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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).
wildlife and roads, wildlife watching, wildlife habitat

Roads are both a blessing and a curse for wildlife (Photo: Colleen Greene, Creative Commons license)

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Ever dreamed of going on a safari? Then fasten your seat belt, start the engine, and hit the road. Any road. I’ll bet you dollars to donuts—take the time to look and you’ll spy enough wildlife to satisfy, Bwana.

Sure, some of the creatures will be easier to spot than others… for the simple reason they’re no longer moving.  But I’m not proposing a road-kill road-trip. Trust me, the city streets, shady neighborhood boulevards, highways and byways offer plenty of opportunities for wildlife watching. Naturally, the species on display depend on the size of the road, its location, the season, time of day, and the speed limit.

wildlife and roads, vultures, wildlife watchingLet’s say your motoring down a divided highway, a conduit to and through the all-American suburbs. The big stuff (aka megafauna), such as deer, elk, moose, bears, and even coyotes, can be seen at 65+ mph (although not always in time to either admire or avoid them). Certain birds of prey, red-tailed hawks in particular, can be seen at both speed and distance due to their habit of hanging out high on handy utility poles to scout for snacks. Anything more petite will be visible only if it’s on the shoulder or trying to cross the road. Scavengers looking for a free lunch can be seen out on the open road day (crows, ravens, vultures) and night (opossums, coyotes). That meal ticket can quickly turn the diner into dinner for someone else… and so on.

wildlife and roads, wildlife watching, groundhogBeyond mowed blacktop borders, in the woods and taller grasses, you’ll find rabbits, foxes, raccoons, skunks, and groundhogs. Based on my own non-scientific observation, to improve your chances of seeing these meso– (medium-sized) species as well as small but brightly colored male songbirds in situ you’ll have to ease up on the gas pedal and let the speedometer drop to 35-45 mph, tops.

A bicycle (or even a horse if you have access to one) would probably set the right pace for a rider to notice mice and voles, lizards, turtles, frogs and toads, as well as female songbirds (who tend to have less flashy wardrobes than their ready-for-the-disco menfolk). The truly diminutive critters—insects, spiders, snails and slugs—are hard to spot at more than arm’s length so it’s best to set off on foot and plan for a leisurely pace if spineless quarry is your goal.  A general rule: the slower you go, the more you’ll see—that’s what makes the backroads more appealing for this kind of trip than a superhighway.

In poetry, novels, song, and cinema people often speak of the allure and romance of roads—the ones that calls us, the ones less traveled, the ones that go on forever, choosing between high ones and low ones. Wild animals rarely have access to books and mp3 players and RedBox kiosks, though, and I’ve never found them to be all that interested in popular culture… so what’s the attraction?

To build a road through a previously undeveloped area, the first thing that happens is clearing a swath of the existing plant community, be that trees and shrubs or grasses or cacti. Once the project is completed (or even while it’s still in progress) new plants begin to colonize the bare soil, creating a plant community that’s different from the surrounding landscape along with an edge where new and old meet.  Disturbing the soil stimulates the germination of seeds that may have sat dormant for a long time waiting for the right conditions. Soil may be brought in from somewhere else as part of the construction process along with seeds from plants that are completely novel in this setting.

wildlife and roads, wildlife watching, wildlife habitatSince the plants predict what kind of animals will be found in any ecosystem, the new habitat creates opportunities certain wildlife species will exploit… but in most cases it won’t be the species that were living happily in the pre-construction habitat. Edge species will colonize the area, often using the right-of-way as a travel corridor before and after the road is completed. Some organisms will hitchhike to their new home on and in the bodies of larger animals or even motor vehicles. Birds, bats, and flying insects will drop in from above. Wild things are always jockeying for space and there’s no such thing as a vacant lot in nature—at least, not for long.

wildlife and roads, wildlife watching, pronghornMake no mistake—roads are a significant cause of habitat loss and their presence is detrimental to many types of wildlife. For others, though, the resulting edge provides exactly what they need to thrive. This includes our most familiar next-door nature species. In fact, the reason blue jays, robins, white-tailed deer and other edge-loving species are so common in human communities is because Homo sapiens is also an edge-loving species. Our roads are simply one very conspicuous example of that fact.

The natural world is never static; it’s always in flux and each day there are new winners and losers.  Are roads good or bad for wildlife? It depends on the species. But there’s no doubt they are a boon for wildlife watchers.

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Life is better with 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: Colleen Greene (black bear); e_monk (black vulture); Matt Reinbold (groundhog); MoDOT Photos (edge habitat); Allan Harris (pronghorn).

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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