IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow. We're broadcasting from Cornell University in Ithaca, New York. It's in central New York, south of Lake Ontario. And every year around this time, huge throngs of migratory birds pass here on their way south for the winter.

Now, you might be picturing geese gliding south in the V-formation, you know, the sort of Central Casting picture for migrating birds. But all kinds of other birds do it, too, and ones you might not see because they migrate at night. And some of them are so tiny, they only weigh about as much as a Hershey's Kiss, and even those tiny birds can wing their way from the Great Lakes to warmer wintering grounds down south.

So how do these little birds, tiny little birds fly so far? How do they know where they're going at night without a GPS, a map, all the navigational tools we humans need?

Well, this hour we're joined by four migration experts. We'll talk about what they've learned tracking the birds, the mysteries of migration they still haven't solved. We'll be answering your questions, too. Our number is 1-800-989-8255. We're also Twittering. You can tweet us @scifri. That's @-S-C-I-F-R-I. And if you're here in the audience at Cornell's Bailey Hall, I invite you to step up to the microphones and ask a question.

Let me introduce my guests. David Bonter is leader of Project FeederWatch at Cornell Lab of Ornithology here in Ithaca. He's also vice president of the Braddock Bay Bird Observatory on Lake Ontario. Welcome to SCIENCE FRIDAY, Dr. Bonter.

Dr. DAVID BONTER (Ornithologist, Cornell Lab of Ornithology; Vice President, Braddock Bay Bird Observatory): Thank you for having me, Ira, and thanks for bringing SCIENCE FRIDAY to Cornell University.

FLATOW: Our pleasure. Andrew Farnsworth is a post-doctoral researcher at the Cornell Lab of Ornithology. Thank you for being with us, Dr. Farnsworth.

Dr. ANDREW FARNSWORTH (Post-Doctoral Researcher, Cornell Lab of Ornithology): Thanks for having me, Ira.

FLATOW: You're welcome.

FLATOW: Mark Deutschlander is an associate professor and chair of the biology department at Hobart and William Smith Colleges in Geneva in New York. It's right by, right close to here. He's also president of the Braddock Bay Bird Observatory. Welcome to SCIENCE FRIDAY, Dr. Deutschlander.

Dr. MARK DEUTSCHLANDER (President, Braddock Bay Bird Observatory; Professor of Biology, Hobart and William Smith Colleges): Thank you so much, Ira.

FLATOW: On the phone is Sidney Gauthreaux. He is professor emeritus in the department of biological sciences at Clemson University in South Carolina. Welcome to the show, Dr. Gauthreaux.

Dr. SIDNEY GAUTHREAUX (Professor Emeritus, Department of Biological Sciences, Clemson University): I'm glad I could join, Ira.

FLATOW: Thanks for being with us. David, let's ask - let me ask you first. We always think of birds migrating during the day. Why aren't these birds doing it at night? Do they actually migrate better at night? What's the point here?

Dr. BONTER: That's a great question, and the vast majority, actually, of the small songbirds do migrate at night, and they take off about a half an hour or an hour after sunset. And they're - it's uncertain as to exactly why they do migrate at night, but it probably has something to do with the fact that the atmosphere is a lot calmer at night. It's easier to avoid predators that might be able to catch them during the daytime, and just the cooler temperatures would keep them from overheating while migrating at night, as well.

FLATOW: Mm-hmm. Andrew, we actually have a recording you made of some of the birds migrating at night. Let's see if we can listen to that now.

(Soundbite of static, birds chirping)

FLATOW: Now, Dr. Farnsworth, to the untrained ear, that just sounds like a bunch of birds…

(Soundbite of laughter)

FLATOW: …in the pet shop, you know what I mean?

(Soundbite of laughter)

Dr. FARNSWORTH: It is a bunch of birds.

FLATOW: What's so special? Do you hear something? I'm sure you hear something I don't hear when you listen to those birds.

Dr. FARNSWORTH: So what I'm hearing are primarily Swainson's thrushes. It's a small relative of American robin many of you may be familiar with. And all those recordings were made at night. It's a unique call that these thrushes are giving that is almost used exclusively during nocturnal migration to keep the birds together, perhaps to cue them when to come down. So it's a pretty unique vocal behavior and something that happens primarily at night, tells you what species are up there. Pretty cool.

FLATOW: How do you record them? Can you just go under the birds and stick a microphone? Can we all do that?

Dr. FARNSWORTH: You can use any kind of microphone. You could probably use the microphone we're speaking into. It'd probably be a little bit better to have one that were designed for the elements. You put this thing outside, and it might not do too well in the rain. But yeah, basically you can stick a microphone outside. Anybody can do it. You could build one. You can buy one. Very simple.

FLATOW: Can you actually predict - I'll ask all of you - can you predict the migratory paths or where these same birds are going to be flying every year? David? Are they pretty narrow?

Dr. BONTER: For songbirds, it's basically a broad-front migration. So they move between their breeding grounds, and a lot of the songbirds that are passing through here now are breeding in the northern forests, and they're passing on down to spend the winter in Central or South America or even in the Southeastern United States or the Caribbean. And the path that they take really depends quite a bit on the winds.

FLATOW: Is that right?

Dr. BONTER: These are small birds, and you can imagine that they're blowing around quite a bit. So an individual bird won't follow the exact same route one year to the next, and they do pay very close attention to the winds aloft and only migrate when they have the proper tailwinds to help them along the way.

FLATOW: And they know this collectively, when the right - no one's directing traffic? It's take off now?

