In this extended interview from Saving Species, Stephen Redpath from the University of Aberdeen discusses raptors, birds of prey that hunt during the daylight hours.
All legally proected species, raptors range from the size of your finger to 15 kg, feeding on anything from insects through to much larger animals.
What is the predator-prey balance like? Is there enough data to even examine the issues? Professor Redpath uses hen harriers as an example, discussing them and their red grouse prey.
Professor Stephen Redpath: A raptor is what is known as a diurnal bird of prey. So that’s a bird of prey that hunts and feeds in the daytime. So birds of prey is a general term for meat eating birds that have hooked beaks and powerful feet, and there’s a huge variety of species, about 500 species in the world that range from an elf owl which could comfortable sit on your little finger to an Andean condor which is about 15kg, so a huge variety. In the
Interviewer: So how do they fit in if you like to the landscape of the
Professor Stephen Redpath: So all the species from merlin up to eagle are predators, and they’re all part of that predation guild, and they sit on top of a food web. And the range of species that they feed on is huge. So a merlin will feed on small prey like meadow pipits and skylarks, whereas an eagle will take much larger prey. A hen harrier is a really beautiful species. So it breeds on the ground, which is quite unusual for a bird of prey, and the male and the female are quite different. The male’s a bit smaller and the adult male’s beautiful grey with black wing tips, whereas the female is slightly larger and is brown with a white rump. And they float over the moorland. They mostly breed on the moorland in the uplands. They float over moorland and pursue their prey and pounce on their prey from quite close range. And the other thing about hen harriers is that whereas most birds of prey are monogamous, hen harriers can be polygamous so one male can have several females breeding close together.
So there’s a huge variety in the impact that birds of prey have on their prey species. So in many instances the birds of prey will have a very limited impact because the density of predators is so low and the density of prey is so high, whereas there are certain instances where predators can limit their prey availability.
Interviewer: Can you give me an example of some of those?
Professor Stephen Redpath: Yes, some of the work that I've done on hen harriers shows that they can have quite a big impact on the availability of red grouse. Hen harriers are unusual. Many species of bird of prey are territorial, so the densities don’t get particularly high, whereas for a hen harrier they’re not so territorial, they can form loose colonies. And the levels of predation can be quite high so they can actually limit the grouse populations. And in the case of grouse shooting they can make grouse shooting economically unviable in the worst cases.
Interviewer: Can you be a bit more specific about that?
Professor Stephen Redpath: So in studies that we’ve done the hen harriers could be taking one grouse chick every two to three hours. So when red grouse are really available then the harriers can selectively kill their chicks yeah.
Interviewer: What other birds of prey have direct effects on birds like red grouse or hares or partridge or whatever else?
Professor Stephen Redpath: The evidence suggests that peregrines can have quite a significant impact in certain instances. But for other species there just really isn’t the evidence there at the moment. So there’s lots of debate at the moment about the impact of buzzards on pheasant shooting, and lots of discussion about whether buzzards can have a big impact on pheasants. But the actual, the scientific data really isn’t there to be able to assess whether they do have an impact or not. In fact the science that’s been done suggests the impact is fairly small.
Interviewer: It’s interesting, isn’t it, because many people will be incredibly aware of buzzards now they are so much more common than they used to be, and even so that increase in numbers doesn’t seem to be having an effect yet that we can see.
Professor Stephen Redpath: Birds of prey are all legally protected and that legal protection has led to huge increases in the populations of lots of our birds of prey. And yes, you do see buzzards everywhere. There’s tens of thousands of buzzards in the country now, which is fantastic, but there is the perception that those predators must be having an impact on their prey.
Interviewer: But that perception as yet isn’t backed up by science.
Professor Stephen Redpath: That’s correct. There’s no clear evidence at the moment that buzzards have a big impact on pheasants.
Interviewer: It must be easy to then look at a bird of prey – it’s big; it’s obvious; it’s a predator – and almost assume it’s to blame.
Professor Stephen Redpath: If you’re out in the countryside there’s a general tendency to, if you see a predator kill a prey species then you think they must have having an impact on that prey species. But that’s not necessarily the case, because it depends on how many predators there are out there, what diversity of prey they’re feeding on and how quickly those prey can reproduce, because if they can reproduce quickly then they can compensate for a lot of that predation.
Interviewer: There is inevitably, as everyone knows, a lot of conflict at the moment. We’re hearing very often about illegal shooting or poisoning or trapping of birds of prey: the eagles, hen harriers have had a terrible time in
Professor Stephen Redpath: Different organisations, different people in society have very different views about birds of prey. So some people view them as tremendously exciting things to see in the countryside and others view them as a threat to their livelihoods and their way of life. So there are real challenges in thinking about how we deal with some of these problems in the countryside. And when it comes to some of the bigger conflicts, like the conflicts between conservation and game shooting, I guess there are really two ways of tackling it. And I think the community’s split about how best to deal with it.
So on the one hand some people say we need to focus on penalties and enforcement to try and catch gamekeepers who actually are going out and killing these birds of prey, and on the other hand you have people who are saying well maybe we should sit down and have some dialogue together and try and work out a solution to this problem, which we all share. From a conflict resolution perspective, it seems quite clear that the best approach would be to sit down and negotiate and find a solution that we can all live with. But that’s extremely challenging.
So I think it requires, probably requires four things. It requires good science to understand what impact those birds of prey are having on game. It requires time because these things take a lot of time and resources to do the research that we need. And ultimately it requires leadership. So it requires someone to take control of that dialogue process and to push through solutions and test solutions and see if we can get them to be, to find a solution that’s accepted to all sides.
