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next-door nature, urban wildlife, suburban wildlife, barn swallows

The barn swallow is a spectacular aerial acrobat (Photo: Eugene Beckes, Creative Commons license)

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WITNESS astounding tricks of precision flying!

THRILL to the sight of daring aerial capers!

Come one, come ALL!

The FLYING CIRCUS is winging its way to a backyard near YOU!!

 

next-door nature, urban wildlife, suburban wildlife, barn swallowCritics are raving about this summer’s must-see event. Word to the wise, though—in addition to a lawn chair you’ll definitely want to bring some binoculars. That’s because the stars of this air show have an average wingspan of about 12 inches (30 cm). We’re not talking F/A-18 Hornets here, or even a Cessna 152. Think sparrow-sized, not Sparrowhawk.

Barn swallows (Hirundo rustica) epitomize the principle of “form follows function.” Combine a slender fuselage with long, tapered wings and a deeply forked stabilizer (aka “tail”) and you’ve got a bird made to spend the majority of waking life with wheels up. They even wear a uniform appropriate for fly-boys (and girls)—glossy chrome blue above and buff-to-rust below; similar to the colors of a U.S. Air Force Blue Angels jet.

Barn swallows are found far beyond U.S. borders, though.  You might even go so far as to call them jet setters. Six officially recognized subspecies are found in North and South America, Europe, Africa, and Asia. Generally speaking, the species breeds in the Northern Hemisphere (as far north as the Arctic Circle) and takes winter R&R in the Southern Hemisphere. Ornithologists have recorded barn swallows traveling over 7,000 miles (11,000 km) from Europe to southern Africa, and those based in the Americas cover similar distances.

next-door nature, urban wildlife, suburban wildlife, barn swallowWhether cruising inches above land or water or performing barrel rolls, loop-the-loops, spins, and stalls in mid-air, these agile flyers are crowd-pleasers. They aren’t grandstanding, though. A barn swallow’s life consists of more than playing with the physics of flight. Like the post-WWI stunt pilots of the 1920s, they’re trying to make a living.

It takes fuel to fly and the barn swallow go-juice of choice is winged insects—primarily high-octane flies, but also beetles, bees and wasps, next-door nature, urban wildlife, suburban wildlife, barn swallowmoths and butterflies, ants and termites.  Eating on the fly really comes in handy during long missions, including migration. Quenching one’s thirst, bathing, dating, and defending the home territory—they’re all done on the wing.

Historians disagree as to the origin of the term “barnstorming,” but one popular explanation is that pilots would fly through an open barn door and out the other side (they hoped) as a demonstration of their prowess and to drum up joy ride business.  Barn swallows have been known to fly in and out of barns as well—hence the common name. It’s a lot less risky for the birds, though.

Even daredevils like to have a place to call home, a chance to raise a family.  Before permanent man-made structures became commonplace, barn swallows built nests in caves or on the face of cliffs. Long tolerated by humans for reasons  both practical and aesthetic, today only one North American population holds to this tradition, in the Channel Islands off the coast of California; the rest of the fleet hangar in the rafters of open buildings or beneath porches. Bridges, especially those that span water, are particularly popular due to their proximity to crucial building materials.

next-door nature, urban wildlife, suburban wildlife, barn swallowGathering mud by the bill-full, mated pairs make countless supply runs to construct a neat cup or half-cup, depending on the location, then line it with grass, feathers, hair from the livestock living under the same roof, and any other soft, insulating materials they can find.

Once there’s a home base in the crosshairs, the bombardier gets the go-ahead to drop her payload of 3-7 eggs. The pair begin a series of aerial fueling attempts and in about a month’s time they’ve got themself a squadron of next-gen aviators.

Time to put on a show!

next-door nature, urban wildlife, suburban wildlife, barn swallow
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Barn swallows in flight:

Modern day barnstormer performing aerial acrobatics:

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love-earthThis blog, like so many activities that foster support and appreciation of the natural world, is a labor of love. If you’ve enjoyed learning about the creatures who share our built environment, consider becoming an NDN Benefactor with a donation of any amount you’re inspired to give. If you’d like to find a little Next-Door Nature surprise in your inbox just click the Subscribe!  button in the upper right-hand corner of this page and receive notifications of new posts!