Dr. BONTER: Yeah, well, and the amazing thing is that this time of year, a lot of these birds that are flying are really only a few weeks old. They were born in June or July. The vast majority of the birds passing over now are young birds. So they may have only been independent from their parents for a few weeks, and they're undertaking these incredible migrations on their own.

FLATOW: Wow, at such a young age. And how many migrations will they do in their lifetime?

Dr. BONTER: Small songbirds like the birds that are smaller than robins can live to be about 10 or 12 years old. Now, the vast majority of them actually don't make it past year one. So migration is a very strong, selective factor. But, you know, on the average, probably these birds live to be two or three years.

FLATOW: And what kinds of birds are we talking about? Can you name some of them?

Dr. BONTER: We're talking about all the warblers and vireos and the thrushes, birds like nuthatches, all the small songbirds.

FLATOW: Yeah. I saw the nuthatches were gone from my feeder for a while.

Dr. BONTER: Oh, they'll be back.

FLATOW: They'll be back. That's good. Mark, how do the birds know where they're going? How do they keep track of where they are?

Dr. DEUTSCHLANDER: Well, you mentioned a map, a GPS and a compass at the beginning of the show, and they actually have a couple on-board compasses. They can use cues at sunset like the setting sun itself, where there is polarized light in the sky that they can see that we can't see that actually points north.

They also can use the stars. They learn at a very young age which star is at the center of rotation, and they have a magnetic compass. So they have multiple compasses to help them find their way.

FLATOW: This is fascinating about using the stars. They're actually looking up and navigating by the North Star?

Dr. DEUTSCHLANDER: Yeah, they actually learn which one isn't moving, and there was a series of experiments that were done by Steve Emlin(ph), who is a Cornell professor, and this is in the '70s. And he put indigo buntings, which are a type of songbird, into a planetarium, and he could rotate the stars however he wanted to in the planetarium, and he convinced a bunch of the buntings that Betelgeuse was the pole star because that's what - the one that wasn't moving in his experiments.

FLATOW: He put them in a planetarium.

(Soundbite of laughter)

FLATOW: And he made, instead of the North Star, he made Betelgeuse the North Star.

Dr. DEUTSCHLANDER: That's correct.

FLATOW: And they flew thinking - they obviously lived there and thought that - and they - that's amazing. Wow.

Dr. DEUTSCHLANDER: And they weren't flying around freely in the planetarium.

FLATOW: Right.

Dr. DEUTSCHLANDER: He designed a funnel that we still use today called the M-1 funnel. And the veterinarians in the second half of the show will probably know what I'm talking about, but it's like an Elizabethan collar, which you put around a dog or a cat when they have stitches.

FLATOW: Right.

Dr. DEUTSCHLANDER: So it's small at the bottom, large at the top, and you place a bird in the funnel. It's not wearing it around its neck, but it goes inside the funnel with a top on it. And the birds will hop in these funnels in the direction that they would be migrating. And you can use typewriter correction paper or thermal paper or an ink pad in the bottom with blank newspaper and see where they're going.

FLATOW: So you see their little - the prints they leave on the paper, the direction. And they thought - when they were brought up to think that that was the North Star, they used that for navigation.

Dr. DEUTSCHLANDER: Yeah, they did.

FLATOW: Wow. And so when they're flying, are they constantly looking at the North Star?

Dr. DEUTSCHLANDER: I don't know if they're looking at it constantly, but they're definitely looking at it on occasion to see where it is.

FLATOW: So, I'll bring - Sid Gauthreaux. Sid, you pioneered using radar to track the migration. Do you actually - can you actually see a burst of when the birds are migrating?

Dr. GAUTHREAUX: Actually, you pick up birds and insects. Anything that has moisture in the atmosphere will give a reflectivity to radar. And, of course, birds are moving in the atmosphere at much faster speeds than insects. So with these new Doppler radars that give us velocity information, we're able to discriminate migrating birds from just nights with lots of insects in the atmosphere.

FLATOW: Mm-hmm. And so when nighttime happens, if you had your radar screen going, you would just see just a burst of activity as the sun's going down?

Dr. GAUTHREAUX: It's tremendously impressive, looking at a radar screen. Near sunset, there's very little activity, maybe a few insects in the atmosphere, but 30 to 45 minutes after sunset, it looks like an explosion. And Doppler radars are colorful so that all these colors appear on the screen, and, of course, the velocities increased dramatically as birds take off and fly up into the radar beam and are tracked by the radar beam.

And we have a network of 150 of these radars across the United States. So it's rather difficult for migrating birds to avoid detection, if you know what I mean.

FLATOW: So we can actually go on the Internet and watch these birds migrating?

Dr. GAUTHREAUX: Absolutely, absolutely. There are several different providers of Internet radar images. You know, weather underground is one. RAP-UCAR is another source. And anyone can look at these displays, and then some of them, you can go back. There's an archive so that if you happen to be looking at it and wanted to see what it looked like before sunset, you could just change the time, and it'll show you the image before sunset.

FLATOW: How do you know you're not mixing up the birds with the big water droplets or a storm coming?

Dr. GAUTHREAUX: Well, rain has a very different display on weather radar. Of course, raindrops are very strong reflectors. And the shape of rainstorms, you know, a general rain covers a tremendous amount of geography, or you can have isolated thunderstorms with very strong reflectivity. But the pattern, the morphology of rain is very, very different than the morphology of what you see in terms of birds.