To me ultimately what we’re trying to do is to get rid of illegal killing and to live in a countryside where we’ve got this diversity of approaches. But to find solutions that are acceptable to all sides, that allow us to have healthy viable populations of raptors and have game shooting.
Interviewer: Do you think that’s possible, do you think we can live with birds of prey without controlling them in any way, and still have healthy populations of other creatures?
Professor Stephen Redpath: The hen harrier’s virtually gone from
Interviewer: Because taking the very scientific approach may not always work, I mean a lot of the attitudes may be generations old if you like, so there’s a lot of culture behind it, not just science.
Professor Stephen Redpath: A lot of it is to do with values, and the values people hold and the threats they perceive from raptors and what raptors represent. But when I talk about science I’m not just talking about natural science; I’m talking about social science to really understand how the keepers feel about these things and trying to find a solution that’s acceptable to them that fits in with their values. Is there a way we can have hen harriers that’s acceptable to gamekeepers and acceptable to the conservation organisations?
Interviewer: Let’s talk about Langham for a minute, I did talk to Adam Smith who gave me a very interesting summary of what they think is happening there, and so supplementary feeding of hen harriers has, or diversionary feeding I think he called it, has certainly reduced the number of grouse they take, but what they’ve realised is that wasn’t necessarily the problem in the first place. Grouse numbers and wader numbers are not coming back in the way that they would have expected. So they’re now looking they think towards buzzards and ravens as being the main predators. So it’s quite a complicated situation in Langham.
Professor Stephen Redpath: So Langham is more in the South of Scotland, just north of the border with
So we did all that work and at the end of that project in the late 90s we then did an experiment to test whether if we fed hen harriers they reduce the number of grouse they ate. And they did, it’s fantastic. So if you feed hen harriers they’ll eat almost 90% fewer grouse chicks. So it was quite a big impact. But one of the questions was well if I feed hen harriers on my grouse moor, does that mean I’m going to end up with lots and lots of hen harriers coming to breed on my grouse moor because it’s obviously a really attractive place? So that was why a second experiment was set up with this current demonstration project to test whether if we have hen harriers and we feed them, whether we can have those predators and have driven red grouse shooting.
The problem has been that there’s so few hen harriers around at the moment in the North of England and the South of Scotland that harriers numbers just haven’t increased, so it’s very hard to actually test that problem. On the other hand red grouse numbers haven’t increased, so they’ve stayed below the level at which you can shoot, and there are various hypotheses for that. So one might be that there’s predation by other predators like buzzards; another hypothesis might be that the habitat is insufficient to hold high densities of red grouse. So those are the two hypotheses that project is now exploring.
Interviewer: One question that comes to my mind that hen harriers make driven grouse shooting uneconomic, isn’t that because you just need an unnatural number of red grouse on a grouse moor in the first place? Is it not an artificial situation that you’re putting hen harriers into?
Professor Stephen Redpath: The aim of driven red grouse shooting is to maximise the number of grouse that your grouse moor can produce. So the grouse moors are managed intensively to produce lots of wild game. So the heather’s burned, the parasites are controlled, the predators are controlled, and in some situations the birds of prey are illegally controlled as well. So the whole focus of it is to maximise the number of grouse to increase the grouse numbers.
Interviewer: Tell me about the lifecycle of a red grouse, what controls the numbers of red grouse naturally in a habitat?
Professor Stephen Redpath: Red grouse have got incredibly interesting population dynamics. By population dynamics I mean the changing pattern of numbers, the abundance of grouse over time. So if you go to grouse moors in different parts of the country you see that numbers can go up and down in a cyclic fashion. So you get these population cycles that appear. And that appears to be driven by two things, by parasites. They pick up these nematodes called trichostrongylus tenuous which lives in the guts and can get to very high levels which can actually kill the grouse. So that is one factor that causes cycles, and the other factor appears to be changing behaviour, so a change in aggressiveness. As population density builds up the birds become more aggressive and that drives the population down.
So those two processes cause these population cycles. The densities of hen harriers are not set by the densities of red grouse; they’re set by the density of smaller prey like meadow pipits and field voles. So you can get situations where you get very high densities of hen harriers and quite low densities of grouse, and that is where you have the problem because the harrier predation forces that grouse population into what is known as a predator pit, so it stops that grouse population from bouncing back.
Interviewer: Is there enough effort do you think being put into understanding this conflict resolution between people with different requirements out of the countryside?
Professor Stephen Redpath: I think we need to invest a lot more energy and resources into bringing people together to talk about these problems and trying to find a shared solution to these problems. We have seen it with hen harriers: there has been a dialogue group in
Interviewer: And who would that leadership, where would that leadership come from?
Professor Stephen Redpath: Well I would say that leadership has to come from government, so it has to come from DEFRA or from the advisers Scottish Natural Heritage in this country.
Interviewer: And can you give me an example of a compromise if you like that’s come out of this?
Professor Stephen Redpath: So one approach that came out of the dialogue process in
So we’re at an impasse at the moment where we’ve come up with a potential solution but we haven’t been able to test it in the field. So I think the conflict resolution approach is a strategy that definitely requires more energy and more resources to try and push it through, because I think that is the most likely approach to help us find solutions and move us on from these very contentious and problematic conflicts.
Interviewer: Are you hopeful?
Professor Stephen Redpath: I think it would be very helpful if we had a clear vision about what we want from the countryside. If you take the hen harrier example, what do we actually want in that hen harrier example? Do we want to have driven grouse shooting everywhere? Do we want to have lots of hen harriers, what is the goal? How many hen harriers is enough? What’s the conservation goal: is the conservation to have maximum numbers of hen harriers, to have a healthy viable population of hen harriers, to eliminate illegal killing? If we can come to some agreement about what that goal is then it’s much easier to find a solution.