How Are the Birds Doing?

00:00:00: Zurell: We actually have a lot of what we call extinction debt, so that we would expect based on the climate. For example, we would expect that a lot of species should be lost at a certain space, but the populations seem to stay longer, sustained longer. And the question is, when are those debts paid and the species vanish locally?

00:00:25: Hahn: Welcome to Inside Biodiversity. This podcast is hosted by idea of the German Centre for Integrative Biodiversity Research. My name is Volker Hahn. I am head of the Impact unit at iDiv. In this episode we're going to talk about birds. They are probably the animals we notice most easily in our everyday lives. We hear them in the morning, see them in our gardens and parks, and we generally find them quite likeable. But how are the birds doing? To answer this question, I invited Damaris Zurell to join me on the podcast. Damaris is a macro ecologist at the University of Potsdam and a frequent collaborator at iDiv. Her research aims to better understand, in her own words, why species are where they are, how they got there and how they may persist under ongoing environmental change. Much of Damaris research focuses on birds. So enjoy this episode of Inside Biodiversity. It seems that in conservation and monitoring, there's a focus on birds and maybe other species groups are neglected. Why are birds so popular among biologists and conservationists?

00:01:33: Zurell: Well, that's a really good question. Why are they so popular, actually? Actually, I also have colleagues who say, like, oh, birds, I don't want to study birds. So I think there are very strong opinions about it. What taxonomic groups? What species groups? People like. But birds are highly diverse. They are conspicuous. They have beautiful sounds. They have beautiful feathers. You can observe them anywhere in the world. I think that really contributes to their pendulum, if you want to say, and because they're so conspicuous. They're also volunteer citizen scientists who can study them very easily. And of course, from a scientific perspective, that is super important that we have really good long term data, long term monitoring data to study them. And they are one of the rare species groups where we have massive amounts of data. So this is also why we do a lot of studies on them.

00:02:31: Hahn: Is there a specific reason why you maybe focus? I mean, you're a macro ecologist, but I think you do a bit more on birds than on other taxonomic groups. Is that the reason? Or do you have another reason specifically for yourself?

00:02:45: Zurell: I just happen to work a lot with birds. Yeah, I've thought about it like, what is the reason? It's not. I'm not a classical ornithologist. I'm not really good field biologist, to be honest. So I'm not one of the, uh, bird counters, if you will. But I happen to work with birds for a long time now, so. And I do like them. So already before starting my studies, I was really fascinated by birds. I like seabirds quite a lot. My favourite birds are puffins and sharks, as well as of the North Sea coast of of UK, where I've experienced them a lot. Why I ended up working with birds is probably like a very winding story. So in my PhD I was developing a lot of methods and models and I just needed good data sets. So I ended up working a lot with the Swiss Ornithological Institute because they just had those wonderful data, the breeding bird atlases. And when you start working with a taxonomic group, of course you you get more into their ecology. You get a better system understanding. And then it's of course a very logical step sticking to it. And then in my post, my first postdoc, I worked on a more movement ecological project, working with migratory birds, white storks. And I found that absolutely fascinating that we have those migrants who really undertake long distance journeys twice a year. Somehow they know where to go, when to leave, when when to come, when to rest. And yeah, so they are also very personal reasons that just fascinate me. But often because we are so focussed on method development and my group on the one hand and on the other hand, answering large scale macro ecological questions, that also just makes birds a really wonderful case study for us.

00:04:50: Hahn: Well, many birds are so mobile and they migrate. It's also a reason why we have to look at them not only at the national level, but really on the global scale. And that's what we'll talk about today. How are the birds doing and how are metrics for bird abundance and species richness and so on? How are they changing? Let's first talk about abundance. In 2019, there was a study that called a lot of attention that said that in Northern America, within 50 years, the abundance. So the number of individuals in birds plummeted by 3 billion individuals. I don't recall the the percentage, but huge numbers. Can you tell us more? What do we know about abundance change in birds in the last decades?