Remember, most birds at night are probably flying somewhere between 1,200 and 1,500 feet above the ground, some above that, and there are certainly some below that. But if you had to choose an altitude where most birds are flying over the ground at night, it would be somewhere in the vicinity of 1,200 to 1,500 feet above the ground.

The radar beams are generally tilted - that you get information from the Internet - tilted about a half-a-degree up. So you go through a layer of birds and insects, and eventually you go above the bird layer, and that's what defines the edge of the radar return.

So if you look at a display at night, when there's bird migration, oftentimes what you see is a disc with the radar station in the center of the disk and varying colors reflecting different levels of reflectivity - more close to the station at lower altitudes and, of course, none after you get above the insect and bird layer.

FLATOW: All right, Dr. Gauthreaux, I'm going to have to take a break here. And we'll also take a break and come back and talk more with David Bonter, Andrew Farnsworth, Mark Deutschlander and Sidney Gauthreaux.

Our number: 1-800-989-8255. Also, you can tweet us, @scifri. Stay with us. We'll be right back after this short break.

(Soundbite of music)

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

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FLATOW: You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. We're here at Cornell University's Bailey Hall in Ithaca, New York. And I want to give a shout out to some of the high schools that have come to join us today.

Represented here: Binghamton High School.

(Soundbite of applause)

FLATOW: Yeah, sure. Groton High School, Spencer-Van Etten High School. We also have some students, sure, from the New Visions Health Sciences Program at Cuyuga Medical Center and Thompkins Cortland Community College. Welcome to all of you for coming by SCIENCE FRIDAY.

(Soundbite of applause)

FLATOW: We're talking this hour about bird migration: How do they know where to go? How do we track them? My guests are David Bonter of Cornell Lab of Ornithology, also from that lab is Andrew Farnsworth, Mark Deutschlander from Hobart and William Smith Colleges in Geneva and Sidney Gauthreaux from Clemson University in South Carolina.

FLATOW: We had a little clip of audio before. I want to play another clip, of what goes on inside that bird-banding station at Braddock Bay on Lake Ontario, because I want to talk about bird-banding and how that works. It sounds like a little wacky stuff going on in there. So let's play that clip now.

Unidentified Woman #1: The wing on my white throat is…

Unidentified Man #1: Male 1-1. Did I tell you that?

Unidentified Woman #1: Seven-one.

Unidentified Woman #2: One-eight point six. Excuse me, mass and (unintelligible)…

Unidentified Man #2: Which also makes it unknown sex. Is that right?

Unidentified Woman #2: Yes.

Unidentified Man #2: Because I don't really see a buffy(ph) edge on it, so…

(Soundbite of birds chirping)

FLATOW: What's going on in there, David?

(Soundbite of laughter)

Dr. BONTER: Well…

FLATOW: This is bird-banding, right? Not that…

Dr. BONTER: It is bird-banding, yeah, yeah. And up at Braddock Bay Bird Observatory and at a few other locations across North America each spring and fall, we actually put nets up out in the habitat and catch birds while they're actively migrating south and stopping at our site along the way. And we bring them into the banding station there. We put a numbered tag on their leg, and every bird will receive a unique-numbered band on their leg. We take a whole bunch of measurements, so you heard folks there calling out measurements and aging the birds and sexing them and looking at their energetic condition, and that's really what it's all about.

FLATOW: Now, how important is that little band? You know, do you wait for the birds to land someplace, and somebody will phone you in, send you a postcard: We found a bird with 5738 on their leg or something?

Dr. BONTER: Yeah, that certainly happens. And all of the birds banded in the U.S., Canada and Mexico receive unique identifying numbers on their legs. So as we put a band on the bird, if that's recovered elsewhere, we know exactly where that bird was banded and can connect those dots.

But the real reason why we band the birds at Braddock Bay is to take a look at the energetic condition of the birds while they're migrating, take a look at how long they're stopping at the site. We can take blood samples, extract DNA and learn a whole lot more about the biology and the ecology of these birds while they're migrating.

FLATOW: So the band is just an extra, added attraction.

Dr. BONTER: Yeah, the recoveries of birds elsewhere, it's really great, but what - we're going for additional information, as well. And we have had a few really interesting recoveries.

A few years ago, we banded a bird called a gray catbird at Braddock Bay, and two weeks later, it was recovered on an oil rig in the Gulf of Mexico. So it had gone from Lake Ontario to the Gulf of Mexico in two weeks.

FLATOW: Did it stop along the way?

Dr. BONTER: It probably did. Yeah, it certainly did.

FLATOW: Refueled a little bit. Mark, did you want to say something?

Dr. DEUTSCHLANDER: The recoveries, even though they're small, they are important to help us learn about orientation mechanisms, as well. So, you know, thousands of these birds are being banded a year, hundreds of thousands. And so small recoveries are still important, but like David said, for the majority of the birds, we're not getting that data.

FLATOW: Let's go to the audience. Right here, let's start on this side. Yes.

Unidentified Woman #3 (Audience Member): How many species of birds migrate?

FLATOW: How many species of birds migrate?

Dr. DEUTSCHLANDER: Wow, that's a great question.

(Soundbite of laughter)

Unidentified Man #3: So in the world, across the whole world, there are about 9,600, 9,700 species of birds. Here in North America, we probably have about 250 that are migrating through. I'd say somewhere in that neighborhood.

Dr. DEUTSCHLANDER: Maybe even a little more than that, you know, 300, 400. It depends. In some - there are a number of different ways you can actually classify migrants, but the kind that we've been talking about, these nocturnal migrants, he's probably right, probably, you know, in the 300 range, something like that - in the U.S.

