University Place

Birds as Sentinels of Climate Change

– Welcome, everyone to Wednesday Nite @ the Lab. I’m Tom Zinnen. I work at the UW-Madison Biotechnology Center. I also work for the Division of Extension, Wisconsin 4-H. and on behalf of those folks and our other co-organizers, PBS Wisconsin, the Wisconsin Alumni Association, and the UW-Madison Science Alliance, thanks again for coming to Wednesday Nite @ the Lab. We do this every Wednesday night, 50 times a year. Tonight, it’s my pleasure to introduce to you Benjamin Zuckerberg. He’s a professor in the Department of Forest and Wildlife Ecology here at UW-Madison. He was born in Brooklyn, New York, and went to Packer Collegiate Institute for high school, and then he went to Connecticut College for his undergraduate degree in zoology. He got his master’s degree at the University of Massachusetts in Amherst, and then did his PhD at the State University of New York’s College of Environmental Science and Forestry in the city of Syracuse.

He then did a post-doc at the Cornell Laboratory of Ornithology before coming to UW-Madison. Tonight, he’s gonna speak with us about birds as sentinels of climate change. Would you please join me in welcoming Benjamin Zuckerberg to Wednesday Nite @ the Lab?

– Well, thank you Tom, for the invitation to come to speak with you today. And the topic I’m going to discuss is birds, and how they are important in potentially serving as this very important indicator and the sentinels of climate change. And so I’m going to begin my talk kind of positing an important hypothesis, that birds are awesome. And they are awesome really for a number of different reasons. One, that they are numerous. We have birds that occupy almost every different kind of habitat and ecosystem throughout the world, from the Arctic, to wetlands, to the tropical rainforest. And at the same time, they are incredibly diverse. You know we can walk outside and see warblers and kinglets, and we can also of course see eagles and raptors and owls.

And another important aspect of birds is that they show an amazing array of behaviors, from tool use, to the use of supplemental food, to being able to use novel types of habitats and shelters. And importantly, because of this behavioral sort of array, they can actually show pretty amazing adaptations and changes in response to environmental pressures and stressors. Importantly, birds also clearly play a very important role in our culture. They’ve infused themselves in terms of our song and our artistry, and we have well over 35 million people in this country alone who actively go out and feed their backyard birds, and many millions more throughout the world that go out and look for birds through bird watching. An important aspect of birds also is that birds have always served as important sentinels of environmental change. And some of the stories and lore of coal miners bring canaries into the mines in order to serve as that important environmental and health indicator that something is wrong in the mine. In fact, if a canary, let’s say, started showing signs of distress, then that was a good sign and indicator for the miners to evacuate that coal mine. Unfortunately, over the last 100 years, many of our sentinels are not doing particularly well. We’ve seen rising threats in the form of habitat loss and fragmentation, environmental pollution, and the use of insecticides and pesticides in the environments, over hunting and overuse of many bird populations, as well as the proliferation of domestic pets, as well as domestic pests that have infiltrated many bird populations with significant damage. So much so that over the last 30 to 40 years, we’ve seen roughly the loss of 2.

9 billion birds throughout the United States alone. Compounded all these different stressors and overlaying many of these environmental changes is of course modern climate change. And what we’re seeing here is an animation of global temperatures comparison to pre-industrial era of the 1850s to 1900 showing pretty remarkable change in the global climate system. In fact, what you’ll see here, starting roughly in the 1970s and early 1980s, is a pretty rapid and dramatic change in the Earth’s system, and a rapid warming throughout much of the Earth. There’s a couple aspects of this that I wanna really focus on, especially as it relates to birds. One is that the ubiquitous and uniformity of warming is widespread throughout the globe. There are very few regions of the world where we’ve seen a bucking of the trend, so to speak, where we’ve seen cooler regions, or regions that are not warming. This warming is so uniform and widespread that we’ve seen roughly about one degree warming compared to pre-industrial era of the late 19th century. Another important aspect of this is that those northerly latitudes, those northerly ecosystems of the northern hemisphere are warming at a rate that is anywhere from two to three times faster than what we’ve seen throughout the rest of the world. It’s an important aspect of this when we look and can reconstruct temperature data throughout the world, dating back the last 2,000 years, and it’s very clear that what we’ve seen in terms of changes in the late 19th century and in the early 2000s here is relatively unprecedented.