00:05:38: Zurell: Yes. The most knowledge we have really comes from North American birds and European birds. These are just the regions where we classically have the most data because we had standardised monitoring, or at least long term Um, um, volunteer monitoring going on for a very long time. And indeed, the headlines from North America. They were massive, right? Like we had those big newspaper pictures saying 3 billion individuals lost. We have to see that this is the net loss. So that does mean that all of the species are declining, but there are a few species that are declining massively, actually, and 3 billion birds that since the 1970s that amounted to almost 30% of the individuals lost across all species in North America. So North America, we're talking, I think, about maybe 800 breeding bird species that occur there. In Europe we have similar numbers. So in Europe since the 1980s, around 600 million birds were lost. So that sounds a lot less. But we also have to be aware that. So that was just the European Union. And we have to be aware that the space, the region is of course, of course way smaller than the North America. When we express that as percentage number, then roughly 20% of individuals where lost. So also massive amounts that differs slightly. Again that's just net loss. So it means a few species have declined whereas others have actually increased. So the European study showed that it was out of roughly 400 600 billion bird species, there were around 170, I think, that were declining, but also around 200 that were actually increasing. But still overall, the individuals, the individual numbers of increasing couldn't counterbalance the losses. So overall we still had 20% of loss in individual numbers.

00:07:55: Hahn: Was it? Was that also because it was mostly the common species that declined more than the rare species, or at least some of them that actually increased? So that overall, if you just said look at numbers, then of course the net loss will be a loss. Maybe the broader question would be, what are the patterns of what types of bird are going down and which ones are going up?

00:08:21: Zurell: There are patterns. Um, actually so so for Europe, I, I've seen those numbers. It's quite interesting actually, that there were only eight species that made up almost 70% of the declines, and they were quite common. Right. So, so the house sparrow, the house sparrow, for example, was lost almost 50% of its population. And then there were other species that are still common, like the common starling, the Eurasian skylark. There are all species that that we all know. Um, but. And on the contrary, the species that increased, there were, again, just eight species that made up 66% of the largest increases in the European Union. And we can't say that all of them have been rare. So a couple of them are also quite common, like the Eurasian blackbird, for example. Others might have been rarer or might have suffered from from initial decreases. But, um, yeah, it's not only the rare species, we have rare species that have increased tremendously, especially among the larger birds, the birds of prey, but they have increased because of really strong conservation measures. Apart from that, we do see some very strong differences in which kind of Bird groups have declined. So in Europe it's mainly the the farmland birds that have declined by depending on the sources by 40 to 50%. In North America it's similar. It's the grassland birds that have also declined by about 50%, a bit more. The woodland birds have declined less in Europe, just 8% or by 8%, whereas in North America, the forest bird species, they also declined less than the grasslands, but it amounted to 17 to 30% or something, so more declines than in Europe. On the other hand, wetland birds, for example, have increased in North America and also in Europe. Waterfowl has increased. Not all wetland birds, right? Shorebirds have decreased, but waterfowl, for example, have increased. So we do see strong differences between between the habitats and also between the trophic level. For example.

00:10:49: Hahn: One observation, and it may be completely subjective of mine, is that many large birds have increased. Also, those living in wetlands like the crane or the white stork and the black stork, the eagle owl, the peregrine falcons, a rather large bird species. Is that just coincidence, or is there a reason for why large species increase? Maybe conservation measures? Or what do you think.

00:11:18: Zurell: It is definitely conservation measures here. So we can't say that on average large birds or large animals have a benefit. Quite the contrary. So so globally also when we look across mammals then we've seen the most extinctions in larger species, larger animals. And that was true for for the birds as well. And in these particular cases of the large birds that have increased its really strong conservation measures and also starting from a very low level. So first of all, we have to decrease those species to very, very low numbers because of various pressures. And now they're recovering from that. So you mentioned for example, the cranes and the eagle owls. They are really good examples for the common crane, for example, was really suffered badly from wetland drainage and hunting in the last century when I grew up in eastern Germany, in Brandenburg. So the area around Berlin, I don't remember the cranes very strongly from my childhood. But now Brandenburg harbours one of the most important populations in Germany. We have 30% of the crane population, 2500 breeding pairs, and that resulted from very strong protection of the wetlands, restoration of roosting and staging sites, but also changes in agricultural practices, and the cranes have now adapted to exploit the agricultural food resources. Um, the eagle owl is a similar example, where we've also driven the species to almost extinction in the 20th century. And then we have really large scale reintroduction programs, so that in the 90s we had around 700 breeding pairs in Germany, and now we have more than 4000. So so they're massive increases and same, same and white storks. So, so they've also profited from legal protection, reduction of illegal hunting um, improvement of or better protection of power lines. So mortality due to electrocution has decreased, etc. but but also for the white stork, for example, we see changes in the in the migration patterns. And that also has to do that. The species is what we would call a cultural follower. So a lot of the especially western migrating white storks, they are have have been exploiting landfills in Spain. So that means that they didn't have to to migrate down to, to Western Sahara anymore. But they actually overwintered in Spain. And for that reason they had a shorter journey. They lost less resources. They came back earlier from migration. And we believe that all of those factors contributed to their recovery.

