Posts Tagged ‘Evolution’

Singing Sparrows

June 6, 2014

Chipping_Sparrow

From The New York Times we learn that chipping sparrows love their neighbors, but only if they are weaklings. Male intruders can invade and take over another bird’s territory and strong invaders are usually the winners. Male chipping sparrows will form a neighborhood coalition to defend their territories, but apparently only if the intruder is weaker.  And how do they know this?  By the intruder’s song.  If the intruding sparrow’s trill is weaker, i.e. slower, then that bird is less aggressive.  A faster trill indicates a strong invader.

Stick to those music lessons, little chippers!

Click here to read the New York Times article.

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The Mockingbird Problem

July 7, 2010

We’re back from a birding/fly-fishing trip and will now finally address The Mockingbird Problem. Northern Mockingbirds – and about twenty percent of other passerine songbirds – are mimics. They steal their songs from their environments. Imagine the smartest student in class unnecessarily cheating on tests by going around the room and copying little bits of every other student’s answers.

That makes no sense. Instead of getting an “A” on the test, the student would get an “F” because her answers would be gibberish. Yet mockingbirds – obviously the star students in avian music class – do precisely that. Rather than develop their own unique songs, they just copy bits and pieces of the songs of other species.

Why?

Wouldn’t it be easier and less costly to invent their own songs and pass those down to their offspring? Less brain power would be required and learning would be simpler. Besides, the mockingbird isn’t fooling any other birds. They all recognize that the mockingbird isn’t one of them.

Nobody knows. We think we know that they sing for the same reasons as other birds: the males are seeking, stimulating, and keeping mates and they are competing with one another for mates and territories. But no one knows why they evolved singing songs of other birds. The same question can be asked about other mimics such as Common Starlings, Marsh Warblers, Australian Lyrebirds, bowerbirds, scrubbirds, and African Robin-chats.

Chihuahan Desert Mockingbird Locale (Otero Mesa)

We’ve learned a lot about Mockingbird song in the last century though. We know, for instance, that both males and females sing, although females sing only in the summer and only when their mate is off their territory. The males sing most in Spring, less in summer, still less in Autumn and hardly at all in winter. Unmated males sing more than mated males and will, in spring, sing all night long. (I’ve camped on the Chihuahuan Desert and listened to one sing all night long. That mockingbird may have been lonely, but he provided me with one of my favorite backpacking memories.) Unmated males sing in all directions, while mated males tend to sing inward toward their own territories.

Darwin's Mockingbirds

The males possess two entirely different repertoires, one for the spring and another for autumn. One had 203 songs in his mind. Somewhere between 90 and 150 seems about average. They continue to learn new songs for as long as they live. Older birds have larger repertoires than younger ones. Males with the most varied songs may get the largest territories. They may also mate earlier. And they sing all the time during breeding season, warbling away while copulating, eating, and foraging.

And probably they sing silently while dreaming. We know that Zebra Finches dream in song; no reason to suspect a bird that devotes as much of its cranial capacity to learning and remembering complex songs wouldn’t also dream in song.

They sing more during full moons.

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For more on Northern Mockingbird song see:

Derrickson, K. C. and R. Breitwisch. 1992. Northern Mockingbird (Mimus polyglottos), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/007

doi:10.2173/bna.7 (Subscription Required)

Frank Gill, Ornithology (3rd ed.), pp 230-231 and 237.

For a sample song, try this: http://www.birdjam.com/birdsong.php?id=4

The photo of the Northern Mockingbird at the top is by Manjithkaina, used via a Creative Commons license.

Why Do Birds Sing?

June 21, 2010

The short answer is, they sing to live. But that doesn’t tell us much. It is not a testable hypothesis and is at too high a level of generalization to be helpful.

And before we go any further, we pause to note that we are talking about bird song today, not bird calls. Calls are the comparatively simpler sounds made by birds to stay in contact with one another, to call for mobbing behavior, or to sound alarms. (Alarm calls, by the way, tend to be high-pitched calls which make the source of the sound harder for a predator to find.) Today we are talking about the more complex, difficult, and – to our ears, anyway – melodious songs of the passerines and other birds that sing.

Birds produce song by forcing air through the syrinx, a bony structure at the bottom of the trachea. The syrinx resonates sound waves generated by the vibrating membranes of the syrinx. Changing the force of the air controls volume while pitch is controlled by both the force of the air and the muscular tension applied to the membranes. Some birds can even produce two separate notes at the same instant because they can control both sides of the syrinx independently.

