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The Biology Of Birds Of Prey
Originally published on Fri September 28, 2012 3:30 pm
IRA FLATOW, HOST:
Up next, the biology of raptors, moving from giant animals to the birds, we're going to talk about here in Boise. Just outside of town is the Snake River Birds of Prey National Conservation Area. And that park has one of the highest concentrations of nesting raptors in the world, more than 20 different birds of prey, including golden eagles, red-tailed hawks, screech owls.
They all nest in or migrate around the area, and all that raptor activity has caused another migration. Lots of biologists have flocked to the area to study the birds. Boise State University is one of the only places where you can earn a master's degree in raptor biology. If you're listening and you want to become a master's in raptor biology, this is the place.
But why is it that the raptors like this place so much? And maybe my next guest knows. Maybe they do. Mark Fuller is research wildlife biologist for the U.S. Geological Survey. He's also director of the Raptor Research Center at Boise State University. And Julie Heath is associate professor of biological sciences at Boise State. Welcome to SCIENCE FRIDAY, both of you.
JULIE HEATH: Thank you.
FLATOW: Well, let me ask that question, whoever wants to answer: Why do the raptors love it here so much? Mark, you want to take that up?
MARK FULLER: Sure. Well, the area has two features that are very important to support the high densities. One, mostly due to the cliffs of the Snake River Canyon, there are many, many places for these birds to nest and be out of each other's way. And then on the adjacent plains of the Snake River Plain country, there's lots of vegetation and - prey and vegetation for them to eat and raise their young.
FLATOW: And what is the definition of a raptor?
FULLER: Well, in North America, when we talk about raptors, we- usually are referring to hawks, owls, eagles, falcons, vultures. In Europe, sometimes they separate owls out from raptors.
FLATOW: So does it have to do with whether the bird eats something alive or dead, or if it's eating something that they kill or something that's already dead?
FULLER: Mostly, they're hunters, and they capture live prey, although almost any of them will scavenge dead prey, and the vultures in particular rely mostly on dead prey.
FLATOW: Mm-hmm. And the common raptors that we find here are what? Name a few of the most common raptors.
FULLER: Well, the red-tailed hawk...
FULLER: ...the American kestrel, and the Birds of Prey Area in particular has a relatively high density of prairie falcons and medium-sized falcon and golden eagles. And that's part of the attraction for this area.
FLATOW: Well, Julie Heath, you specialize in studying a bird, the kestrel. That is the smallest bird, is it not, the smallest bird of prey?
HEATH: It's the smallest falcon, yes. Uh-huh.
FLATOW: Yeah. Tell us what you're studying about them. You've discovered some new things about their behavior?
HEATH: Their behavior and, in particular, their migration and breeding. I'm really lucky to be a part of a long-term monitoring project of over a hundred nest boxes around the Boise area. And what we've seen is that, over the past 30 years, kestrels are nesting approximately a month earlier than when we started the project. And that's a huge shift for a temperate species in their nesting phenology.
FLATOW: A month earlier.
HEATH: Yeah. Quite a difference from...
HEATH: ...you know, late April to now late March, is when they start.
FLATOW: And the reason for that would be what?
HEATH: Well, that's what we're working on. And, you know, nesting earlier in a time of climate change is not a new phenomenon. This is being reported all over the world, for all different types of taxa. The main hypothesis that's typically put forth is as springs warm and plants germinate earlier and insects emerge earlier, the animals benefit by tracking that earlier spring.
But what we think is going on in Boise, where we have not seen as many - as much warmer winter - or, sorry, as much warmer springs as we have warmer winters. So we think kestrels are not migrating as far as they used to, and they're staying closer to the breeding area. And this allows them to get the energy to breed earlier, and that's a huge benefit for them, because the first breeders do the best. They get the best territories.
FLATOW: Wow. This is SCIENCE FRIDAY, from NPR. I'm Ira Flatow, talking with Mark Fuller and Julie Heath. You're invited to step up to the microphone here in our audience and ask questions about the raptors we're talking about.
Mark, I know that, you know, of course, the fires have been burning all over Idaho. Are our raptor populations being affected by all these fires?
