Podcast Official Draft

Pigeons are considered invasive, but their negative impact on native bird species is not well-documented, besides carrying diseases like avian influenza. Invasive bird species are more likely to reproduce quickly and be generalists in terms of their food and habitat preferences. The general public may not be aware of pigeons being invasive because they are common and resemble native species. Awareness of invasive birds as a whole is limited compared to invasive plants or insects. Managing invasive species is best done by preventing their establishment in the first place. Successful management stories often occur on islands where the invasive species can be completely eradicated. It is more difficult to control birds like pigeons due to their ability to fly and the risk of unintentionally harming native bird species. Hello everyone, welcome to another episode of Conservation Nation Station. I'm joined by your hosts, Maurice Artuso, Cullen Allen, Aaliyah Mayes, and of course, Nick Vandy. Today, we will be taking a look into pigeons. Today, we have Dr. Ellen Wisner, a professor at the University of North Carolina, 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. 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 size 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 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. 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, making it more likely that they get bird flu. So besides that, I'm not aware of a lot of other ways that they impact native bird species, but there's definitely, there's possibly some out there, but I'm not familiar with some of those other ways. Yeah, that aspect of pigeons carrying diseases, specifically bird flu, would definitely make sense as to how they are considered invasive. With that said, we also wanted to ask you, are there any behavioral traits that you're aware of that might make bird species more prone to becoming invasive? And 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 are 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, a generalist can do that. So yeah, I'd say those are 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 up 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 has a negative impact on native species. When you look at the USDA definition, it's broader. 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 outcompeting a native species. So to go along with what Dr. Weiser said about the public not knowing about pigeons being invasive, I believe Cohen has an article that ties together public knowledge of pigeon invasiveness and the urban environments that they thrive in. A 2018 article written by Shantang and colleagues discusses the correlation of human activities and pigeon abundance in Singapore. The article mentions that the model used in the study showed that pigeon density increased much more dramatically with the increased mercy feeding in high-rise landscapes compared to low-rise industrial zones and open vegetation landscapes. The article suggests that in order to manage the population of pigeons, mercy feeding needs to be reduced and the urban landscape needs to be modified. Yeah, that's interesting. I can understand why they kind of fly under the radar in that way. So Dr. Wisner, do you possibly know of any success stories that you could share with us about restoring biodiversity after the introduction of an invasive species or about the management of any invasive species? So that's an interesting, but 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. 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. 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 like 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 want to catch them and relocate them somewhere, that would be basically, you know, it's not impossible. 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. I understand how poison as a method of eradication could be dangerous for multiple species besides pigeons. But there are other strategies we can possibly use that may cause a little less damage. I believe Cohen knows of one that mentions predation of pigeons. The strategy involves the northern goshawk. The northern goshawk is a species of hawk that is also adapted to live in urban areas. It is a major predator of pigeons in these areas. According to a 2020 article published by experts Merlin de Chaffa et al., urban goshawks are 3.64 times as likely to feed on pigeons than those in rural areas. Other statistics showed that over 40% of their diet was pigeons and does, which has increased over the years. This research provides a potential solution for controlling populations of pigeons in urban areas or releasing more hawks in areas of high population density. It definitely makes sense why pigeons could be so hard to get rid of in any region that they're invasive in. I believe we have learned so much about invasive pigeons and the difficulties surrounding getting rid of them. I want to thank our guest speaker, Dr. Wisner, for giving us knowledge on the situation. And thanks to our listeners for tuning in to Conservation Nation Station. Thank you and have a great day.