In fact, if we reconstruct data going back the last 10,000 or 100,000 years, what we can say is that this is one of the warmest periods that the Earth has experienced. What we’re seeing at a global level, we are also seeing here in the United States. So like the Earth, much of the United States is getting warmer. In fact, every decade has generally been warmer than the decade before it, going back to the 1980s. Some other areas that are getting warmer the fastest are absolutely in Alaska, the Northeast, and here in the upper Midwest. And like the globe, we are seeing very few areas that are showing a reversal or difference in that trend of warming. In fact, that warming hole that we can see there in the Southeast really only is one of the few areas that hasn’t warmed as fast, but what we are beginning to see is that warming hole is in fact closing, and now much of the warming in the Southeast is beginning to catch up. Another area or signal of climate change has been what we’ve seen in sort of changes in precipitation and rainfall. And part of what we’ve been able to document is that some areas of the United States are getting wetter, and some areas are getting drier. Places like the Northeast, in fact, are showing pretty strong changes and increases in rainfall and precipitation, and a higher likelihood of these extreme events, like flooding.

Parts of the upper Midwest, kind of a mixed bag. Some areas are seeing drought-like conditions, and some areas are seeing increases in rainfall, like here in southern Wisconsin. Parts of the west of the United States are showing what we know to be mega-drought events, where we’re seeing drought-like conditions that stretch for years, and in some cases, decades. At the same time, with all these changes in terms of temperature and precipitation, it is clear we are seeing unprecedented changes in carbon dioxide in the atmosphere. When climate scientists have been able to reconstruct carbon dioxide levels, going back 20 million years, we can see that the levels that we’re experiencing today are in novel and in uncharted waters. 800,000 years ago, and looking at the CO2 reconstructions, suggests we rarely got above 400 parts per million. And now the current level is about 413 parts per million. When we look at the changes in carbon dioxide in the atmosphere under different scenarios, as you can see here with these different lines, even the best case scenario, that orange line, suggests we won’t go below that 400 parts per million line over the next 100 years. And under the worst case scenario, in terms of that purple line, we’re seeing that carbon dioxide levels are likely to double due to human emissions. An interesting experiment is what’s referred to as a pulse experiment, and the idea here is that if we were able to basically burn all the fossil fuels that we’ve already taken up out of the Earth and are now existing in our car tanks, what we would see is that the CO2 levels would rise to roughly 2,000 parts per million.

It would take roughly about 1,000 years for those levels to start going down. So at the same time we’re seeing these changes in rainfall, temperature throughout the world at an unprecedented rate, we’ve seen these concurring changes in carbon dioxide due to human fossil fuel emissions. Taken together, all these lines of evidence tend to point in the same direction. We are seeing CO2 concentration levels at the highest they’ve been in at least the last two million years. We’ve seen sea level rise at the fastest rate in the last 3,000 years. And we’ve seen changes in Arctic sea ice that is at its lowest level in at the last 1,000 years. And we’ve seen a glacier retreat that’s relatively unprecedented over the last 2,000 years. All together, the signals come together and suggest that it is unequivocal that human influence has warmed the atmosphere, ocean, and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred. So the question I’d like to talk about today with you is this overarching set of questions of how birds might actually respond to these changes in temperature, rainfall, and other factors.

Ultimately, birds have three different choices. They can one, move, and we can certainly see that. Birds are highly mobile, they’re vagile, they can move great distances, and clearly one aspect or pathway for them to respond to these new changes is by movement; moving to new areas and tracking their climate space over time. Or birds can sit where they are and stay where they are, and ultimately adapt. Perhaps they can change, use new food resources, perhaps they can adapt to a new climate, and essentially stay where they are. But if a bird and a species cannot move and/or adapt, then ultimately, they face extinction. So for today, I’m gonna walk you through a few case studies and stories. I’ll talk about how birds might be responding to climate change and serving as these important sentinels. I’m going to talk about bird behavior and changes in behavior. I’m gonna talk about range changes and how they may be shifting their distributions over time.

Phenological changes, and the timing of reoccurring events like migration. The conservation concern of population declines, a response to climate change. And ultimately, one of the main concerns is the emergence of infectious disease that can influence multiple species and impact populations across multiple regions. So first, the question of behavior. One of the areas and times of the season that I’m particularly fascinated about in terms of how birds respond behaviorally to climate change is winter. And winter is changing rapidly throughout much of the northern hemisphere. In fact, if we look at snow cover extent, going back to the 1970s, we can see that there has been a pretty marked decline in snow cover and seasonal snow cover throughout the northern hemisphere. Really, going back to 1980 and continuing from there on. These changes, especially during the transition from winter to spring, have resulted in the loss of roughly four million square kilometers of seasonal snow cover. To put that in perspective, that’s basically losing an area the size of Texas per decade.