FULLER: To a degree, yes. On the Snake River Birds of Prey Area, there have been studies looking at the relationship between where the raptors nest and where they hunt, and where fires have occurred. And when the cheatgrass that we heard about earlier invades an area, it makes for a less diverse prey base, and it makes for a greater fluctuation in the availability of prey - dry years versus wet years. And this also affects - it affects ground squirrels, which the falcons eat, and jackrabbits that the golden eagles eat.
FLATOW: Hmm. A question from the audience here. Yes, ma'am.
UNIDENTIFIED WOMAN #1: Yes, sir. Dr. Fuller, kind of a follow-up to what you were just talking about, as you mentioned, some raptors will specify their prey base on birds or small mammals. Have you seen any evidence that raptors, as their prey base shifts with climate, that they are adapting to that?
FULLER: Yes. And both those species, they will shift and use a wider variety of prey when the less - the rabbit, the jackrabbits or the ground squirrels are less abundant. But usually, that means that there's less food overall, particularly food that they can bring back to the young and to raise their young.
FLATOW: Quick question here from this gentleman. Yes.
UNIDENTIFIED MAN #1: I'm curious. As an observer over the last 30 years in the area with my own theories, what's the status of the various raptor species in our area and their populations? Up, down, stable?
HEATH: Well, it depends on what species you're talking about and what time of year, and that's actually a really interesting question that we're spending quite a bit of time addressing because we think that they've - because our winters have warmed significantly, you've probably noticed also that we have much less snow cover in the winter. And for raptors, that's very important for their ability to hunt. And so, in the wintertime, we actually have a much higher abundance of the common species like northern harriers, rough-legged hawks that are - that typically winter here.
And then, in the spring, I'd say that most - well, some of the species in the canyon, the numbers of nesting birds have declined. But American kestrels, red-tails, Swainson's hawks, those have remained relatively stable.
FLATOW: So would you suspect that in other parts of the world, the same thing is happening wherever climate change is happening?
HEATH: Well, one of the toughest things with climate change is as animals change their biology, our ability to monitor their populations becomes really tough, because trends and, you know, trends and populations are counts. Do they mean a change in the population? Or do they mean a change in our sample as animals change distributions or change their timing of passing?
FLATOW: Right. All right, we're going to take a break, and when we come back, we'll talk more about raptors. If you'd like to ask a question in our audience, stand up there and let yourself be heard. Stay with us. We'll be right back after this break.
FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR.
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FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. We're talking this hour about the biology of raptors here in Boise, Idaho with Mark Fuller, research wildlife biologist for the U.S. Geological Survey, director of the Raptor Research Center at Boise State University. Julie Heath, associate professor of biological sciences at Boise State University.
And, Mark, let me give the next question to you. It's been now, what, 50 years since Rachel Carson wrote about DDT harming the birds. Have the raptors fully recovered? Is pesticide still a problem?
FULLER: Well, that particular pesticide, which has been greatly restricted in use in many parts of the world and banned, for the most part, in the United States, is not causing problems right now. There are some residual effects. We studied, for example, white-faced ibis that go to places where there still remains DDT in the soil. They eat earthworms, and they're still affected by it. Other species, by and large, have recovered, and that includes two species that were declared endangered largely because of DDT, the bald eagle and the peregrine falcon.
FLATOW: Mm-hmm. Let's go to the audience. Question, here.
UNIDENTIFIED WOMAN #2: Yeah, I was just curious. As someone who's lived in the south of Boise-Kuna area most of my life, I've seen the large influx of the raptor populations, and I've noticed pretty severe decrease in seeing of pheasants and quails and other non-predator birds. Is the large amount of raptors playing an effect on those other species that are not necessarily hunters?
HEATH: Well, I think that the raptors can take those types of prey. But probably the biggest effect in that area especially is not from raptors, but from land use change. So there's been incredible development of neighborhoods and loss of agricultural areas to development.
FLATOW: Thanks for that question. Yes, ma'am.
UNIDENTIFIED WOMAN #3: I know that there are a lot of falconers in Boise, and I'm wondering if you ever you have collaborative projects with falconers, or whether the raptor biologists and the falconers ever have something to learn from one another.
FULLER: Yes. In fact, falconers were, in large part, responsible for getting the recovery of the peregrine falcon underway. That's a long-standing relationship and a good example of cooperation. And I collaborate with falconers quite often, because they have various skills and experiences that I don't have. And so they can definitely contribute to our research.