FLATOW: Did you want to add something?

Dr. DEUTSCHLANDER: Not all birds do undertake these long-distance migrations, going from, say, Alaska down to South America. There are a lot of different kinds of migrations. So some just move a few hundred miles, whereas some do undertake these really remarkable migrations of thousands of miles.

FLATOW: Mm-hmm. Question from a tweet came in from Alan Ekhert(ph), who says: Does light pollution affect the bird's compass? When they - if they are looking at the North Pole…

Dr. DEUTSCHLANDER: Good question.

FLATOW: Are they going to get confused by all these other lights around?

Dr. DEUTSCHLANDER: They can get confused, especially on those nights where there's a lot of cloud cover, a lot of mist in the atmosphere. They're a lot like we are. You're lost and you see light, you're liable to go towards that light to find where you are. And so they will go to lights on towers, on cell-phone towers, on wind-turbine towers, even that of buildings.

So it can be a problem. I don't think it's really a big problem for them on, you know, well-lit nights when it's very clear because then, as Sid said, they're pretty high up in the atmosphere.

FLATOW: Well, let me ask, Sid. Sid, is light pollution a problem?

Dr. GAUTHREAUX: Actually, light pollution is a fair problem, and we've actually had now two studies that demonstrate that the worst lights on tall communication towers are the ones that are red, constant glow and alternating with slow off-on. Those towers and those red lights with constant-burning lights attract far more migrant birds at night than do the white-strobe or red-strobe towers. And in light of these two studies, the FAA is actually reexamining lighting on tall communication towers.

Of course, it has to be there for air safety, but they are really welcoming the new data and are thinking seriously about changing the requirements. So that's going to be really great for the conservation of migratory birds because these tall towers - remember, they don't actually crash into the tower in many instances. They crash into the guidelines that are un-illuminated as they're flying towards these lights or circling the towers repeatedly.

Birds also are attracted to offshore platforms, oil and gas platforms. And a recent study in the North Sea has demonstrated that if the platform is illuminated with green wavelengths and the workmen can still accomplish their work, it's far less attractive to migrating birds. So we're making some progress in that arena.

FLATOW: Yeah, I heard about that bird that landed in the Gulf of Mexico on that platform. Let's go to the audience here. Yes.

Unidentified Woman #4 (Audience Member): Yeah, well, speaking of air safety, there was a mention of using Doppler and birds. Is there some coordination that could be done, or is there work being done to help out the aviation industry?

FLATOW: You mean from crashes into planes?

Unidentified Woman #4: Correct, exactly.

Dr. GAUTHREAUX: Actually, that's a very active area right now. The FAA is funding evaluation of small, mobile radars that can detect migrating birds, and these radars really just detect birds maybe within something like six miles or so, particularly the large, dangerous birds, and they're thinking about deploying these radars at various airports. That's one solution.

The Doppler network is also being considered another solution, because it detects migration movements and measures the density of those movements so that in - when the first real freezes come, and waterfowl are leaving Canada and coming south, sometimes those concentrations are so great that air traffic control radar is blanketed by these migrating birds.

Under those circumstances, warnings can go out and notify aviation interests that there are dangerous concentrations of birds in the altitudes where they're flying.

FLATOW: 1-800-989-8255. Carol(ph) in St. Paul. Hi. welcome to SCIENCE FRIDAY.

CAROL (Caller): Yeah, hello. Hey, I was wondering: How many migratory birds, on an annual basis, just don't make it. You know, in terms of survival of the fittest, how many just don't do it? And then are there some birds that are better migratory survivors than others?

FLATOW: Good question. David?

Dr. BONTER: It's a great question. In general, these small songbirds have about a 50-50 chance of surviving from year to year. So if you have a pair of sparrows that reproduce, and say they have five or six young, one of those young has to make it back the next year in order to replace the parent that will not have made it.

So if you're looking at a nest of five or six young, chances are only one of those will successfully migrate south, live through the winter and make it back in order to nest.

CAROL: All right.

FLATOW: All right, thanks for calling, Carol.

CAROL: Thanks.

FLATOW: 1-800-989-8255 is our number. Let's go over here, this side of the room. Yes.

Unidentified Woman #5 (Audience Member): Hi. Recently, a weatherman on one of the local public radio stations stated, actually, on two separate occasions over the last couple of months that global warming was not real. He cited, on the first occasion, that we are actually in a cooling trend right now due to low sunspot activity. And on the second occasion, he said that the flooding in some part of the world recently, after years of drought, was evidence that nature always corrects itself. He seems to be ignoring a lot of other evidence, like the melting of…

FLATOW: Do you have a question in this?

Unidentified Woman #5: Yeah, I do. Like the melting of the polar ice caps. Can you speak about how changes in bird migration speaks to the subject of global warming?

FLATOW: Andrew?

Dr. FARNSWORTH: So - as you might imagine, just the fact that there are many species of birds that migrate lends itself to thinking about migration as a response to changes in climate at a very sort of local level in time, so seasonally, but also over thousands and hundreds of thousands and perhaps even longer periods of time. So when we think about changing climate and perhaps rapidly changing climate, there are going to be responses that we see from migrants. Because a lot of species are adapted to these movements, to escaping, you know, sort of seasonally poor conditions or things like that, you're going to see situations where - when climate changes rapidly or where you see swings to cold or warm temperatures or stormy or non-stormy times, wet or dry times. Birds are definitely going to respond to that.

FLATOW: Have we seen this already? Patterns changing?