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© 2012 Next-Door Nature—no reprints without written permission from the author (I’d love for you to share my work; all you have to do is ask). Thanks to these photographers for making their work available through a Creative Commons license: [from the top] Eugene Beckes (wings tucked; wings open); Julio Mulero (drinking); Dan Wilson Photography (nestlings); Eugene Beckes (swooping); Bill Lynch (muckraking); Mikael Dusenne (parenting); Pat Gaines (missile).

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Mexican free-tailed bat

Bracken Cave, in the Texas Hill Country, is home to the world’s largest colony of Mexican free-tailed bats. (Photo: © Merlin D. Tuttle, Bat Conservation International, http://www.batcon.org. Used with permission)

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When Doppler radar first arrived in the area known affectionately to Texans as The Hill Country, local television station meteorologists were understandably eager to show off the weather forecasting capabilities of their newest toy. Unfortunately, they got off to a less than impressive start. Night after night that summer, evening thunderstorms were forecast but failed to appear. This created distrust within the populace and confusion among the weather men and women. Eventually, someone figured out that Doppler couldn’t tell the difference between a microwave reflected by water droplets in the atmosphere and Mexican free-tailed bats (Tadarida brasiliensis) emerging from nearby Bracken Cave.

How many bats does it take to confuse Doppler radar? About 20 million.

Hundreds of Austin residents and visitors gather at the Congress Avenue Bridge every summer night to observe 1.5 million bats emerging to feed (Photo: © Merlin D. Tuttle, Bat Conservation International, http://www.batcon.org. Used with permission)

Several times in my life, I’ve had the privilege of watching, with barely contained glee, as Austin’s famous Congress Avenue bats poured out of the expansion slots below the bridge deck. With 1.5 million bats in residence, the city is home to the world’s largest urban bat colony. But the Bracken Cave colony dwarfs its city neighbor. It’s the world’s biggest, as well as the greatest known concentration of non-human mammals. Modern Americans will never have a chance to witness hordes of bison churning up the prairie or enormous flocks of passenger pigeons darkening the skies, but Bracken Cave—where it takes 4 hours for all the adult bats to stream out of the cave mouth and drift like smoke over Texas to feed—evokes some sense of what has been lost.

While in Austin a couple of years ago to attend the International Urban Wildlife Management Conference, I finally realized a long-time dream to witness this event with my own eyes. I was not disappointed. Bat Conservation International (BCI) owns the cave and the 697-acre buffer zone that keeps development at bay. The organization, which limits the number of visitors, graciously agreed to lead a group of conference attendees to the property, located near San Antonio.

During a brief orientation we learned that Bracken Cave bats migrate to Texas each spring from their winter home in Mexico, a distance of approximately 1,000 miles. The roof of the cave collapsed at some point in history, forming a perfect amphitheater from which to view the resulting entrance. Members of our group settled in twos and threes to watch, using small boulders as chairs and loveseats while we waited for the day to end and the main event to begin.

Bracken Cave is a maternal colony—no men allowed in this sorority—and soon after the females arrive, each gives birth to a single pup. Mexican free-tailed bat babies are not raised as only children; their mothers park them in a communal nursery set apart from where the adults hang out during the day. With as many as 500 babies per square foot of cave wall, the naked infants generate enough warmth to keep themselves cozy, freeing their mothers to leave each evening to cruise for calories. The downside of this arrangement? When it’s time to feed the offspring, Mom has to find her child somewhere in the mob—a task most human parents would find daunting.

The cave is not a home people would consider sweet. Millions of bats digesting millions of insects from March through October results in an annual deposition of 85 to 100 tons of bat feces, known as guano, on the cave floor. Experts estimate the guano may be 70 feet deep at the very back of the cave (and how one becomes an expert at estimating guano depth is beyond my ability, or desire, to imagine). As part of its stewardship of the site, BCI schedules periodic off-season “mining” of the guano—a practice that goes back to the late 1800s—which is currently sold as organic fertilizer.

