthropology and history of religion, paleoagronomy and primitive animal husbandry.  At present, though, we must be patient and await clarity.  (My layout editor, Todd, is not waiting.  He has already submitted a monograph, Mineralogical markers for Poutine in Paleocene-Eocene thermal maximum sediments of the Arctic Ocean, to the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.  And he is positively squirrelly in anticipation of a response.)

Ultimately, the larger point of this digression is that what seems reliably permanent may not be.  In the fullness or geological brevity of time, our planet's geography, climate, ecosystem can change utterly.  It has happened before, it appears to be happening now. Eocene poutine may turn out to be an unconfirmable hypothesis, too sketchy, even dodgy –– but global warming isn't.  (Click on playlist for suitable eco-music.)  (End of digression.)

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There are some 2,400 species of bats, and while insectivores and frugivores comprise the majority, there are nonetheless outlier species: blood eaters, meat eaters, fish eaters.  Among these, a small percentage of blood-eating Microbats has taken on outsized cultural influence, the vampire bats.

Common Vampire Bat

 (Credit:Wikimedia Commons)

There are three species of vampire bats, all located in Central and South America. They tend to feed on sleeping livestock, but bites on humans can occur when farm-workers are sleeping in windowless shelters, or in the open.  From the bats' viewpoint, a human is just another warm-blooded sleeping mammal.  Moreover, the target of the bite on a human is likely the capillary-rich big toe –– not the neck of hollywood legend.  And as for its approach, the vampire bat typically walks up to its victim, bites, and then laps its meal.*  This differs from the mythic creature that swoops out of the darkness to suck at an exposed neck.  Plus, it should also be said that lapping is not sucking; lapping seems nicer, vampire bats are like cats.

   Blood Bank:
   Bon Iver

*(These blood-lappers have small music libraries –– containing one song actually, "Blood Bank" by Bon Iver –– which they play over and over.)

Yet vampires can transmit disease to livestock, and their wounds can be a site for opportunistic infections in younger animals.  And farmers in turn may fail to discriminate between vampire bat roosts and the vast majority of "innocent" bats.  Fear of rabies and safeguarding of herds has consequently put all bats at risk as ranchers and townspeople take retaliatory and preventive measures.  (See Vampires: The Real Story, BATS Magazine, Vol. 9, No. 1, for a useful article on vampire bats.)

Regrettably, ignorance and superstition are not confined to Central and South America, and attacks on bats and extinctions of some species are worldwide.  In addition to which, there are other human activities harmful to bats:  deforestation, which removes roosts and destroys fruit-bearing, insect-attracting plants; agricultural pesticides, which bats ingest via contaminated water sources and sprayed insect populations; and hunting of bats as a source of bushmeat in West Africa, Asia, Pacific and Western Indian Ocean islands.  Moreover, the website Bat Conservation International describes how sensible safety, health, or environmental initiatives can inadvertently harm bats: The closing of caves and abandoned mines can remove necessary habitats; wind-farming turbines, intended to reduce reliance on fossil fuels, unintentionally kill bats and birds.

Finally, there is an implacable fungal infection, white-nose syndrome, afflicting several species of bats in the northeastern United States and Canada -–– and over a million have died (see U.S. Fish & Wildlife Service, or U.S. Geological Survey).  Despite its name, white-nose syndrome is actually a disease of bats' wings:

     ... the real killer appears to be the way the infection attacks wings.
     The fungus causes enough irritation of the paper-thin skin between
     the long digits to rouse bats from hibernation, which in turn boosts
     their metabolism and burns critical fat reserves, making it nearly
     impossible for them to survive the cold months.  Those bats that do
     manage to winter through emerge with wings so ravaged they look
     moth-eaten, which limits the aerial acrobatics that all bats need to
     hunt and lowers the chances that females will put on enough weight
     to nurse pups.
     (Ted Genoways, The Man Who Loves Bats, onearth, 33: 3, p. 48,
     2001.)

This is doubly sad in that bats mean no harm, perform good acts, are already endangered, and are distinctly interesting:

• Bats eat insects.  This does more than reduce bug bites on a summer's evening, there are commercial advantages as well.  Bats control insect populations destructive to farming, thereby increasing crop yield and revenue, promoting less use of pesticides, and reducing the fouling of groundwater and streams.  
• Mexican Free-tailed Bats have been tracked by Doppler radar flying at 10,000 feet.  In south-central Texas alone, these bats are thought to kill 1,000 tons of insects on any given summer night.  Add in the Free-tails from Oklahoma, New Mexico, and Arizona and you have a significant insect-averse fighting force.
• The majority of bats possess echolocation (and they seldom actually crash into you).   
• Bat guano is a nutrient rich fertilizer, as readers of Ian Fleming's 1958 novel Dr. No may recall.  
• Bats pollenate flowers and disperse fruit seeds.  
• A trial of a drug for stroke victims is underway in over 40 hospitals in the United Kingdom.  Derived from Vampire Bat saliva, the drug thins blood and dissolves blood clots in the brain. 
• Bats do like the dusk to dawn hours, and they do seem to lurk in the shadows, but they are not out to get you.  Also, while lovers of night, bats are not fans of moonlit nights and reduce their foraging on bright nights.
• Roosting bats, winding down after a night's hunt or actually hibernating, enjoy slow to mid-tempo background music. They like the old stuff* –– standards, jazz, R&B, Doo-wop –– as it's familiar and reassuring to their paralimbic systems.  Not surprisingly they prefer "night" songs, even those with "moonlight" themes.

