A scientists’ work is never done.
That’s because there’s always another layer to peel away, another stone to turn, another angle from which to view the situation. Case in point—nearly 200 years ago, Charles Darwin made the connection between the size and shape of a finch’s beak and the availability of the seeds they eat; to this very day, no one has been able to produce evidence that undermines his observation and the conclusions he drew from them.
But what if there’s more to a beak than meets the eye?
That’s the question raised by Russell Greenberg of the Smithsonian Conservation Biology Institute. His theory—that beak size may also be an adaptation to temperature regulation and water conservation—has been bolstered by data from two recently published studies. [Data collected, in part, by a newly minted PhD named Ray Danner. Ray just happens to be a member of my own adopted extended family, and if that name sounds vaguely familiar… well, regular NDN readers may remember that not too long ago I was bragging about another member of this ornithological power couple, Ray’s wife, Dr. Julie Danner.]
Some years back, Greenberg noticed a difference in size between the beaks of sparrows living in salt marshes and those of sparrows settled just a kilometer or two further inland. Then a paper published in 2009 reported toco toucans (Ramphastos toco) may lose as much as 60% of their body heat through their long bills, based on thermal imaging and similar to the role played by the large ears of both elephants (Elephantidae) and jackrabbits (Lepus spp.). While many ecologists assumed toucans were a special case, Greenberg wondered—might other birds have evolved larger or smaller beaks to discharge or conserve heat as well?
He chose to test his hypothesis by applying thermal imaging to a subject with a much less prominent proboscis—the song sparrow (Melospiza melodia). Native to North America, everything about these feathered minstrels is miniature compared to their South American kin. The toucan weighs in at 1-2 pounds (the large bill doesn’t actually tip the scale as much as you might think since it’s mostly hollow) while at 0.4—1.9 ounces the song sparrow is definitely a featherweight.
In the first study, two subspecies were examined. On average, the beak of an Atlantic song sparrow was found to have 17% more surface area than that of the eastern song sparrow, although both birds have similarly sized bodies. Based on the Greenberg team’s calculations, the Atlantic sparrow loses 33% more heat than it’s inland neighbor. The finding suggests beaks may play a role in thermoregulation for a wide variety of bird species.
The ability to stay cool when the ambient temperature rises is critical to survival, but how one gets rid of the excess heat is just as important. Birds don’t sweat—they pant… and lose not just heat but water in the process. This summer, residents across the U.S. have been reminded just what a precious resource water can be, and never more so than for all the creatures without easy access to a faucet. Greenberg and his colleagues suggest that a bird’s beak can function like a radiator, releasing heat without losing water. The Atlantic sparrow’s larger bill saves the bird about 8% more water than the smaller beaked eastern sparrow. That may not sound like much but during a hot, dry summer it could be a significant survival advantage.
The second study examined museum specimens of song sparrows collected on the other side of the continent, along the California coast. Sure enough, as maximum temperatures increase, so did beak size… with one caveat. When the maximum temperature was higher than 98°F (37°C) beaks got smaller… just as was predicted by the original hypothesis. You see, if you took a song sparrow’s temperature the thermometer would read about 105°F (41°C). When the air temperature exceeds the bird’s own temperature, as it does in some regions, a larger beak could actually begin to absorb heat.
While the Smithsonian group has demonstrated a connection between climate and beak size, there’s still plenty of work to be done. For the new hypothesis to garner support, scientists need to see data that ties survival of wild birds to beak size-related heat dissipation.
Meanwhile, the fact that diet influences beak size and shape hasn’t changed—Darwin can continue to rest in peace. But as so often is the case, the more we discover the more we realize just how rich and complex this world and its inhabitants are … even an Earthling as seemingly plain and simple as a sparrow.
This 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!
© 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] Ame Otoko (toco toucan); Cephas (song sparrow); James Marvin Phelps (black-tailed jackrabbit); Mr. T in DC (house sparrow on drinking fountain); David Craig (song sparrow in hand).
How can one small voice cut through the cacophony of modern metropolitan life? A recently published study, combined with some earlier work, suggests that contrary to what you might assume, the secret to city communication isn’t shouting.
Urban background noise is heavily weighted toward the lower sound frequencies of 20 to 200 Hz—think diesel engines (50-60 Hz). That’s not to say there aren’t a lot of higher frequency noises in the concrete jungle but, compared to say, the rain forest’s tenor voice, cities sing baritone… and with enough projection to reach the last row of the balcony. Depending on the location and the time of day, your city may be belting out it’s theme song at anywhere from ~45-90 decibels (dB). Ever try to tweet over a lawn mower (and I don’t mean with your smart phone)?
People who haven’t yet experienced any hearing loss can detect activity in the 20 to 20,000Hz range. The faintest sounds we’re likely to hear register at about 0 dB. By 120 db we begin to experience discomfort or even pain. Now, as someone who loves to listen to nearly every kind of music, laughter in all its forms, Japanese prayer bells playing with a breeze, and rain bouncing on a tin roof, I’d be the first to agree that the human ear is a marvel. But compared to many of our fellow Earthlings, it’s… well, it’s pitiful. My wire fox terrier puts me to shame, easily picking up sounds from 40-60,000 Hz. The super-sensitive hearing of a bat, used for echolocation, ranges from 20-120,000 Hz.