As you approach the cave from a staging area near the property entrance, the distinctive, acrid smell of bat waste is hard to miss. Consider, if you dare, what it’s like underground. In winter, when the gals head south of the border to hook up with the guys and have the bat equivalent of a “Girls Gone Wild” experience, the cave is a comfortable 68°F; during the summer months, heat generated by all those bat bodies brings the ambient temperature inside to 108°F. Dermestid beetles are so abundant the floor writhes. The beetles feed primarily on guano, but any infant or injured bat who has the bad luck of falling is swarmed and consumed in minutes. Ammonia gas, a by-product of beetle digestion, fills the cave; levels inside are high enough to be fatal to humans so researchers must wear breathing apparatus to enter when the bats are there.

Personally, this is not the kind of place I’d choose to spend the summer. I lived in Texas for nearly 20 years and I have to say, the heat, humidity, and insect life above ground in July and August is as close to hell as I care to experience.*

Thankfully, during our field trip the air outside the cave was much more refreshing. It was a beautiful, clear, and blessedly temperate May evening, and before too long we began to see movement near the mouth of the cave. This show featured aerial acrobatics that would be the envy of any Blue Angel pilot. Bats were climbing, diving, banking, and stalling, making literally hundreds of mid-course corrections to avoiding collisions, while also attempting to evade the grasping hands of raccoons that gather near the mouth of the cave and the sharp talons of hawks circling above. It’s a dizzying scene, and the bats are both predator and prey.

What began as a small shower of bats quickly turned into a storm, with thousands of leathery wings mimicking the sound of a downpour. As their numbers continued to grow, they swirled and pulsed like a tornado, spinning in seemingly endless circles within the bowl of the sinkhole. Only after I raised my eyes from the dervish before me did I see a dark, smoky trail of bats stretching off beyond the horizon. And still the deluge continued all around us… bats, and more bats, and still more bats.

If, as Doppler radar would have us believe, bats are indistinguishable from raindrops, I’d have been drenched. And singin’, just singin’, in the rain.

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NOTE: Why are these bats called “free-tailed”? Because, unlike many species, the tail is not completely surrounded by a membrane, known at the patagium, that stretches between the animals’ legs—its at least partially “free” (see illustration below). The patagium also stretches between the fingers and connects the front and rear limbs to form the wing.

bat tails

Mexican free-tailed bat (left) and a Townsend’s big-eared bat (right)

*ok, I’ll confess to some hyperbole for the sake of the story. I actually enjoyed living in Texas, although less so during the summer.

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love-earthThis blog, like so many activities that foster support and appreciation of the natural world, is a labor of love. If you’ve enjoyed learning about the creatures who share our built environment, consider becoming an NDN Benefactor with a donation of any amount you’re inspired to give. If you’d like to find a little Next-Door Nature surprise in your inbox just click the Subscribe!  button in the upper right-hand corner of this page and receive notifications of new posts!

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© 2011 Next-Door Nature— no reprints without written permission from the author. Thanks to Bat Conservation International for granting permission to use their photos. The drawings used above are open-source content.

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next-door nature, urban wildlife, fence lizard

Everyone, even fence lizards and other ectothermic creatures, are feeling the heat these days (Photo: Bandelier National Monument, Creative Commons license)

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Temperatures across the southern half of the U.S. are soaring into triple digits, so I was trying to think of creative solutions to beat the heat when it hit me—why not become cold-blooded!

next-door nature, urban wildlife, fox squirrelAlas, my brain must have overheated. Once air conditioning allowed a cooler head to prevail I realized that what seemed like a brilliant idea while baking beneath a blazing sun is absolutely, completely, utterly impossible… and not simply because mammals cannot will themselves to undergo metamorphosis.

You see, technically there’s no such thing as a cold-blooded animal (unless you’re speaking metaphorically about someone who lacks emotion or empathy).  Or a warm-blooded animal, for that matter. Both terms are shorthand for the ways in which body temperature (aka thermophysiology) is controlled in different types of organisms.