00:14:30: Hahn: So we've talked now about Europe, mostly in Northern America. Do we know how representative what we observe in in these areas is for the rest of the world and what is actually going on in the much larger rest of the world, like in the tropics.

00:14:48: Zurell: That's a really good question. And the answer is no. We don't know as much in the other regions, and it's a big question how representative our data are. The problem is that we don't have similarly long term monitoring data in other regions of the world. We have them for very few locations. You mentioned the tropics. So there was a study over several decades from Panama where they looked at intact forests in Panama, and they actually found that the resident understory species there have also massively declined in abundance. So in 70% of the species, they found declines by by almost half the abundance. And we know from global reports. So so the biggest authority in the bird world is the BirdLife international that is running the red list updates and they have in the latest update from 2025. They have actually estimated that about 61% of all bird species globally have declining populations. We don't know how much, so we can't put similar numbers out for for the globe as we have for North America or Europe. We can't put it in numbers of millions or billions of birds, but we know that 60% are always strongly. We are strongly convinced that around 60% of the bird species are declining.

00:16:22: Hahn: I would like to switch the metrics. So we talked about abundance or the number of individuals. And how does that translate into the number of species. Species richness which we observe in different locations In the world. We've talked about this in earlier episodes of inside Biodiversity, oftentimes with many different species groups. We don't necessarily see declines in species richness. Sometimes we see increases and on average around zero, at least with the data that we have, which again has a bias in in Northern America and Europe. Can you tell us about local species richness in bird species?

00:17:07: Zurell: Yeah, I can try a little bit. So of course globally. But species richness is not increasing because that would mean that we have species evolving globally. We see that we do have extinctions locally. The picture is quite different. I was I was fascinated by by the different discussions you already had on the podcast about this biodiversity conservation paradox. And we see a similar pattern in, in, in birds obviously, that locally we don't always see Loss of species, but we also see gains. And that has to do, of course, with a redistribution of birds, reshuffling of of communities. So we do actually see a very strong turnover in in which species are present in a location or not. And again, the strongest evidence we have for North America and for Europe, I've also been involved in studies where we looked at how much have the the bird community shifted or the single species, and we actually found for European birds that they have shifted their ranges by. So single species on average shifted their ranges by 25km per decade over the last 40 years. And in North America it was even stronger. It was 35 kilometre per decade, not always northward. The European birds are shifting northward. On average, the American birds are shifting westward on average. But but that means they are switching their locations. And we have really local turnover of who's arriving, who is being locally lost.

00:18:50: Hahn: And is is that mostly driven by climate change or also land use change? Do we know that?

00:18:58: Zurell: That's very difficult to ascertain. So we we do find signatures that climate does play a role. And the it's actually increasing in pace. But of course there's also land use change and also other pressures. And when it comes to causation and really saying what are the causes of the different changes we see, whether that is in species turnover or also in abundance. That's much more difficult to say, but it's but it's likely a mix. We've done a recent study in North America and there we also see spatial differences that, for example, it seems like the range dynamics of the birds in the more western parts of us. For example, they carry a much stronger signature of climate change, whereas in the eastern parts of us it's more land use or a mix of climate and land use. But one problem also with with those pressures is that often we don't have exhaustive information about all the drivers. So when I say climate and land use, that just means that's the only driver data we had available and we could statistically analyse those two drivers. But that doesn't mean that the other drivers wouldn't have an impact.

00:20:19: Hahn: One of the important drivers certainly that is causing change is, um, climate change, but it's not necessarily loss in local species richness, and especially when I think of Europe and the Northern European countries. Climate change can actually increase the number of species in birds. This is what I learned from Susanne Fritz in an earlier episode of Inside Biodiversity. Whereas further south it may end. I have to say this is modelled future projections. So there's uncertainty involved there in southern countries in Europe, local species numbers might decrease. Is that something that we already are observing?