Dr. FARNSWORTH: I think we have. I think…

Dr. GAUTHREAUX: I think there's ample evidence that's been published that short-distance migrants - we call those temperate migrants because they don't go all the way to the tropics in winter. Short-distance migrants, temperate migrants, are responding much more rapidly than long-distance migrants. That -and that's a source of some concern because birds want to reproduce when their food supply reaches a peak so they can provision their young. And there is some concern, in the case of long distance migrants, that global climate change is advancing migration schedules and so forth in short-distance migrants.

But the long-distance migrants don't seem to be responding accordingly, which could lead to a disconnect, if you will, between peak resource and when the migrants actually arrive there. So there's concern for long-distance migrants, and a lot of research is looking into that. But there's clear evidence that the short-distance migrants are, in fact, responding. Birds are arriving on their northern breeding grounds earlier, in some cases a week or so earlier than they have historically.

FLATOW: And you're shaking your heads in agreement. Yeah.

Dr. FARNSWORTH: Yeah. We agree with Sidney.

(Soundbite of laughter)

FLATOW: It's hard to disagree, I get that. I'm getting that impression. Let's go to the - in the audience here. Yes, sir.

Unidentified Man #4: Yes. I live in Scottsdale, Arizona. And there's been an article recently that the common sparrow's population has been decreasing about 2 percent a year from the last several years. Would that be possible because they're migrating somewhere else because it's too hot in Phoenix?

FLATOW: You mean they're not showing up in Phoenix, is what you're saying.

Unidentified Man #4: Well, they're - yeah. They're - yeah. They're…

FLATOW: They're going somewhere else.

Unidentified Male #4: The retirees are going there, but the sparrows have decided that they'll leave at 2 percent a year.

FLATOW: So snowbird means something else now.

Unidentified Man #4: It does, right.

FLATOW: Going to some other place.

Unidentified Man #4: Yeah.

FLATOW: Could that be? What do you think? Could it be - could it get too hot for them to go and they would go some place else, David?

Dr. BONTER: Well, bird populations are changing all the time. And it's really hard to know what's going on with the population in one area and what causes fluctuations there. But we certainly know that some groups of birds are on the decline. The birds that nest in grassland habitats tend to be doing very poorly right now in North America, whereas here in Northeast, a lot of those forest-breeding birds are actually doing better now than they have in many decades because we have the regeneration of forests as agricultural lands are being abandoned.

So there are definitely winners and there are losers out there, and it's really important to look at this at a large scale rather than what's going on in an individual community. We need to monitor birds over large spatial areas to know how populations how doing in general.

FLATOW: You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow here in - talking about birds here in Ithaca, New York, at Bailey Hall with our guests. Our number: 1-800-989-8255. Here's a question that came in from Second Life: How far can a typical hummingbird fly between meals? I saw hummingbird on an oil rig 120 miles from shore in the Gulf of Mexico. Do you follow hummingbirds, also? Well - yeah.

Dr. BONTER: Yeah. They do fly across the Gulf of Mexico so - and they can't stop unless there's an oil rig out there. So I would say that's probably the longest distance that a hummingbird is going to fly.

Dr. DEUTSCHLANDER: I love flowers in the Gulf of Mexico. Yeah.

FLATOW: And - well…

(Soundbite of laughter)

FLATOW: Do they rest in - altogether when they rest for some - they - do they not fly at all during the day, so every day they're on the ground and at night they're flying?

Dr. BONTER: Well, hummingbirds are actually - for those - from the eastern U.S. and the ruby-throated hummingbird, the common hummingbird here, they are diurnal migrants. So they're feeding as they're migrating. What Mark is talking about where birds are actually crossing the Gulf of Mexico, because it's a diurnal situation, obviously, and there's no food, they're going to stop whenever they can, which are oil rigs. But, otherwise, in a lot of cases, even though you may see hummingbirds migrating during the day, passing a hawk lodge or even passing, you know, your school or anything like that, that you may see them stop at a brilliant flower along the way at some point to feed. They may be able to move tens or hundreds of miles in a day, but they may also stop along the way when they can.

FLATOW: Mm-hmm.

Dr. GAUTHREAUX: Hummingbirds almost double their weight. David was talking about fuel for flight. And humming - there are records of hummingbirds that were weighed when they were lean and then weighed right before they departed. And they almost doubled their weight in some cases. It's expensive to carry that extra fuel, but a hummingbird flying north across the Gulf of Mexico meeting a cold front with adverse winds could use that fuel supply rather quickly. And oftentimes, these are the birds that stop on the oil rigs. They're energetically compromised, so to speak.

FLATOW: Mm-hmm. So is it true that you track some of these migrating birds by looking at the moon?

Dr. GAUTHREAUX: Yes. In fact, that was - my major professor, George Lowery at MSU actually championed that particular technique. And by taking a telescope, at least a 20-power telescope and directing to the nearly full moon on a cloudless night, you can actually, on a night of reasonably good migration, see the silhouettes of birds passing before the disc of the moon. We actually have used that technique, which is quantitative to calibrate and quantify our radar displays.

FLATOW: It's that reliable?

Dr. GAUTHREAUX: It is.

FLATOW: And you'll see - and just by counting the birds, you know, how many birds fly past the moon, you can get a good idea of the…

Dr. GAUTHREAUX: That's correct. And, of course, the higher the moon is, the greater the correction factor, because the volume - your cone of observation is much narrow when the moon is overhead than when it's a 20, 30 degrees above the horizon. So all the math has been worked out, and it's a rather incredible technique and very, very easy to do.