FLATOW: Just a bit of information here, if I will: Is it falcon or falcon?
FLATOW: Or it's either way.
HEATH: Depends on how many martinis, I think.
FLATOW: I'll have to experiment with that and get back to you later.
FULLER: Well, you hear both.
FULLER: And Dr. Tom Cade at the Peregrine Fund, who's the person that initiated peregrine falcon recovery, would say falcon. I say falcon.
FLATOW: Either, either one. Yes, sir?
UNIDENTIFIED CHILD: What prey do raptors mainly depend on for food?
FLATOW: Great. Basic question. What do they eat? What do raptors - can you generalize?
HEATH: They eat anything that moves, right? Or if it used to move and now it doesn't anymore, they'll sometimes eat that, too. So birds, all types of birds, and all types of mammals - so rabbits and mice, rodents.
FULLER: And little raptors eat little prey, like insects.
HEATH: Although you'd be surprised how many small raptors also try to eat prey that are larger than them.
HEATH: Their attitude goes a lot (unintelligible).
FLATOW: And they move into big cities. In New York, we have raptors living among the skyscrapers.
FULLER: Yeah. Red-tail hawks and peregrine falcons, in particular, in New York. And here, there are studies to try and understand how suburbanization and so forth might be affecting the distributions of birds, how they adapt or don't adapt to our activities.
FLATOW: Mm-hmm. Let's see if we can get - well, one last question here, ma'am. Yes.
UNIDENTIFIED WOMAN #4: Kind of touching on the role of human impact, as you did with the pheasants and non-birds of prey, I was wondering what degree of impact, if any, exists due to sort of beneficial attributes of human development, such as transmission line proliferation across the Great Basin serving a role as perch points and allowing a larger area of prey, potentially, for raptors. Thank you.
FULLER: Well, I'll use a golden eagle as an example. It's a bird that many of us are studying right now to understand its population status. Power poles, like the large poles that go across the Birds of Prey Area, do act as perches. They also can be nest sites. And, of course, if there are perches, that gives the bird an advantage to hunt prey, a hunting perch, not just a resting perch. That's an advantage. Power poles also electrocute birds of prey. They are large size. They can cross their wings or touch different parts of wires and they get electrocuted. So there are pluses and minuses.
FLATOW: Thank you. And speaking of pluses or minuses - in the last minute we have - what about people who worry about wind turbines and wind mills for birds of prey?
FULLER: Well, that's one of the reasons that we're spending a lot of time looking at the golden eagle right now. It's a species that in a few sites is known to collide with the turbines, and it causes mortality. So we're trying to understand the extent of that - the particular circumstances of why it occurs in some areas and not others to better understand it.
FLATOW: I'm going to ask you to hang out with us a little bit because we're going to bring on another guest out. While you won't find him soaring over the Snake River, some California condors spend at least part of their life here in Idaho. The Peregrine Fund, that's a nonprofit group that works to conserve birds of prey, raises condors here. And the birds are released into the wild and other parts of the country. Chris Parish is the Condor Program director for The Peregrine Fund. He is talking with us from Vermilion Cliffs, Arizona, where they're getting ready to release some birds tomorrow. Welcome to SCIENCE FRIDAY.
CHRIS PARISH: Hello. Thank you, thank you. Quite a pleasure.
FLATOW: Yeah, you're welcome. I also want to bring on our multimedia editor, Flora Lichtman, who has visited with the condors here. Right, Flora?
FLORA LICHTMAN, BYLINE: That's right. Yeah, we made a stop there yesterday.
FLATOW: Yeah. And, Chris, are you getting ready to release a bird tomorrow?
PARISH: We are. We have three birds slated for release tomorrow. It'll be the first time that these three have been released. And we have annual releases. We release birds throughout the year, but we have a public release at least once a year to invite the public, a great opportunity for them come out and witness this endangered species recovery project for themselves. And, yeah, we will remotely open a door on the front end of our release pen at 11 AM tomorrow morning and give these birds their first shot at gracing the skies with the rest of their population here in Northern Arizona.
FLATOW: Well, why do the birds need help surviving? What's the problem?