         *(Click on playlist to listen to

          some of these chill-out songs.

          They span a forty year period,

          beginning with two 1931

          selections, Ruth Etting's

          "Shine On, Harvest Moon” and

          Bing Crosby’s “When The Blue

          Of The Night [Meets The Gold

          Of The Day],” to Bill Withers'

          1971 "Ain't No Sunshine.”)

• Bats are the only true flying mammals, unlike the misnamed "flying squirrels," for example, which are merely gliders. 
• Their wings are taut membranes between mammalian finger-bones, and their flying is something like a furious flapping-clapping.  A small claw protruding from their "thumbs" aids in grasping objects.  (Since we too are mammals, imagine standing and holding your arms at your sides; now imagine your hands are webbed and that webbing connects your arms to your sides; now imagine you are flapping your "wings" and "swimming"*  through the air.)  *(This apt metaphor is not mine but borrowed from the HowStuffWorks website.) 
• The Kitti's Hog-nosed Bat vies with the Etruscan Shrew for being the smallest mammal in the world. 
• Apart from polar regions and some isolated islands, bats are found everywhere.
• Bats are social animals.  Members of bat colonies engage in cooperative foraging, using group signature screech-calls to communicate.  They also demonstrate babysitting, grooming, and defense of others among the same group. This capacity for social-support networking is the origin for the phrase "going to bat for."
• They are great conversationalists, their calls being classified by ecologists at the University of Kaiserslautern into four types: mutual recognition, mate attraction, aggression, distress.  So ... kinship, love, hostility, suffering; these seem to be on the agenda for bats, and not unlike the concerns of the rest of us mammals.  Anyway, this chatty conversational style has given rise to the phrase "to bat something about."
• Bats' erratic flight pattern has occasioned the pejoratives "bats" and "batty," also the phrase "having bats in one's belfry," as monikers for mental disorder.  This is unfair to bats as it implies that linear thinking (so often leaden and unimaginative) is preferable to spontaneous, off-center, associative thinking.  (The negative terms "dingbat" and "wing nut" would appear to be etymological cousins of these bat-related epithets.) 
• Bat eyelashes, such as they are, are insufficient for flirtations.  Bats do not "bat their lashes" seductively.  They are straightforward in their affections, true-blue in their attachments.
• The phrase "blind as a bat" is misleading.  It is true that Megabats enjoy better eyesight than Microbats, but Microbats are not blind and their low-light vision is acute.  
• Unluckily, some bats (usually Microbats) have an unflattering grimace which can elicit recoil in humans.  But this bat-grimace need not indicate pained disapproval or disgust.  In the case of Microbats, it reflects the furrowed cerebral intensity which inevitably accompanies echolocation, an intensity augmented by those beady eyes and big ears.  As for the larger, big-eyed, small-eared Megabats, they just seem warmer and fuzzier to begin with. Fewer people find them off-putting, and the average "cute" bat is likely a Megabat. 
• We are all currently living in the 2011-2012 United Nations' International Year of the Bat.

Still, in spite of these many positives and singularities –– and returning to the issue of bat-occupancy in our attic –– we are keeping the attic door shut in deference to unwary house guests.

Plus, you don't really want bats flying around your house.  Aside from startling unsuspecting guests, bats can make you sick.  Their guano
can carry fungal spores which if inhaled can cause histoplasmosis, a potentially fatal respiratory infection.  Also, the very occasional bat may carry rabies, a concern to be tempered by the fact that only 0.5% of bats are rabid (in regions endemic for rabies).  And with the CDC citing only 17 cases of bat-borne rabies in the United States between 1996 – 2007, we should be cautious but not hysterical in our dealings with bats.

For the most part then, bats are helpful to have around, just not in your house.

Attic Decontamination
(Credit: aaanimalcontrol.com)

So my wife and I will wait for October, trust that the bats fly south, and hope that they're spared the white-nose syndrome.  Then we'll seal up their access points in the attic dormer and have a trained professional clean up the guano.  The trained professional will look something like this guy.

And then we'll sit down with friends, eat a big pot of Poutine, and drink a health to Todd ... who, even as we tuck in, will be winging his way over the Pacific to Beijing.

Unidentified Man Making Poutine