00:21:05: Zurell: Yes and no. So definitely as I said in Europe, we do observe that the species are moving northward on average. That means, of course, that we have like a net inflow of species into the north. And we don't yet see that too many species are being lost in the north. Luckily. But that I mean, that's just on average, right? When we really look into the spatial patterns, there's a lot of spatial variation also across Europe. Whereas when we look in the into the Mediterranean, of course we can expect that it's getting hotter and warmer. We have the heatwaves, we have fires. And that of course negatively affects the the species. Theoretically, of course, we have the tropics and subtropics. So there could be more species arriving also in southern Europe at some stage. But it doesn't seem to be the case at the moment. In the North, we will also lose species at some stage. But what we've found so far, by analysing the last 30 to 40 years of data, both for Europe and North America, is that we actually have a lot of what we call extinction debt, so that we would expect based based on the climate. For example, we would expect that a lot of species should be lost at a certain space. but the populations seem to stay longer, sustained longer. So. And the question is when are those debts paid? And the species vanish locally.

00:22:46: Hahn: So so new arrivals may happen faster than local extinctions of the species that. Were there before. But it's maybe become too warm. Is that right?

00:22:57: Zurell: Yes, yes. That's what we find for for the birds on average. So I mean we often. Say that species are, are, are responding dynamically to changes and they first have to arrive. Somewhere. So we can have different forms of, of time lags for example because of dispersal or. Because they don't go extinct instantaneously at a specific location in birds. What we found is that they are not that dispersal limited, but. The time lags we see is that they stay longer. Yeah, that. New birds are arriving. The others are not vanishing.

00:23:35: Hahn: Another widely discussed factor in biodiversity change is land use change. And I guess there are different facets of land use change, especially in Europe. One change that we're observing is that we have a land abandonment and maybe a recovery of woody areas, a decrease in agricultural areas. Does that partly explain some of the change we observe?

00:24:04: Zurell: It could definitely. Yeah. So a lot of the birds are specialised to specific habitats. We have forest birds. We have farmland birds. We have waterfowl for example. So if we have expanding forest areas then the forest birds might actually profit from that. And we have seen less declines in forest birds at least. Although as I said, it's not always easy to find exactly the causal effects. What's responsible for that? But we have seen more declines in agriculture. But even although we have land abandonment, land abandonment isn't always beneficial for the species. It really depends on the species. So some species do need some form of land use cultivation. Right. Like that. At least late. And so so the typical ground nesting farm and birds, they benefit from very late mowing events when when a field or a grassland is mowed very late in the year, that will determine how fast it will regrow in the spring and that will affect their breeding success, for example. So yeah, they have very diverse effects. It really depends on on the species and their habitat requirements.

00:25:25: Hahn: Can we put an order into the importance of different drivers on board change when we think of climate change, land use change, poaching. What else? Pollution. What are the the main drivers?

00:25:42: Zurell: It again depends on what metric we are looking at, whether it's extinction of species or species richness or whether it's abundance. I don't have all the numbers ready, but historically, of course, we can probably rightfully say that that it has been land use. And with that habitat loss and habitat degradation and direct exploitation that has led to to most declines and also to most extinctions. So direct exploitation means hunting and trapping. It also means fisheries bycatch for seabirds. And yeah, land use can be very diverse. As I said, it can be habitat loss. But but agricultural effects can also be more right. It's, uh. Yeah, but mostly they they affect the habitat. It can be removal of hedgerows that that affects the habitats of, of species that rely on that. It can mean changes in crop and mowing regimes, which again has influences on, on the, on the breeding habitats that can be drainage, which affects, for example, the birds that rely on wetlands like cranes. Yeah, it can be very diverse, but those are the two biggest factors. Land use and direct exploitation.

00:27:03: Hahn: It's very heterogeneous and it depends so much on on the species. And there are so many types of land use change and different effects of climate change. Still, can we say in general what should be done to protect birds? What is it that they need most? What can people who manage the land but also politicians? What what can they do globally?

00:27:29: Zurell: I guess what we need most is habitat. Not necessarily pristine habitat, but pristine habitat in the lens of the species. Right? Which could also mean it is managed habitat. It's just habitat that that really fulfils the requirements. So we can and because we have so heavily used a lot of the land, that inevitably means that we should protect forests and wetlands. We should restore forests and wetlands, we should try to maintain connectivity between habitats, even although birds are mobile. Right. And they're they're not as dispersal limited as other species. Connectivity of habitat is, of course, still important for habitat. Fragmentation is a big cause, and we can counteract that then reduction Of of any harms like illegal hunting is of course important. Reduction of harmful pesticides. Yeah. And we should also remember that this is. You said it at the beginning. It should be ideally it should be a coordinated international effort because a lot of the birds are migratory. So if we just protect the breeding habitats they the, the the numbers might still plummet because they are also relying on on staging sites during migration on the wintering side. So any protective measures really have to take place in coordination across different nations, different locations.