The two leading bird-song hypotheses of our time are that male birds sing to attract mates and to establish and protect territories. Those hypotheses are at least testable, have been tested, and look to be correct – as far as they go.

But even they don’t get at the root of the question. Bird song evolved along with birds. As far as we know, the dinosaurs from which birds evolved didn’t sing. (Maybe that’s the reason they died out! Nothing to do with volcanoes in Asia or a meteor strike in the Yucatán: They couldn’t sing! Of course, neither can I, so I am not fond of my new hypothesis about dinosaur extinction. If true, it doesn’t bode well for my continued survival nor that of my children, who can’t sing either.) The first dinosaur-birds probably didn’t sing and certainly did not have the highly developed language of many current bird species.

But at some point we must assume the male birds that croaked out rudimentary songs had a sexual advantage over their competitors who hadn’t figured out anything more than avian karaoke. Otherwise, they wouldn’t be singing today

Said differently, why weren’t the ordinary, simpler, and easier-to-learn bird calls enough?

For that matter, why did the males of so many species develop their brilliant colors? That too takes more evolutionary effort than dull and drab. Moreover, brilliantly colored birds are easier for those predators which have color vision to spot. The same is true for song. A robin singing away in pre-dawn light is easier for a predator to find than if the robin was emitting only an occasional high-pitched call. Why does the robin take the risk? Natural selection, after all, destroys without fear or favor. Why is a noisy robin more likely to pass along his genes than one sitting quietly hidden two feet away?

The possibility exists that beauty plays a role. Maybe the bird that sings most beautifully is the one most likely to breed in spite of the danger? For those of you with a scientific/materialistic frame of mind, nothing excludes such a possibility: Beauty may be adaptive. How else to explain the Elegant Trogan? For those readers of a more spiritual/religious framework, why would beauty not be a survival requirement? How else to explain the Elegant Trogan?

But before we can go further we have to deal with “The Mockingbird Problem.” We’ll be back next time to discuss mockingbirds and their songs.

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The photo of the fossil dromaeosaur  at the American Museum of Natural History in New York was taken by Dinoguy2.

Sandhill Cranes Return

November 12, 2008

As you can see from the photos, the Sandhill Cranes have returned and we are treated each morning to the sounds of the trumpets of evolution.

Sandhill Cranes

Sandhill Cranes

White-wing Doves Evolving

July 9, 2008

It is rare for a being which is deeply stupid to know it is deeply stupid and want to be smarter. But that dissatisfaction must be how life evolves from lower to higher states of consciousness. White-wing Doves are a case in point.

We’ve watched them try to figure out how to eat bird seed from a squirrel-proof bird feeder. This involves climbing all over the feeder, hanging upside down on it, pecking at it, much head-tilting and a lot of study. Soon, they are going to figure it out.

Last week a friend gave us one of those black pre-molded plastic ponds. We dutifully dug a huge hole for it, down through the rich topsoil in the garden and directly into the cement masquerading as dirt beneath. Following the easy instructions, we then went off to the local supplier of goods for ponds. Much is required: A pump, a fountain, water-lilies, nitrogen-fixing plants, one three-inch fish per each square yard of water surface (two in this case), food for the fish, food for the plants, and other essentials.

We purchased all this and took it home. The plants were fine and the pump worked well; too well, in fact. Our little pond contains about 250 gallons of water and the pump moves 300 gallons an hour which, according to the lady who sold it to us, was what we needed. The pump disagreed, shooting water upward and outward with far too much exuberance. It was moving at least 50 of those 300 gallons right out of the pond.

So we returned to the pond supply place to get something to diminish the pump’s enthusiasm. That turned out to be a diverting valve to which we attached tubing for another water outlet. The tubing is attached to fake turtles, fake rabbits or fake frogs which spout the water from their mouths.

Before investing in a fake turtle, we thought it best to go home to see if the diverter idea worked. It did. The spray was much lower and all the water stayed in the pond. That meant yet another trip to the store for the fake turtle. (The books which assure you that these projects only take, for example, four hours don’t count the fifteen trips to the store to get one more part you didn’t know you needed. Or another water-lily.)

Finally the pond was working. We buried the power cord and drilled holes in the fake wood stump where the fake turtle now sits, gushing water into the pond with a delightful sound.

Then we fed the fish. That interested the Border Collies which are already evolved. They like the fish food and we’re not so optimistic about the long-term survival of the fish either.