PARISH: Well, I think like many species who are observed to be in decline, when you look a little deeper into their natural history and their biology, you'd find out some of those answers. And, of course, we found - through this experimental release in Northern Arizona, we found that some of the contributing factors are predation, which, of course, you would expect, their natural rates of predation. And then also, one we - maybe had an inkling of - from the prior studies, but lead poisoning from consuming the remains of animals that have been shot with various types of ammunitions, but - that have been shot with lead-based ammunition.
And these birds, being the scavengers that they are, they consume those remains containing small, minute amounts of lead sometimes, sometimes more. And because they're an obligate scavenger, they're very vulnerable to lead poisoning. So lead poisoning is probably our biggest cause of death. Well, it's our largest documented cause of death in these condors. And, of course, the good thing is it's something we can do something about.
FLATOW: Now, Flora, you were visiting, right, and you've got a first-hand look at the condors and the kinds of problems he's talking about.
LICHTMAN: Yeah, absolutely. So we went to The Peregrine Fund, which is right here in Boise, and it's like honeymoon hotel for condors.
LICHTMAN: I mean, the point - I mean, scientists call it breeding center. But the idea is to breed condors. These wild condors that Chris Parish is releasing start here. And I think they have about 60 condors there now, and 15 chicks were raised this year. And, yeah, we got a good look at two or three of the condors they have on public display, which are ones that are not going to go into the wild, while we were there behind the enclosure door, which was scary.
FLATOW: She's scared.
FLATOW: If you have a question here about condors or the raptors, please step up to the microphone. Don't be afraid to ask. Condors are not a pretty bird, I can see in your video, right?
LICHTMAN: I mean...
FLATOW: It's not the kind that people want to go and pick.
LICHTMAN: What's the diplomatic way to say it? They're striking. They're huge. I think it was almost hard to imagine when you hear a bird - hear about a bird with nine-and-a-half-foot wingspan, you know, I think that's hard to visualize. And then when you see it, they just look almost like cartoons. These are the mega vultures. They are the contemporaries of those animals that we heard about earlier, the saber-toothed cats and the woolly mammoth. And they're just - they look at of - they do look out of a different time. You should check them out on our website where we have the video.
FLATOW: Right. Yeah, it's our video pick of the week up on our website at sciencefriday.com, and it's really interesting, if you want to get in - get a close look at a condor. And you weren't allowed to get too close. Well, there's a big sign up there that says...
LICHTMAN: This is the amazing part. So Bill Heinrich and Ty Carvalho were the ones who took us around The Peregrine Fund. And right before we go in, Ty says, well, you know, these guys are made to rip flesh off the bones, so just be careful.
LICHTMAN: It was amazing. So we were sitting there sort of crouching, and Ty was there within that, ready to shoo them away if they dive bomb us, which apparently is a problem if you get in the pen with them. Although, I wonder if Chris Parish - do you have to be careful when you're working with these birds?
PARISH: You know, it's like any other type of wildlife. I mean, they're, you know, like most wildlife, they're goal is to get away from you. You are perceived as a threat. And actually, with condors, that's one of the problems as they don't have any innate fear of humans. And so that and their curiosity and their intelligence level sometimes gets them into trouble.
But, yes, when we have to go into a pen to a grab a bird, to get it in hand so we can pull a blood sample to determine whether or not it's been exposed to lead, for example, that season, then, yeah, when you go grab a condor, they're not too good with that. And, you know, you do it diligently and quickly and - yeah. But still, they're going to get you every now and again.
FLATOW: Yeah. How long do you - when you release then - I saw from Flora's video they each have a giant number on their wings. You know, it's like...
PARISH: That's correct.
FLATOW: And it's visible from quite a distance because it's a pretty big number. How long do you track them and how long do you expect - how do you know when it's successful, that they have taken over?
PARISH: You bet. I mean, our goal here in this reintroduction program is to result in a self-sustaining population. And because we have not reached that level yet - and that's not necessarily just a number. But at the moment, we're losing too many birds to causes of death - anthropogenic causes of death like lead poisoning, that we're not ready to take the handlebars off of the bike and let it ride yet because we want to be able to track these birds so that so if they should become sickened or if they should die, that we can recover them and determine why.