00:29:10: Hahn: What can someone who's not not working in politics or in land management, a normal consumer like I am? What can I do to help birds?

00:29:22: Zurell: Well, also, individually I think we can do a lot of things. So. So anybody who has a garden, I mean that this is where I would start. Um, ideally also there you would try to establish more habitats for, for the birds. Right. So, so that means have like a more heterogeneous vegetation cover in your garden, have native shrubs. This is quite important. Native shrubs, native flowers. They will also attract native insects. They will have seeds and berries that are important for for the birds and try to avoid pesticides. Then you can also increase the the nesting opportunities for the birds by by having nest boxes of course. Also there you should take care. What kind of nest boxes do I need? Should they be cavity nest boxes or should they be half open? That will benefit different birds. You should take care where they are. So so that they are not easily predated by or by cats or raccoons or anything. But, but these are things you can do if you have access to a garden. Or maybe if you're if your company has like a small area which where you could maybe influence something, then obviously the cat owners, one big thing they could do is not letting their cats roaming outside without a supervision, at least not during the breeding season. So keeping cats indoors or having secure outdoor enclosures, at least during the breeding season, can be quite important. Because although we love our animals, we love our cats. They also predate on birds, obviously, and.

00:31:11: Hahn: Quite large numbers. Right?

00:31:13: Zurell: Yes, yes. And yeah, other things like I don't know, try to to make very visible what our glass surfaces on the houses, right. That birds don't collide with glass. And actually having just some of those stickers on it might not be enough. So it must be a really sufficiently dense surface that the birds recognise that they shouldn't try to fly towards it.

00:31:43: Hahn: Yeah. Thank you. Uh Damaris. Is there anything that we should have talked about and that I forgot to ask, or that you would like to to tell us something we haven't touched yet?

00:31:56: Zurell: I think we covered quite a lot of aspects. Of course, I could talk for hours on the matter, but it's. I think we covered it quite well. Thank you.

00:32:09: Hahn: So my last question, what would you like the audience to remember from this conversation?

00:32:17: Zurell: A couple of points. Maybe first about the change itself. So ideally maybe the audience took away some of the numbers. Like we have birds that are declining. We have reshuffling communities also from like. Mirroring what you've already said in the previous podcast, it's not only about richness, but the picture is actually a bit more complex. Sometimes we don't have decreasing richness, but we still have massive changes in the communities. Then second point that this is related to multiple pressures. It's not always easy to put our finger on one source, but it's really a mix of human pressures. Climate change is increasing in importance, but habitat change, exploitation, etc. are historically really big aspects. Then we haven't. Like we've mentioned that maybe just on the fly, but monitoring is really important and I really like maybe that also relates to your previous question, what can everybody do? So everybody can contribute to to monitoring to citizen science projects. And we as scientists really appreciate all the data that that are coming in. And they help us to understand what is happening to the bird world.

00:33:35: Hahn: Is there an app that you would recommend to to report birds?

00:33:41: Zurell: There are multiple apps. It depends on where you are really. I mean, globally, I think what the Cornell lab is offering through through eBird, that is probably the most prominent. I think the app is Merlin where you can, uh, well, you can use it for identification, but you can also send your records in in Germany. We have different things. So you can, for example, through the Nabu, you can report birds, especially for the annual accounts of garden birds and the annual counts of wintering birds. So there are specific days in the year where you can contribute then the bigger ornithological societies. They also have annual bird races and in the German speaking area or in Central Europe. The ornitho app is also quite, quite relevant for reporting data.

00:34:35: Hahn: I will put those in the show notes for everyone. Okay. Anything else? Damaris.

00:34:42: Zurell: Um, maybe last point if you do want to help the birds, uh, like like look through the information you get from your local ornithological or conservation authorities. They always have nice information about when you should feed, what you could feed, and how you could help the local bird community.

00:35:07: Hahn: Thank you very much, Damaris, for this great conversation. If you enjoyed this episode, be sure to subscribe! Inside Biodiversity is available on all major podcast platforms.