Most mammals and birds are classified as endotherms (Greek: endon = within; thermē = heat). For these critters thermoregulation is an inside job, primarily by way of metabolic processes. Under extreme environmental next-door nature, urban wildlife, sunbathersconditions some physical mechanisms come into play, but not solar energy (at least, not directly). If the mercury plummets and the body’s core temperature begins to drop, muscles shiver to create warmth; if the core temperature starts to rise the body perspires to cool via evaporation. No sweat glands? Pant like a dog… or birds. All evidence to the contrary, since humans are mammals, swimsuit-clad sunbathers dozing in rows on a beach or poolside with icy drinks standing at the ready are, in fact, capable of maintaining a relatively constant body temperature.

next-door nature, urban wildlife, gray treefrogWhen an animal’s body temperature is strongly influenced by ambient conditions it’s an ectotherm (Greek: ektós = outside). Fish, amphibians, reptiles, and invertebrates rely on external heat sources to get their juices flowing, especially during the chillier seasons or cooler times of day. That’s why these animals can be seen basking on rocks, roads, and any other warmth-radiating surface. Then, when they can’t stand the heat they get out of the kitchen, retreating into shade, water, or underground to cool off (Sound familiar? We really are more alike than different).

Take-home message: mammals and birds are endotherms; invertebrates, fish, amphibians, and reptiles are ectotherms.

Except when they aren’t.

It’s the exceptions that make the rule, right? Let’s begin with the usual ectotherm suspects. According to one source, 2% of invertebrates are endothermic. Regrettably, the informant failed to name names but, in spite of the fact that spineless animals are not my strong suit, I did managed to chased one down—snails and slugs (Oops, that’s two… and “chased” may be overstating things).  Fish, being vertebrate species, are my regular beat so I can state with certainty that billfish (e.g., sailfish, marlins), tuna (Scombridae), one family of sharks (Lamnidae, including makos and whites), and one species of mackerel (Gasterochisma melampus) are endothermic… at least to some degree. I’ve yet to find a reliable report of an endothermic amphibian, but among the reptiles sea turtles exhibit both ecto- and endothermic traits.

next-door nature, urban wildlife, echidnaMoving along to the endothermic exceptions… Hummingbirds (Trochilidae), swifts (Apodidae), and common poorwills (Phalaenoptilus nuttallii) all experience periods of lower body temperature and metabolic rate; therefore, some biologists argue they have ectothermic traits. Additionally, there are mammals—certain rodents, a couple of lemurs, and many bats—that enter hibernation or estivation in response to low temperatures or drought, respectively. Then there’s the echnidna (Tachyglossidae), a “primitive” mammal from Australia that’s an ectotherm eleven months of the year and an endotherm during the month when it lays its eggs (Yes, eggs. If you like rule-breakers Australia is your Mecca. In the interest of time and space, though, we’ll have to save monotremes for another day).

What I’ve presented above is a fairly simplistic description of thermophysiology.  Why stop there? Because a more thorough treatment would require a good deal of nuance and a complicated discussion of sub-categories, not to mention a stiff drink (the current temperature is 99°F and rising—make mine a frozen margarita).  But since it’s so hot I’ll go ahead and venture past a toe in the water… up to my knees, but no further.

next-door nature, urban wildlife, elephant shrewOne subset of the endotherms are tachymetabolic (Greek: tachy = quick), organisms with a consistent and extremely high metabolic rate. Shrews (Soricidae) are a perfect example—diminutive beings with massive appetites, their metabolic rate is at least five times that of similarly sized ectotherms. Being able to snack non-stop and still rock a bikini probably sounds too good to be true. It is. Finding a constant supply of calories without access to fast food and grocery stores is no picnic. Bradymetabolic (Greek: brady = slow), which could easily be mistaken for bipolar disorder, is no bed of roses either. These organisms swing wildly between a high (when active) and low (when resting) metabolism, usually based on either external temperatures or food availability. (If you think someone else has got it better, rest assured you probably don’t know the whole story.)