FLATOW: All right. Well, we're going to talk more about migrating birds here at the Bailey Hall. Our number is 1-800-989-8255. We're talking with Dave Bonter, Andrew Farnsworth, Mark Deutschlander and Sid Gauthreaux, and also taking your calls and your tweets. You can send us a tweet @scifri, at @-S-C-I-F-R-I, and step up to the mic and in the audience here. We'll take lots of more calls when we get back. Stay with us. We will be right back after this break.

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FLATOW: I'm Ira Flatow. This is Science Friday from NPR News.

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FLATOW: You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. We're talking this hour about the bird migration: how it evolved and why birds do it, what's going on - there all kinds of questions about it - with my guests, David Bonter and Andrew Farnsworth of the Cornell Lab of Ornithology, Mark Deutschlander of the Hobart and William Smith Colleges in Geneva, and Sidney Gauthreaux of Clemson University in South Carolina. Our number: 1-800-989-8255. Let's go to the audience here in Bailey Hall in Ithaca. Yes?

Ms. STEPHANIE JANE(ph) (Audience Member): Hi. My name is Stephanie Jane, and I'm from Atlanta, Georgia, and I just wanted to know: How does banding affect the birds, if at all?

FLATOW: Yeah. They got to carry this very heavy piece of metal with them, right?

Dr. BONTER: Actually, it's not very heavy. It's - the bands are made out of aluminum, and they rotate and can move up and down the leg of the birds so it doesn't constrict their movement in any way. And, actually, if you put a band on a scale, it will barely even register. So, the birds often fly away and don't even notice that it's there.

FLATOW: Flora Lichtman, our video producer, will be around a little later to talk about - that's our Video Pick of the Week this week, actually going to the lab and watching them do the bird banding. So you'll be able - Flora will come out and then talk about that a little bit later.

Let's go to this side of the hall. Yes, sir?

Mr. MIKE BLACK(ph) (Audience Member): Mike Black, Dundee, New York. The question is about the brown bat colonies that are being decimated by parasites, I believe. Is that from migratory movement? Is it being spread that way?

FLATOW: Do you follow the bats, or just the birds?

(Soundbite of laughter)

FLATOW: We won't talk about the bees.

Dr. FARNSWORTH: Well, I know the bats - white nose is a problem that, I guess, that they have, and I know that's been hitting the New York populations fairly hard, like a lot of their populations in the Northeast.

FLATOW: Yeah. Okay. Yes, sir.

MEZOR(ph) (Caller): Yeah. My name is Mezor. I'm from Buffalo, New York. And I was just curious if you guys study non-native species migratory patterns, and if that compares to native species like (unintelligible)…

FLATOW: Give me an example of a non-native species.

MEZOR: Well, I've been seeing a lot of starlings in the Buffalo region, a whole lot of starlings and a lot less robins. And I was just curious why.

FLATOW: Yeah. Gentlemen?

Dr. BONTER: That's an interesting question and a tough question, I think. So, these non-native species that you're talking about are birds that have been introduced from another country, basically. So, a European starling, the traditional pigeon, rock pigeon that you see around cities, house sparrow, these are all non-natives.

Of those three, starling is absolutely a migrant. It's a diurnal migrant, so we see it during the day quite frequently, and sometimes in tremendously large numbers. It's a migrant where it's native in Europe. And whether there's any relation between that and some of the other patterns that you may see, I suspect not too much other than that they're obviously in the airspace at the same time.

FLATOW: Mm-hmm.

Dr. BONTER: But you absolutely see these kinds of patterns of a non-native species that clearly never occurred here or maybe rarely occurred here naturally, behaving as it does in its native habitat.

FLATOW: Let's go to the phones - to Jay in Sparrow Bush, New York. Is that real true Jay, Sparrow Bush on the show today? Jay, welcome to SCIENCE FRIDAY. Jay, are you there?

JAY (Caller): Yes.

FLATOW: Go ahead.

JAY: Yes. Speaking of robins, I had a couple of robins nesting on my porch this summer, and I wanted to know, you know, some of their behavior patterns that I experienced was that - they built two nests on the porch, and they used one first, had a litter, and then those flew away. And then they used the second nest. Now, I wanted to know, do they migrate in the winter, they - because I noticed that - I think that all the babies are still here, and they're like young robins now.

FLATOW: All right, let's find out. David?

Dr. BONTER: People in the Northeast seem to think that robins are really great sign of spring, but in reality, they are around all winter long. They move around. They form flocks and they move around in search of fruiting shrubs because they mostly eat fruit in the wintertime.

And these flocks of robins will go around and strip all the fruit from an area and move on. So they're not necessarily migrating in the traditional sense of going from a breeding ground to a wintering ground. But they're sort of moving around on this nomadic flocks in the wintertime.

FLATOW: Here's a tweet that came in from someone in Bird Diva, who wanted to know what kinds of skills could one learn to be better prepared to volunteer for citizens science projects? Are there bird-watching projects like this that citizens can get involved in?

Dr. BONTER: Yeah. There are all sorts of wonderful programs the people can become involved in and help scientists better understand what's going on with bird populations. And we run a lot of those at the Cornell Lab of Ornithology. Project FeederWatch is a great one, eBird, the Great Backyard Bird Count. You can go onto the SCIENCE FRIDAY Web site actually and find the link to a lot of those citizen science programs that really involve the public in helping us better understand what's going on in backyards all across North America.

FLATOW: Mark Deutschlander, do you have any…

Dr. DEUTSCHLANDER: Well, and if you want to learn bird banding, you need to find an observatory close to you, but…

FLATOW: But that's a real skill. You really have to know what you're doing, right?