So we use that information in the feedback mechanism so that we can give that information to the people who can make a difference and then change, you know, a little bit of our behavior that are going to allow for a self-sustaining population. So it's a continual process, and I'm hoping sometime in the near future, maybe in the next 10 years, we can start removing those number tags and have some confidence by our day-to-day observations that they are going to make it.
FLATOW: This SCIENCE FRIDAY from NPR. I'm Ira Flatow with Flora Lichtman. We're talking with Chris Parish of the Condor - Condor Program director for The Peregrine Fund. Who has a question in the audience? Yes, sir.
UNIDENTIFIED MAN #3: I was just wondering what the approximate wild population of these condors is.
FLATOW: Good question. How many are out there, Chris? Do you know?
PARISH: Yeah. There are now over - oh, gosh. We just got an update here a week ago. Let me just put it under perspective. From 1982, when there were 22 individuals left, 22 condors, period. We are now over 400 total, over half of which are in the wild. Only - reasonably good at keeping tracking of our own population right now, but in Arizona and Utah alone, we have 75 birds. And I believe they are closer to over a hundred in California, spread among four different release sites, including one in Southern - in Mexico and Baja.
FLATOW: And how many were you responsible for?
PARISH: We are responsible for the 75 that we have in our population here. And a crew of six amazing biologists and a field manager, they basically keep tabs on the birds every day and alert us to the fact that something's happened or we need to trap the birds. And they are the ones out there doing it every day.
FLATOW: And how do you get a bird to take care of?
PARISH: We trap the birds the same was we trap all of you guys, although you didn't that you were trapped, did you? We lure you into an area and close the door. It's that simple.
PARISH: We use food as a stimulant, though. We draw them in with food and we accustom, you know, make them accustomed to an area and then ultimately close the door. And the adult, they become pretty savvy to that pretty quick. But the youngsters, boy, they see a carcass and they know its time to eat and they have - are pretty reckless that way. And because of the feeding hierarchy and when youngsters are feeding, usually the adults just can't stand it and they finally have to get in there and then we trap them as well.
FLATOW: Yeah. I was looking at Flora Lichtman's video, and she documented this very well. You talked about lead poisoning, and that comes from the lead shot from - that is killing the birds and - or just poisoning them slowly?
PARISH: Well, there are several different mechanisms of delivery into the system. But one is lead shot. And lead shot, of course, we know about from the waterfowl, the transition from lead shot to steel for the sake of waterfowl and the raptors that were feeding upon those waterfowl that contained lead shot. We have observed lead shot in condors, but the more common occurrence is, each year, in association with the large game hunting seasons where we use high-powered rifle bullets - high-powered rifles and those lead-based rifle bullets, those bullets, upon impact, fragment into the animals that are shot in. Those fragments can then be consumed if those remains are left available to scavengers.
And it's those small fragments that sometimes are so small, you barely even see them are those that are consumed by raptors. And it's not just condors, the obligate scavengers, also bald eagles, golden eagles, ravens and those things. And when they ingest that meat that has small shards of lead fragment, they become lead poison. Now, it depends on how many exposures in a row and of what magnitude, that's what determines how sick they become. But it's not that condors or other raptors are more susceptible to lead poisoning. It's that for condors, they're obligate scavengers.
So seasonally, they feed on those carrion, those remains of animals left in the field that have been shot. It can be a hunting situation. It can be domestic livestock that's put down. Anytime an animal is harvested with lead or is shot with lead-based ammunition and the remainder left in the field, the potential for exposure is there.
FLATOW: Well, you can see this on our video pick of the week. Flora's got it up there and you can see the - sort of the mark of what goes on with the birds and how the - there is an attempt of change over to copper instead of the lead.
LICHTMAN: Yeah, it sounded like hunters we're complying voluntarily. That's what I heard.
FLATOW: Yeah. That's good to hear. We've run out of time. Thank you all. I want to thank all of the folks who are here. First, Chris Parish, thank you for joining us. He's director of the Condor Program for The Peregrine Fund. Julie Heath, associate professor and biological scientist at Boise State and Mark Fuller, who is research wildlife biologist for the U.S. Geological Survey and director of the Raptor Research Center here at Boise State. Thank you all. Thank you, Flora.
LICHTMAN: Thanks. Transcript provided by NPR, Copyright National Public Radio.