Science Daily reports a beautiful piece of research about shifts in White-crowned Sparrow songs as habitat has changed. Elizabeth Derryberry (now at LSU) compared recent recordings of male songs with songs from the same location from the 1970′s. At that time, the land had been cleared. Males’ songs (specifically, the trill portion) were generally faster and higher back then.
Derryberry argues that the males shifted to slower, lower-pitched songs which carry better through the dense foliage that now occupies the area. Confirming this idea, she was able to find one location where the foliage had not been allowed to return, and that population also had not slowed and lowered their songs.
Over the past few years, we’ve seen quite a few studies of environmental effects on bird songs. The effects are generally quite significant, helping us understand the extraordinary variability we face in learning bird songs and perhaps giving us just a bit of humility about the habitat changes we continue to impose across the planet.
A fascinating study out of the University of Guelph has documented changes over time in the songs of Savannah Sparrows. Studying 800 individual birds over the course of three decades, the researchers found that certain parts of the song did not change, but others were subject to strong pressures of cultural evolution. Some of these changes, particularly the shortening and lowering of the final trill, were strongly correlated with increased reproductive success, suggesting a cultural process of sexual selection.
For the most part, Savannah Sparrow males learn and sing only one primary song their entire lives. Young males learn their songs from their fathers, but also from their neighbors, and gravitate towards the more successful males. In this way, the dialects of the most desirable males tend to predominate. On Kent Island, at any rate, the sexiest song is one that ends with a low, short trill.
The full study can be downloaded here (PDF).
I’ve always thought that nest parasitism (e.g., cuckoos laying eggs in other species’ nests) seemed particularly evil and wondered what defences species have evolved against this. An amazing study from Australia has just come out showing that Superb Fairy-Wren mothers basically teach their chicks a food password. If the nestlings don’t give the password, they aren’t fed! Presumably, nest parasites (such as cuckoos) haven’t evolved the ability to learn the password and therefore won’t succeed.
The mothers actually vocalize these special calls to their eggs and the study shows that the babies learn the calls before hatching. Once hatched, the chicks’ begging calls include the “password call” that the mother gave. Different mothers give different calls and the study shows that these variations are not genetic but learned. It would be very interesting to know more about the call variations used by the mothers.
The other thing that would be amazing to observe would be a nest in which both alien and native babies were present—in order to see whether mothers actually feed their own babies and ignore the others.
Kenn Kaufman and Rick Wright have each done a good job parsing this year’s taxonomic revisions (PDF) from the American Ornithological Union. They agree that in some ways the biggest change this year is the shift in how we view the falcons, which are now seen as much more closely related to the songbirds than to the hawks, kites and eagles.
Intuitively, this is very surprising! One could certainly explain the similarities in form as the result of convergent evolution (ie., similarities in function and behavior have led to the evolution of similar physical “solutions”). In fact, completely unrelated species can share the same form, which is why anteaters and aardvarks both have long, sticky tongues (for eating ants).
What I find interesting about the hawks and falcons is that many of their vocalizations are so similar as well. For example, listen to these two cuts of a Prairie Falcon and a Northern Goshawk. If these species are only distantly related, then perhaps the similarity of sound quality and structure represents convergent evolution as well. That’s a fascinating thought, because it suggests that theses sounds are not arbitrary, but in fact highly adapted to the constraints of each species’ environment.
Researchers at Duke have shown an interesting new form of selective pressure on bird sounds: juvenile birds learning their songs prefer sounds that they can hear clearly. In some ways, it’s an obvious finding, but still has interesting implications.
Hand-reared Swamp Sparrows were exposed to a variety of recorded adult songs. Some of the recordings had been degraded by being re-recorded at a distance in typical habitat. Other recordings were not degraded. As adults, all of the sparrows sang clear songs; none learned songs that had been degraded.
Why is this interesting? In part, because many other studies have shown that birds are adapting their sounds to cope with human noise pollution. This is the first study that shows how it might be happening.
On a deeper level, this finding adds insight into how bird songs came to sound they way they do to begin with. They are adapted to habitat.
The full paper is in Biology Letters, but you’ll need a subscription.
Blake Mathys on the ABA blog had a nice piece recently where he posed the question: Why is sound so hard? In the piece, he laments, “I find identifying birds by sound to be extremely difficult.” Of course there are many, many birders who share his feeling.
So why IS sound so hard? Or at least, why do people think it is? I made some comments on the ABA blog, but wanted to expand on them here, mainly because I want to counter the suspicion many people have that it’s because they lack some native ability. In short, my answer is: Sound may be hard—but it’s not that hard.