Dr. DEUTSCHLANDER: Yeah. Absolutely. Periodically we offer training courses. Some people can come and get trained in those skills, but practice makes perfect, so you really need to work at it for awhile. And we have about 50 volunteers at our observatory alone who come on regular basis.

FLATOW: That old Carnegie Hall joke. Let's go to the audience right here. Yes?

Unidentified Woman #5: So the birds that don't migrate during winter, what makes it so that they can stay during the winter and not, like, die or anything?

FLATOW: She's going to be a scientist. Do you know how I can tell? She starts a sentence with the word so.

(Soundbite of laughter)

FLATOW: Very good question. Answer her question.

Dr. DEUTSCHLANDER: The answer is simply food. So birds migrate really in response to food or depletion of food. And if there is food available -actually there are birds that used to migrate that won't migrate or don't migrate now because there is food available for them. So as long as there's food, they can be fine. They can survive the cold temperatures.

Dr. BONTER: And most of these birds that are flying long distances eat insects. So they leave the northern areas in the wintertime because there aren't as many insects around. But the birds that stick here all winter long tend to eat seeds.

FLATOW: So if you're a migrating bird, are you resting during the day and at night you'll pick up again, you rest during the day and you feed during that time when you're resting?

Dr. BONTER: That's right. You try to maximize your feeding. These sites where nocturnal migrants stop over ideally have a lot of insects, have a lot of resources for them to take advantage of it, if they can stay there for a few days. For example, if conditions are not good, then they may be able to really bulk up.

As Sid was saying before, these birds have the ability to double or triple their body weight and prepare themselves for migrating these long or short distances. So any time they can get lots of food, they're going to do it. And doing it during the day is key.

FLATOW: Sid, how are these birds who are migrating know if the weather is good to fly out? How would they know that they're not going to be flying into a storm? They haven't got the - well, your radar to help them look at it.

Dr. GAUTHREAUX: Well, occasionally they do fly into storms. That's the tragedy. And there have been cases where birds miscalculated the strength of a cold front and exhausted their fuel supplies while flying across the Gulf of Mexico, and hundreds of thousands of them perished. On offshore oil rigs they had to get salt water hoses to hose the corpses off of the surface of the rig.

So sometime the mortality is incredible, but the remarkable thing is, is that the birds gain enough by flying across the Gulf that that trait survives. You know, if birds met that kind of destruction on a very regular basis, you wouldn't have trans-gulf migration. But the benefits of trans-gulf migration are immense. In basically less than 24 hours you can leave Yucatan Peninsula in Mexico and arrive on the northern Gulf Coast.

If you were around of the Gulf, you would fly at night, not during the day because of predation and turbulence in the atmosphere and the like, and it would take you four to five days longer. In migration in the spring, the rule is early bird gets the worm. It could be best food area, best territory or best mate or whatever. But the fact of the matter is, if you delay just a few days, it can cost you in terms of your reproductive success. So birds really optimize their schedule. They minimize the time in migrating to get to the breeding grounds as quickly as possible.

FLATOW: Wow. Interesting. Yes, sir.

Unidentified Man #5: Earlier on the program, we talked about, or you talked about the impact of life on the flight paths that the birds choose, and then a little later about the interruption of air traffic by birds and some of the things that are being used to detect that, the birds in flight. Is there any possibility of using light to somehow trick the birds into not going as close to the airplanes that are taking off?

FLATOW: Sid?

Dr. GAUTHREAUX: Well, the issue with that, a Russian colleague, Jacobi(ph), at one point thought that turning landing lights on aircraft actually scared birds away, but the evidence in support of that is pretty weak and in fact there's evidence that would suggests that turning these lights on may actually mesmerize the birds and cause them to fly toward the plane.

And so, again, that area in terms of whether you turn your landing lights on, when you're getting ready to descend through the layer of migrating birds at night in a spring and fall, that's still an active area of research. I don't know that anyone that would be willing to make a recommendation of do it or don't do it at this point.

FLATOW: Let me - thank you. Let me go to this side of the audience. Yes?

Unidentified Man #6: My question is, is when - instead of putting tags on the birds, why don't you just put like a microchip?

FLATOW: There you go. You see? You're talking 19th century technology. He's talking 21st. Yeah?

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Dr. BONTER: We actually do put microchips on the birds. The big problem with a lot of the small birds, though, is that a lot of the radio tracking technology requires a battery, and batteries are heavy. If you put something heavy on a bird, it's not going to fly. So a lot of the smaller birds, we don't have the options that we do, but people do put, say, GPS units on the backs of bald eagles to see where they're moving, so that does happen.

Dr. GAUTHREAUX: And even in small birds, David, they put geolocators, which are small chips that measure daylight. And we can't get very precise location information from these geolocators, but we can tell the latitudes because of day length that the birds are traversing. And so far that's provided some really intriguing information. Would the Russians, for instance, that are tagged in Maryland and so forth spend a fair amount of time in southeastern United States and then very quickly move to the tropics? And that stay in the Southeast is probably where they're putting on a fair amount of fat for the rest of the journey.

FLATOW: So you don't think that someday you'll shrink it down small enough? Andrew?

Mr. FARNSWORTH: I think that actually we're getting to a point now, especially in the last five years and probably in the next five years, where we see this technology become more and more useful because they are getting smaller and smaller.