As biologists refine our understanding of how bodies work, language evolves and once popular terms like cold-blooded fall from favor. Popular stereotypes suggest otherwise, but scientists are not completely immune to trends. When I was an undergrad, for example, the preferred word for organisms influenced by changes in ambient temperature was poikilotherm (Greek: poikilo = varied, irregular). Although still useful for making distinctions between types of ecotherms, the term is used less frequently now and may be on it the way out.

next-door nature, urban wildlife, crocodilesC’est la vie. Styles change, in both the lab and on the beach (Thankfully. I’m old enough to remember when Speedos were all the rage in men’s swimwear). I’d be willing to bet, though, that most Earthlings won’t give up sun worship any time soon. Chillin’ in a sunbeam feels too good, whether you need it or not (at least as long as there’s a pool nearby).

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Start your day with a little Next-Door Nature—click the “subscribe”  link in the upper right-hand corner of this page and receive notifications of new posts!
© 2012 Next-Door Nature—no reprints without written permission from the author (I’d love for you to share my work. Just ask first.). Thanks to these photographers for making their work available through a Creative Commons license: Bandelier National Monument (sunning fence lizard); Michael V. Flores (fox squirrel cooling down); Nick Papakyriazis (sunbathers); geopungo (gray treefrog); BohemianDolls (elephant shrew); and Jess Loughborough (basking crocodiles).

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next-door nature, urban wildlife, suburban wildlife, barn swallows

The barn swallow is a spectacular aerial acrobat (Photo: Eugene Beckes, Creative Commons license)

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WITNESS astounding tricks of precision flying!

THRILL to the sight of daring aerial capers!

Come one, come ALL!

The Flying Circus is winging its way to a backyard near YOU!!

 

next-door nature, urban wildlife, suburban wildlife, barn swallowCritics are raving about this summer’s must-see event. Word to the wise, though—in addition to a lawn chair you’ll definitely want to bring some binoculars. That’s because the stars of this air show have an average wingspan of about 12 inches (30 cm). We’re not talking F/A-18 Hornets here, or even a Cessna 152. Think sparrow-sized, not Sparrowhawk.

Barn swallows (Hirundo rustica) epitomize the principle of “form follows function.” Combine a slender fuselage with long, tapered wings and a deeply forked stabilizer (aka “tail”) and you’ve got a bird made to spend the majority of waking life with wheels up. They even wear a uniform appropriate for fly-boys (and girls)—glossy chrome blue above and buff-to-rust below; similar to the colors of a U.S. Air Force Blue Angels jet.

Barn swallows are found far beyond U.S. borders, though.  You might even go so far as to call them jet setters. Six officially recognized subspecies are found in North and South America, Europe, Africa, and Asia. Generally speaking, the species breeds in the Northern Hemisphere (as far north as the Arctic Circle) and takes winter R&R in the Southern Hemisphere. Ornithologists have recorded barn swallows traveling over 7,000 miles (11,000 km) from Europe to southern Africa, and those based in the Americas cover similar distances.

next-door nature, urban wildlife, suburban wildlife, barn swallowWhether cruising inches above land or water or performing barrel rolls, loop-the-loops, spins, and stalls in mid-air, these agile flyers are crowd-pleasers. They aren’t grandstanding, though. A barn swallow’s life consists of more than playing with the physics of flight. Like the post-WWI stunt pilots of the 1920s, they’re trying to make a living.

It takes fuel to fly and the barn swallow go-juice of choice is winged insects—primarily high-octane flies, but also beetles, bees and wasps, next-door nature, urban wildlife, suburban wildlife, barn swallowmoths and butterflies, ants and termites.  Eating on the fly really comes in handy during long missions, including migration. Quenching one’s thirst, bathing, dating, and defending the home territory—they’re all done on the wing.

Historians disagree as to the origin of the term “barnstorming,” but one popular explanation is that pilots would fly through an open barn door and out the other side (they hoped) as a demonstration of their prowess and to drum up joy ride business.  Barn swallows have been known to fly in and out of barns as well—hence the common name. It’s a lot less risky for the birds, though.

Even daredevils like to have a place to call home, a chance to raise a family.  Before permanent man-made structures became commonplace, barn swallows built nests in caves or on the face of cliffs. Long tolerated by humans for reasons  both practical and aesthetic, today only one North American population holds to this tradition, in the Channel Islands off the coast of California; the rest of the fleet hangar in the rafters of open buildings or beneath porches. Bridges, especially those that span water, are particularly popular due to their proximity to crucial building materials.

next-door nature, urban wildlife, suburban wildlife, barn swallowGathering mud by the bill-full, mated pairs make countless supply runs to construct a neat cup or half-cup, depending on the location, then line it with grass, feathers, hair from the livestock living under the same roof, and any other soft, insulating materials they can find.