Yes, there are some things that make sound inherently challenging, including:
1) Greater variability (esp., songs), compared to (many) plumages;
2) Transience (it’s much easier to compare something seen to a drawing or photo, than something heard to a recording);
3) Most people are visually dominant.
But these difficulties of sound are not the interesting part and not the main story. Every birder out there has already mastered a far more complex auditory skill: human language, and the same skills apply to bird sounds. (Scroll down to the bottom of the Larkwire Glossary to hear some examples of this.)
The problem is not that sound is inherently hard, it’s that the variability and the transience simply make clear that our approach to learning sounds is often flawed.
The fact is that cognitive psychologists could take you into the lab and train you up on nearly any skill, and do so very efficiently. They would do this by carefully controlling three things: 1) the timing of practice; 2) the structure of practice (roughly, from easy to hard); 3) the type of practice (basically, quizzing rather than sheer repetition).
Control these three factors and sound will not be hard.
So why is sound hard outside the lab? Because for most of us, the natural pattern of our exposure to bird sounds violates all three of these critical factors. Timing is too spaced out. Difficulty is random, not controlled. And when we do control timing and difficulty (using CDs), most of us just listen on repeat rather than test ourselves. The very gifted among us learn despite these hurdles; for the rest of us, it’s too hard!
Which is exactly why we designed Larkwire to control all three of these critical factors. The difference that highly structured practice—combined with explanations from a master ear birder—can make is nothing short of remarkable.
Of course, it doesn’t work overnight, but it can make what seemed to be an impossible task efficient and even fun.
Which one is it? (Credit: Macaulay Library)
Peter Kareiva, chief scientist for one of the world’s largest conservation organizations (The Nature Conservancy), has been on tour this year promoting “a new conservation ethic for the 21st century.” Simply because of TNC’s importance, this is a big deal for anyone who cares about the fate of nature on this planet. I was excited to read his essay (written with two colleagues) and also watch a talk he gave at the National Academy of Sciences.
There’s much to commend in his ideas, but also what seems to me a glaring flaw. If conservation is to have a “new ethic,” let’s get it right.
Kareiva starts from the unhappy fact that conservation is failing. We are losing the race to save biodiversity. Quite rightly, he points out that a strategy based primarily on “protected areas”—places where we exclude people to save nature—can’t succeed in a full world.
The new approach will concentrate more on “working landscapes”—farm fields, tree plantations, fisheries, urban ecosystems, and so on. At its core, conservation will become intertwined with sustainable development, helping people to live better lives by living harmoniously with nature rather than trying to save nature by excluding people.
(This, incidentally, is exactly what our first funding recipient—the Alliance for Tompotika Conservation— does, and it is why we fund them.)
This new conservation must work proactively to connect people (even in cities) to nature and ensure that nature is not seen as an enemy of jobs and prosperity.
So far, so good.
But Kareiva seems to want to go further, embracing the domestication of nature (PDF) by humans as natural, inevitable and a done deal. He says, stop romanticizing wilderness—there aren’t any truly untouched places anymore. Henceforth, our primary focus should be on the gardening of nature.
To me, this is a failure of both logic and imagination. It’s true that even in the most remote, “wild” places one can now find traces of human impact. But that hardly means there’s no difference between Denali National Park and Disney World.
We as a civilization and a species must collectively define our conservation ethic. If this ethic gives up on the idea of wilderness, for me and for many others, it will have failed completely. It will have given in to the idea that nature ultimately exists only for human exploitation. Many do hold this idea—and that’s their right. But those of us who disagree had better be clear about it and had better advocate for an alternative.
In Aldo Leopold’s Land Ethic, we are members of a community. As such, we are called on to share, not to take everything for ourselves. And I believe that includes leaving some places entirely alone.
I saw two Red-breasted Nuthatches at a local patch the other day and one of them appeared to be using pieces of dead wood as a tool. It would break off a piece of wood, hold it like a drill bit in its beak and hammer or probe with it. I saw it do this several times. Very exciting!
According to Birds of North America (subscription required), the only known tool use by this species is its use of pieces of bark as applicators for pine resin, which both male and female smear around the nest entrance (possibly to deter predators or competitors from entering).
The Brown-headed Nuthatch is known to use pieces of bark to probe and pry during foraging, and it’s been reported that Pygmy Nuthatches do something similar. So it wouldn’t be a total shock if Red-breasted Nuthatches can do this also. Pretty cool, nonetheless, if true.
What does all of this have to do with birdsong? Two things. First, language is the ultimate tool, so isn’t it interesting to think about how birdsong might prepare birds for other kinds of tool use? And second, I love all the mystery of this … to be reminded of how much we still don’t know about birds!