Right now, as David was saying, we may be limited to a certain suite(ph) of birds on which we could put these transmitters. But in the coming years you're going to see it on very small bodied birds that are smaller than a robin or smaller than a house sparrow, and that's when we're going to start to get some incredibly important information like Sid is talking about, about where some of these birds are going. There are some species where we really don't know where they're spending the winter. We know where they breed.

Mr. FARNSWORTH: But this kind of information from these electronic tags is going to be really valuable.

FLATOW: Talking about bird migration this hour on SCIENCE FRIDAY from NPR News.

We're here at Cornell University in Bailey Hall in Ithaca, New York. A question. Yes, sir.

Unidentified Man #7: Yeah. I was wondering if you could talk about migration from an evolutionary standpoint. Why did birds start migrating? Why do they continue to do it?

Dr. BONTER: Well, some of the birds that we think of as our birds, as our northern birds, are actually related to birds from the tropics, so they've actually migrated out of the tropics to exploit the seasonal resources for breeding in the tropics. In the winter, it's fine, but in the summer, the birds that are resident down there are breeding as well and there's just not enough food for those birds to all breed. So a lot of the birds that come up here are coming, from an evolutionary standpoint, from the tropics rather than coming from the North down to the South.

FLATOW: Oh, and joining us now is Flora Lichtman. I'm going to bring her in a little early, our Video Pick of the Week. And Flora did take a trip out to the bird banding station, right?

FLORA LICHTMAN: Yes, that's right.

FLATOW: Tell us about what we're going to see on the Video Pick of the Week on our Web site.

LICHTMAN: Well, David Bonter was - one of our panelists was kind enough to take us to Braddock Bay. And let me set the scene for you because it's kind of amazing. You go in to this beautiful spot on Lake Ontario and there are these huge nests that are set up, but they're really fine so you can barely see them.

And then at sunrise, on the half-hour, volunteers from all over, as far as I could tell, and you know, David can correct me as I get things wrong - this troop of volunteers goes out for net checks and is sort of walking by these little nests and then retrieving these tiny little songbirds and putting them into these cloth bags that they wear on their necks. It's very - I mean…

FLATOW: It's beautiful.

LICHTMAN: It's beautiful.

FLATOW: You have video - you went out there and you videoed this and it's really beautifully edited and photographed. And you see the whole process that goes on there.

And how - and these birds are sort of - they're very peaceful as it's happening. I'm very surprised, they sit there and allowed this to happen. And Flora, you showed us how they did this and they are wearing these birds around - these bags of birds around their necks.

LICHTMAN: I thought this was the most amazing thing, actually how kind of cool with it the birds were.

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LICHTMAN: There was not a lot of squawking, actually, kind of surprisingly, I thought.

FLATOW: Yeah.

Mr. FARNSWORTH: The birds are on their way after being in hand for 15, 20 minutes tops, so it's a little interruption in their day. But as Flora says, it's really remarkable how most of the birds just look at you, like, yeah, this happens every day.

FLATOW: And there's a little blue - and there's a little reward of a blueberry patch out there.

(Soundbite of laughter)

FLATOW: They get to eat a little something.

Mr. FARNSWORTH: Yeah.

FLATOW: Like the doctor's office you get a lollipop - have some blueberries.

LICHTMAN: Yeah. It's a great spot for eating, is what - is what we heard, that it's like a full service restaurant.

FLATOW: And so you're happy, you went out there, and we've got this up on our Web site. And you can watch the whole process. And they go and they measure the wingspan and things like…

LICHTMAN: Yeah, and the bones. And I think one thing that also really surprised me is just the technique that these sort of citizen scientists learn. So if you take your hand, think of holding your hand in front of you and the bird's head sort of goes between your first and third finger, and then you have your thumb wrapped around it. And once it's in that position - I even got to hold on, which was thrilling - they really are pretty common, relaxed.

FLATOW: But you also show that you really need to be trained. Isn't that something…

LICHTMAN: No, I don't…

FLATOW: You really need a lot of training.

LICHTMAN: I don't think you can go just, like, snatch a cardinal off of your tree and do that.

(Soundbite of laughter)

LICHTMAN: (Unintelligible)

FLATOW: And you need the special tools like that little crimper tool that they put the banding…

LICHTMAN: Yeah. Actually, my favorite technique - my favorite measurement was the fat - figuring out how much fat the bird has on it. I mean, even maybe David could describe that quickly.

Dr. BONTER: Yeah. The fat is the fuel that powers their migratory flight and they store the fat in the abdomen, about where a wishbone is on a turkey. And their skin is pretty transparent, so you can actually blow the feathers apart and see this - either this empty cavity or this bulging mass of yellow fat that the birds are carrying.

FLATOW: Well, if you want to see all of this, it's on our Web site at sciencefriday.com on our Video Pick of the Week up there on the left side.

And I want to thank you all for taking time to be with us today. David Bonter, leader of Project FeederWatch at Cornell Lab of Ornithology, also vice president of the Braddock Bay Bird Observatory in Lake Ontario. Andrew Farnsworth is a post-doctoral research at that lab. Mark Deutschlander, associate professor and chair of the department of biology at Hobart and William Smith Colleges in Geneva, also president of Braddock Bay Bird Observatory. Sid Gauthreaux is professor emeritus in the department of biological sciences at Clemson University in South Carolina. Thank you all for taking time to be with us today.

Dr. BONTER: Thank you.

Mr. FARNSWORTH: Thanks, Ira.

Dr. DEUTSCHLANDER: Thank you, Ira.

Dr. GAUTHREAUX: Thank you, Ira.

FLATOW: Come back. You're welcome.

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