Once there’s a home base in the crosshairs, the bombardier gets the go-ahead to drop her payload of 3-7 eggs. The pair begin a series of aerial fueling attempts and in about a month’s time they’ve got themself a squadron of next-gen aviators.

Time to put on a show!

next-door nature, urban wildlife, suburban wildlife, barn swallow
.There’s nothing quite like finding a little Next-Door Nature in your email inbox—click the “subscribe”  link in the upper right-hand corner of this page and receive notifications of new posts!
© 2012 Next-Door Nature—no reprints without written permission from the author (I’d love for you to share my work; all you have to do is ask). Thanks to these photographers for making their work available through a Creative Commons license: [from the top] Eugene Beckes (wings tucked; wings open); Julio Mulero (drinking); Dan Wilson Photography (nestlings); Eugene Beckes (swooping); Bill Lynch (muckraking); Mikael Dusenne (parenting); Pat Gaines (missile).
Barn swallows in flight:
Modern day barnstormer performing aerial acrobatics:

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wood duckling

Wood ducklings are natural-born paratroopers (Photo: Winnu, Creative Commons license)

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What has webbed feet, waterproof feathers, a broad bill… and nests in a tree? Don’t let that last clue fool you. While it’s true most ducks build their nests on the ground, the wood duck (Aix sponsa) aims a little higher.

wood duck pair by Rick Leche, Creative Commons licenseThis species is easy to recognize, at least as adults. The male is a dandy dabbler, sporting a glossy iridescent green head, a white chin, and a speckled russet cravat. The female’s wardrobe is a bit more subdued, but her large, white teardrop-shaped eye patches are unique among North American ducks.

Wood duck hens prefer to nest in a tree cavity, but they’ll accept a custom-made nesting box if it’s positioned correctly—you know what the Realtors say, “Location, location, location.” After hatching, ducklings spend about 24 hours in the nest while their baby down dries. The young are precocial, meaning they can walk, swim, and feed on their own—but first they have to get out of the tree house. And that first step is an 8–30’ doozy!

Momma flies down to the ground and then calls for her offspring to follow. But the hen has fully developed, fully feathered wings. There’s nothing aerodynamic about a one-day old duckling. Yet, one by one, they use their sharp claws to scramble up from the nest floor to the entrance, balance on the edge, and…. LEAP!

Fluttering useless wing stubs they fall like fluffy stones and land with a thump on their sternums. They shake it off and wait for the rest of their siblings to take the plunge, then the whole family heads off to join Dad at the nearest body of water. Foolhardy as this approach to child-rearing may seem to us, it’s worked very well for generations of tree-nesting ducks.

wood duck hen and ducklings by Ducklover Bonnie, Creative Commons licenseThat is, until they had to share the woods with people. Mother duck may mistake a swimming pool for a pond, and while she can easily clear a tall fence to find wilder waters, her youngsters can’t. However, they’re drawn instinctively to the safety of water. Homeowners who find themselves hosting an impromptu waterfowl pool party should consult with their friendly neighborhood wildlife rehabilitator for advice. Wood ducklings are shy creatures, and the wrong kind of help can send them into a state of shock, or worse.

Delicate? I guess that’s one way to look at it. Who am I to judge, though? I’m not afraid of heights, but if I were a duckling making that jump from nest to terra firma, I’d be in shock before I was halfway down.

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Start your day with a little Next-Door Nature—click the “subscribe”  link in the upper right-hand corner of this page and receive notifications of new posts!
© 2011 Next-Door Nature—no reprints without written permission from the author (I’d love for you to share my work. Just ask first.). Thanks to these photographers for making their work available through a Creative Commons license: Winnu (duckling); Rick Leche (male and female); Ducklover Bonnie (female with ducklings).