According to the ever-useful Birder’s Handbook, we have more auditory commonality with birds, whose ability to discriminate between frequencies and degrees of loudness is on a par with our own. So perhaps we would be well served to take a page from the songbird songbook when trying to be heard in our rapidly urbanizing modern life. Researchers at the Universities of Copenhagen and Aberystwyth found that great tits (Parus major) living in urban habitats sing at a significantly higher frequency than their rural relatives. This finding coincides with previous studies reporting the same phenomenon for house finches (Carpodacus mexicanus), song sparrows (Melospiza melodia), white-crowned sparrows (Zonotrichia leucophrys), dark-eyed juncos (Junco hyemalis), and common blackbirds (Turdus merula).
Of course, going all Bee-Gees isn’t the only way a guy can get some attention from the talent scouts. A 2007 study from the University of Sheffield found that European robins (Erithacus rubecula) living downtown changed their performance times, from doo-wopping during the day to crooning almost exclusively after sundown when the din dies down a bit. In Berlin, nightingales (Luscinia megarhynchos) take the less subtle approach and just turn up the volume, at least on weekdays. But there’s a price to be paid for setting the amps to 11—a greater metabolic demand and more attention from predators. By broadcasting on a different frequency, some city songbirds have stumbled onto a low-risk solution to a major challenge of city life.
There’s incentive for avian adaptation (let’s not call it selling out) to make it onto the airwaves. You see, in the bird world the divas are all, um… divos. No, they don’t wear red plastic wedding cake hats and ill-fitting 1980s MTV fashion—that’s Devo. Let me put it another way: boy birds are the rock stars, girl birds are the groupies. Males warble (or learn to shred the guitar, or maybe groove a bass line) to get noticed by the ladies. If a gal likes a guy’s song she’ll hook up with him and probably become his baby-mama. But there’s a lot of competition out there and before you can score, you’ve gotta get heard.
Hey, singing falsetto to some chick may not be the most macho thing a fellow can do, but it beats spending Saturday night getting drunk at the karaoke bar with your buddies and going home alone.
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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: KaCey97007 (white-crowned sparrow); Dani_vr (seagull); Oystercatcher (common blackbird); Steve Harris (European robin); and TC Davis (song sparrow).
One of the things I like best about traveling is hearing different accents, turns of phrase, the variations in cadence and rhythms of speech unique to a specific place. Now that there’s a Starbucks on nearly every commercial district corner, and big box stores are shading out the retail undergrowth, it can be easy to forget you’re away from home until you exchange verbal pleasantries with a local.
Biologists have known for some time that dialects aren’t limited to the human population. Many wild bird species have them too. It can be harder for the untrained human ear to hear, but spectrograms of bird songs show distinct regional, local, and individual variation.
Recently, I learned that a member of my own extended family-of-choice has been traveling to Ecuador to study the dialects of rufous-collared sparrows (Zonotrichia capensis). In the process, Julie Danner—the new wife of my non-biological sister’s nephew—has discovered something about Andean sparrows, as they’re also known, that made even the New York Times take notice: Sparrow chicas are more likely to hook up with homeboys than with chicos who don’t sound like they’re from the ‘hood.
Or, in the language of a scientific journal such as The American Naturalist, where Julie, her husband Ray Danner, and their colleagues at Virginia Tech published their research results, female sparrows “gave significantly more copulation solicitation displays in response to their local dialect than to the song dialects from a population on the other side of an Andean pass (25 km away).”
The rufous-collared sparrow is the only tropical member of this genus and a close relative of the white-crowned sparrow (Zonotrichia leucophrys) found throughout most of North America. Initially, Julie studied two groups of birds but later expanded to eight populations. Her research suggests as little as 15 miles is enough to produce bird “accents.”
Recordings of male songs were made at varying distances from a home territory, along with the songs of other bird species. Then Julie put individual females into a holding cage and played the recordings.
“I found out that females distinguish between dialects and prefer the local dialect,” she explains.
Bird dialects seem to be formed by individual birds making slight errors in reproducing the characteristic tune of their species. These errors are picked up by new generations of young males, who don’t know any better, when they’re learning to sing love songs.
Scientists are pretty good describing what is happening in the world (e.g., female sparrows prefer local males) but it’s much harder to explain why. Is there any benefit to females and their offspring when they choose the boy next-door? Julie doesn’t know, but she’s come up with an educated guess.
“A male singing local song could be better adapted to the local environment. He may have better resistance to certain local parasites. A local male may just do better in that environment.” If that’s true, it could increase the likelihood that a female’s offspring will survive.
What’s true for birds is not necessarily true for those who study birds. Julie, who started her doctoral work in 2006 and hopes to finish up next year, is a Connecticut native. Her husband was born and raised over 1000 miles away, in my hometown of St. Louis, Missouri.