Border Collies also like fresh cool dirt. The pile of dirt removed for the pond apparently was not in the right place so, while we were inside, they rearranged the dirt pile, shoveling a lot of it directly into the pond.

They didn’t like the words we used when we discovered that, so they let us bail it out and clean it up by ourselves.

But now the pond is working just fine and everybody is happy. It is attracting all manner of wildlife, including birds and frogs (Or are they toads? I must learn the difference; I’m trying to evolve too.) The Hummingbirds fly into the fountain’s spray and the turtle makes a nice perch if you are a House Finch.

The Mourning Doves enjoy the pond too. Unlike their cousins, the White-wing Doves, they walk right up to the edge and have a drink. But as I said before, the White-wings aren’t very smart and I watched one for ten minutes this morning. It walked nonchalantly around the pond, glancing at it often. Then it climbed up on one of the pieces of sandstone on the edge of the pond, casually lifting and stretching one wing and then the other. Then it backed down and studied the situation for a while. A Mourning Dove walked by and had a drink. The White-wing hopped up on the bucket we used to bail out the pond and studied some more. Then it hopped down and went right up to the edge of the pond but a drop of water must have hit it because it startled and flew off. Half an hour later, it was back; still studying. As far as I know, it still hasn’t had a drink, but I’m confident it will evolve a bit further and solve this problem too.

Passeriformia Dreaming

July 2, 2008

When you go to sleep tonight maybe you’ll be like Hemingway’s old man and dream about the lions. Or the snakes. Or being late for a plane. Or flying without an airplane. Or flunking a test. Or any of a multitude of other dreams. But you will dream.

Nobody knows for sure why. We spend about two hours a night dreaming. Freud thought it had to do with subconscious desires. More likely, dreaming is a part of the process of transferring and synthesizing stimuli. It may be an integral part of learning. That may be when we transfer information from the hippocampi to the neocortex for long-term memory.

We’re not the only dreamers. All mammals dream and in ways similar to humans. That’s not a surprise; mammals’ brains are built pretty much the same, with a cortex governing complex processes and behavior. Mammals sleep in stages; successive episodes of slow wave sleep (SWS), intermediate sleep (IS) and rapid-eye movement (REM) sleep. As the night progresses there is relatively less SWS and more REM.

Dreaming occurs during REM sleep when the brain’s cortex is active. That’s why we thought that a cortex was required for dreaming. Birds and reptiles don’t have one and no one has ever caught a reptile or a bird dreaming.

Until recently.

Birds were known to have periods of non-rapid eye movement sleep (NREM) but only very short bursts of REM sleep. Nor were birds known to have a sleep-stage structure similar to mammals.

But now comes news that Zebra Finches, and presumably other passeriformes (songbirds) sleep in stages much like ours and spend time dreaming. Conclusion? Dreaming does not require a cortex.

And that raises all kinds of questions. For instance, if a cortex is not required for structured sleep, why has evolution designed two entirely separate mechanisms for doing just that? If it has, dreaming must be really important. Perhaps we can learn more about our own dreaming from birds’ dreams.

Are bird brains a great deal more complex and capable than we once thought? (The answer to that is almost surely, yes. We’ve already observed similarities in our brains and avian brains at the molecular and cellular level. A cortex may not be such a big deal after all.)

neuronal structure of cortex

Why have we now seen this type of sleep structure in song birds but not other birds? (Perhaps because songbirds must learn more complicated songs and behaviors? Or maybe we’ve just missed it in other birds? Some parrots and hummingbirds learn vocalizations and they don’t seem to dream.)

Finally, what do birds dream about? And how would we ever know? We can’t even really describe our own dreams. As Marlow says, describing the beginning of his journey into Conrad’s Heart of Darkness,

“It seems to me I am trying to tell you a dream — making a vain attempt, because no relation of a dream can convey the dream-sensation, that commingling of absurdity, surprise, and bewilderment. . . , that notion of being captured by the incredible which is of the very essence of dreams. . . .No, it is impossible; it is impossible to convey the life-sensation of any given epoch of one’s existence — that which makes its truth, its meaning, its subtle and penetrating essence. It is impossible. We live, as we dream — alone….”

But not as alone as we once thought.

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The entire scientific paper upon which this entry is based can be read here. From the paper comes this two dimensional view of a computer model of the finches dreaming. Every dot corresponds to three seconds of a bird’s sleep, SWS in blue, IS in cyan and REM in red. (Image courtesy of Dr. Phillip Low, the article’s lead author.)

Bird Dreaming


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