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Mexican free-tailed bat

Bracken Cave, in the Texas Hill Country, is home to the world’s largest colony of Mexican free-tailed bats. (Photo: © Merlin D. Tuttle, Bat Conservation International, http://www.batcon.org. Used with permission)

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When Doppler radar first arrived in the area known affectionately to Texans as the Hill Country, the local television station meteorologists were understandably eager to show off the weather forecasting capabilities of their newest toy. Unfortunately, they got off to a less than impressive start. Night after night that summer, evening thunderstorms were forecast but failed to appear. This created distrust within the populace and confusion among the weather men and women. Eventually, someone figured out that Doppler couldn’t tell the difference between a microwave reflected by water droplets in the atmosphere and Mexican free-tailed bats (Tadarida brasiliensis) emerging from nearby Bracken Cave.

How many bats does it take to confuse Doppler radar? About 20 million.

Hundreds of Austin residents and visitors gather at the Congress Avenue Bridge every summer night to observe 1.5 million bats emerging to feed (Photo: © Merlin D. Tuttle, Bat Conservation International, http://www.batcon.org. Used with permission)

Several times in my life, I’ve had the privilege of watching, with barely contained glee, as Austin’s famous Congress Avenue bats poured out of the expansion slots below the bridge deck. With 1.5 million bats in residence, the city is home to the world’s largest urban bat colony. But the Bracken Cave colony dwarfs its city neighbor. It’s the world’s biggest, as well as the greatest known concentration of non-human mammals. Modern Americans will never have a chance to witness hordes of bison churning up the prairie or enormous flocks of passenger pigeons darkening the skies, but Bracken Cave—where it takes 4 hours for all the adult bats to stream out of the cave mouth and drift like smoke over Texas to feed—evokes some sense of what has been lost.

While in Austin last month to attend the International Urban Wildlife Management Conference, I finally realized a long-time dream to witness this event with my own eyes. I was not disappointed. Bat Conservation International (BCI) owns the cave and the 697-acre buffer zone that keeps development at bay. The organization, which limits the number of visitors, graciously agreed to lead a group of conference attendees to the property, located near San Antonio.

During a brief orientation we learned that the Bracken Cave bats migrate to Texas each spring from their winter home in Mexico, a distance of approximately 1,000 miles. The roof of the cave collapsed at some point in history, forming a perfect amphitheater from which to view the resulting entrance. Members of our group settled in twos and threes to watch, using small boulders as chairs and loveseats while we waited for the day to end and the main event to begin.

Bracken Cave is a maternal colony—no men allowed in this sorority—and soon after the females arrive, each gives birth to a single pup. Mexican free-tailed bat babies are not raised as only children; their mothers park them in a communal nursery set apart from where the adults hang out during the day. With as many as 500 babies per square foot of cave wall, the naked infants generate enough warmth to keep themselves cozy, freeing their mothers to leave each evening to cruise for calories. The downside of this arrangement? When it’s time to feed the offspring, Mom has to find her child somewhere in the mob—a task most human parents would find daunting.

The cave is not a home people would consider sweet. Millions of bats digesting millions of insects from March through October results in an annual deposition of 85 to 100 tons of bat feces, known as guano, on the cave floor. Experts estimate the guano may be 70 feet deep at the very back of the cave (and how one becomes an expert at estimating guano depth is beyond my ability, or desire, to imagine). As part of its stewardship of the site, BCI schedules periodic off-season “mining” of the guano—a practice that goes back the late 1800s—which is currently sold as organic fertilizer.

As you approach the cave from a staging area near the property entrance, the distinctive, acrid smell of bat waste is hard to miss. Consider, if you dare, what it’s like underground. In winter, when the gals head south of the border to hook up with the guys and have the bat equivalent of a “Girls Gone Wild” experience, the cave is a comfortable 68°F; during the summer months, heat generated by all those bat bodies brings the ambient temperature inside to 108°F. Dermestid beetles are so abundant the floor writhes. The beetles feed primarily on guano, but any infant or injured bat who has the bad luck of falling is swarmed and consumed in minutes. Ammonia gas, a by-product of beetle digestion, fills the cave; levels inside are high enough to be fatal to humans so researchers must wear breathing apparatus to enter when the bats are there.

