Podcast Unofficial Draft

Dr. Ellen Wisner discusses the impact of pigeons as invasive species on native bird species. While pigeons are classified as invasive, there is limited information on their negative impact besides carrying diseases. Species with high reproductive rates and generalist traits are more prone to becoming invasive. The general public may not be aware of pigeons being invasive due to their widespread presence and resemblance to native bird species. Successful management of invasive species is challenging, especially on large continents. Eradication efforts have been more successful on small islands. The ability of pigeons to fly and the risk of harming native bird species make it difficult to control their population. Hello, today we have Dr. Ellen Wisner, a professor at the University of North Carolina at Charlotte who teaches a biology of birds class and who is an avid bird learner and enjoyer. Thank you Dr. Wisner for having us. Thank you for having me. So to begin today, we have a few questions on the basis of bird species and their interactions with native birds. To begin, I'll start with a question as how do pigeons affect native bird species and do you know any in particular that they might affect? Yeah, so this is an interesting question. When you all reached out to me to see if I wanted to talk about pigeons as invasive species, at first I was like, wait, are pigeons invasive? So there are invasive bird species and when I think about invasive bird species, I think about those birds that do have a huge impact on a native bird species. So maybe outcompete them for nest sites or outcompete them for food resources. And so when you all reached out, I thought, oh, well, do pigeons really fit that, is that part of what they do? And interestingly, I found that, you know, that pigeons are classified as invasive, but that I couldn't find a lot of information about them negatively impacting native bird species besides that they do carry some diseases. So things like avian influenza, that's something that they do carry. All birds carry it, but so I could see it's like the population density, like the number of pigeons that are high enough in an area, they could potentially impact native species by infecting them, you know, making it more likely that they get bird flu. So besides that, I did, you know, I'm not aware of a lot of other ways that they impact bird species, native bird species, but there's definitely, there's possibly some out there, but I'm not familiar with some of those other ways. We wanted to know, are there any behavioral traits that make bird species more prone to becoming invasive? And if there are, then how do those traits contribute to their success in new environments? Yeah, so with any invasive species, the things that make them more prone to being invasive are one, if they're able to reproduce quickly and have a lot of offspring. And so you are focusing on pigeons and they do have the ability to have a lot of offspring. I think they can have up to 12 eggs per year, which is like pretty high. They can reproduce up to six times per year. A lot of bird species reproduce once per year, maybe twice per year. So that's a fair amount for birds. Another thing that makes species more likely to be invasive is if they're more generalist species compared to like a more specialist species. So that would be a species that isn't super picky about like what it needs to eat or isn't super picky about the area that it needs to build a nest or something like that. And so those make good invasives because if they move into a new area, they will be able to capitalize on some sort of food that's already present. So thinking like in an urban area like a city, if a pigeon is able to eat seed, but also potentially like human garbage or human food that's left behind, that a generalist can do that. So yeah, I'd say those are the kind of the two biggest things that make species more likely to become invasive. Why do you think the general public might not be totally aware of pigeons being invasive? And do you believe that awareness of invasive birds as a whole is expressed to a good degree? So I mentioned earlier that I wasn't totally sure whether pigeons were invasive myself. And I was like, you know, I was wondering what the exact definition of an invasive is because I know what I think it is. So one of the things I did is I wanted to look at the exact definition of an invasive species. And when I look at my ecology textbook, the definition is different than what the USDA, which you know, the US government defines as an invasive species. So based on the ecology textbook, the emphasis is really on a non-native species. So a species that is not natively found in this area that gets to high population densities, which pigeons do both of those. But then the key in the ecology textbook is that it has a negative impact on native species. When you look at the USDA definition, it's broader. Okay. And it's broader because that last characteristic of it having a negative impact on native species, that's one possibility, but they also allow, like, even if it doesn't have an impact on native species, if it does, like, economic harm, then they include it in invasive species. So I think it kind of depends a little bit on what definition you're using. But I think there's a couple reasons why people may not be very well aware of things being invasive. First off, there are pigeons everywhere. And so a lot of people may not know that they're not native to North Carolina, for example. There are pigeons here, and people may not know that they're not native. They've seen them their whole lives. They look like a lot of our native species. You know, we have doves here that look very similar to a rock pigeon. And so they may just not be aware that they're non-native. And then the second part of your question about, like, are people really aware of invasive birds? I think they're less aware of invasive birds. And I think that's in part—they're not as many invasive birds as you see in a lot of other species. Like, when you think invasive species, people often think of, like, invasive plant species, because you hear about those more, or, like, an invasive insect that's maybe killing off things that we need. So I think people are aware of it less because we hear about it less. I will say that when I think invasive bird species, and, you know, I don't know about the public in general, the first ones that pop to my mind are the house sparrow and the European starling. And those two are kind of famous because they do have pretty negative impacts on native species. So that's kind of why I'm immediately like, oh, that's an invasive that's out-competing a native species. And do you have any success stories that you might want to share with us about restoring biodiversity after the introduction of invasive species or management of invasive species? So that's an interesting—it's a good question. So the best way to protect against invasive species is to protect from them originally getting established to an area. That is by far the easiest way to prevent an invasive species. That's why there's really strict regulations about, like, moving animals and plants across, like, country borders. And the idea is to try to keep invasives out. Now, once an invasive gets in an area, it is really difficult to manage. As we talked about earlier, they reproduce really quickly. And so when you have this species that's really good at reproducing, it's just hard to get rid of them. As far as success stories or management techniques, most of the more successful management stories that I'm aware of happen on islands. And they happen on islands because what the goal would be would to get rid of that invasive species completely from that area. If it's a relatively small island, that might be feasible, right? You might be able to go—if it's pigeons, you might be able to go find every pigeon on the island and get rid of it in some way, right? So however you're going to get rid of it. That is much more difficult when you're in, like, a large continent, because it's going to be more difficult to find all of those individuals. So I don't know of any with birds, but I know that in, like, in New Zealand and Australia and some of the islands around New Zealand and Australia, they have been able to successfully eradicate, so get rid of invasive mice species on several small islands where they removed all of the invasive mice from the islands. But again, I think it's really much more difficult when you are not on an island. A quick follow-up. Do you think for it being a little harder to control in general is because they are avian? Like, they have the ability to fly, so it's to a point where we cannot control them because we are not in the air. Does that just come—it comes down to that, would you say? I think that's a large part of it. The other thing that I think it would make be really hard to target pigeons specifically is, like, we have a lot of native bird species that are very similar to pigeons. And so let's say you're going to—I mean, this sounds bad, but let's say you're going to try to target the pigeons and maybe, like, use some sort of poison or something to reduce their population. There's a real risk that you could accidentally hurt native bird species, too. So I think that that is a real risk. And I think you're right, Nick, that their ability to fly makes it harder, too, because, one, they're harder to catch. If you wanted to catch them and relocate them somewhere, that would be basically— you know, it's not impossible, but it would be harder to catch all of them. And they can easily disperse to new areas. So because they're good at moving away from you, it would be harder to get rid of them.