Personally, this is not the kind of place I’d choose to spend the summer. I lived in Texas for nearly 20 years, and I have to say, the heat, humidity, and insect life above ground in July and August is as close to hell as I care to experience.

Thankfully, during our field trip the air outside the cave was much more refreshing. It was a beautiful, clear, and blessedly temperate May evening, and before too long we began to see movement near the mouth of the cave. This show featured aerial acrobatics that would be the envy of any Blue Angel pilot. Bats were climbing, diving, banking, and stalling, making literally hundreds of mid-course corrections to avoiding collisions, while also attempting to evade the grasping hands of raccoons that gather near the mouth of the cave and the sharp talons of hawks circling above. It’s a dizzying scene, and the bats are both predator and prey.

What began as a small shower of bats quickly turned into a storm, with thousands of leathery wings mimicking the sound of a downpour. As their numbers continued to grow, they swirled and pulsed like a tornado, spinning in seemingly endless circles within the bowl of the sinkhole. Only after I raised my eyes from the dervish before me did I see a dark, smoky trail of bats stretching off beyond the horizon. And still the deluge continued all around us… bats, and more bats, and still more bats.

If, as Doppler radar would have us believe, bats were indistinguishable from raindrops, I’d have been drenched. And singin’, just singin’, in the rain.

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NOTE: Why are these bats called “free-tailed”? Because, unlike many species, the tail is not completely surrounded by a membrane, known at the patagium, that stretches between the animals’ legs—its at least partially “free” (see illustration below). The patagium also stretches between the fingers and connects the front and rear limbs to form the wing.

bat tails

Mexican free-tailed bat (left) and a Townsend’s big-eared bat (right)

© 2011 Next-Door Nature— no reprints without written permission from the author. Thanks to Bat Conservation International for granting permission to use their photos. The drawings used above are open-source content.

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wood duckling

Wood ducklings are natural-born paratroopers (Photo: Winnu, Creative Commons license)

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What has webbed feet, waterproof feathers, a broad bill… and nests in a tree? Don’t let that last clue fool you. While it’s true most ducks build their nests on the ground, the wood duck (Aix sponsa) aims a little higher.

wood duck pairThis species is easy to recognize, at least as adults. The male is a dandy dabbler, sporting a glossy iridescent green head, a white chin, and a speckled russet cravat. The female’s wardrobe is a bit more subdued, but her large, white teardrop-shaped eye patches are unique among North American ducks.

Wood duck hens prefer to nest in a tree cavity, but they’ll accept a custom-made nesting box if it’s positioned correctly—you know what the Realtors say, “Location, location, location.” After hatching, ducklings spend about 24 hours in the nest while their baby down dries. The young are precocial, meaning they can walk, swim, and feed on their own—but first they have to get out of the tree house. And that first step is an 8–30’ doozy!

Momma flies down to the ground and then calls for her offspring to follow. But the hen has fully developed, fully feathered wings. There’s nothing aerodynamic about a one-day old duckling. Yet, one by one, they use their sharp claws to scramble up from the nest floor to the entrance, balance on the edge, and…. LEAP!

Fluttering useless wing stubs they fall like fluffy stones and land with a thump on their sternums. They shake it off and wait for the rest of their siblings to take the plunge, then the whole family heads off to join Dad at the nearest body of water. Foolhardy as this approach to child-rearing may seem to us, it’s worked very well for generations of tree-nesting ducks.

That is, until they had to share the woods with people. Mother duck may mistake a swimming pool for a pond, and while she can easily clear a tall fence to find wilder waters, her youngsters can’t. However, they’re drawn instinctively to the safety of water. Homeowners who find themselves hosting an impromptu waterfowl pool party should consult with their friendly neighborhood wildlife rehabilitator for advice. Wood ducklings are shy creatures, and the wrong kind of help can send them into a state of shock, or worse.

Delicate? I guess that’s one way to look at it. Who am I to judge, though? I’m not afraid of heights, but if I were a duckling making that jump from nest to terra firma, I’d be in shock before I was halfway down.


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© 2011 Next-Door Nature— no reprints without written permission from the author. Thanks to Rick Leche for using the Creative Commons license for his beautiful photograph of the wood duck drake and hen.

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