If we conceive of snow as habitat, just like we might think about tropical rainforest, well, we can clearly see this as a form of habitat loss that rivals anything that we see throughout the world. And what we’re seeing globally and at the hemispheric level, we’re also seeing here in the state of Wisconsin. We’ve seen changes in snow pack of upwards about 20 to 15 days fewer since 1970, in terms of persistent snow pack in the state. So much so that the peak of winter has now shifted from February to January. So this leads to a question of how might birds respond to this changing winter landscape and environment? Ruffed grouse are a perfect example of a species that is emblematic of the northern forests of Wisconsin and the upper Midwest and has a distribution that’s into boreal Canada, and meets its somewhat southern range boundaries and distributional limits here in the upper Midwest and down the Appalachians. This is a bird that is clearly adapted to the winter environment. It is not a migratory species like we see with spring migrants, and they have to really be able to take advantage of that winter environment and display a number of unique behaviors to allow ’em to get to that very strong sort of winter and snow-covered landscape. One of those behaviors is seen here. – Man: Can we move forward? – Woman: Yeah, you can try to. [wings flapping] – So what you just saw was a really unique behavior that ruffed grouse show; it’s called snow roosting.

So like a lot of different birds, especially during the winter, grouse will use this roosting behavior almost about 80% of the time to conserve their energetics. And they can do this roosting behavior on the ground. Like other birds, they can roost up into trees, but unlike other birds, they’ll actually roost into snow, and they’ll do this in a couple different ways. They either create these snow bowls, which they’ll kind of burrow down into the snow and kind of encapsulate themselves in this little bowl in the snow, or in some cases, they’ll fly up into the air and dive bomb underneath the snow and create a snow cave. So these snow roosts have a couple of advantages if you’re a grouse trying to survive the winter. One, you can avoid predators. If you’re a grouse and you’re hiding underneath the snow, there’s probably less likely a chance that you’re gonna get picked off by some kind of owl or a raptor. The other real advantage, however, is temperature. And if we look at temperatures that a grouse is experiencing in the snow roost compared to the ground, well, they’re almost seven degrees warmer if they burrow underneath the snow. In this case, you can imagine that the snow is basically serving like a snow blanket, and keeping a very sort of stable thermal environment that the grouse is taking advantage of.

One of our questions has been, what is the real advantage of these snow roosts for grouse in order for them to get through the winter? So we were able to track and measure multiple grouse and individuals over time and show that their stress hormone levels, as measured here by corticosterone. And this is a naturally occurring stress hormone that we have. And in fact, many grouse and other species have. And generally speaking, when we are stressed, our corticosterone levels go up. Well, we showed that over multiple winters when there were cold snaps, that many of these grouse showed increases in their stress hormone levels. Meaning that those cold temperatures induced this stress response in these free-living grouse. But interesting component of this was that they were able to use this behavior, snow roosting, to basically buffer themselves from that temperature-induced stress response. So if we look at the corticosterone levels of the individual grouse that are able to roost in the snow, we can see here that that relationship disappears. They are no longer affected by those cold snaps, and their stress levels remained relatively stable. If we look at the population as a whole, what we can see is that once there’s about 20 centimeters or about seven to eight inches of snow on the ground, that the population generally of grouse experience reduced stress levels.

When you don’t have 20 centimeters on the ground, those stress levels go up pretty significantly. An interesting aspect of this is that 20 centimeters of snow on the ground is roughly the average amount of snow that Wisconsin experiences throughout the winter, but almost all projections agree that that level is gonna be decreased by half. So about 10 centimeters of snow will now be the average. And you can imagine what that’ll do for many of these grouse. So here was a nice example of snow serving as this very important refugia for grouse, but I would also point out that it’s not just grouse that take advantage of this snow refugia. We have many small mammals and plant populations and species, as well as even in fact, amphibians and frogs that go through a whole body freezing event and have to survive underneath the snow. All these species use that blanket of snow to protect themselves what is an increasingly variable winter climate. Unfortunately, almost all projections are in agreement that what we’ve seen in terms of the reduction in snow cover and the shortening of our winter season is only going to increase over time. So that was an example of behavior, and how a very important behavior in terms of snow roosting for a bird has allowed them to deal and cope with what is an increasingly variable winter environment. The next question is about range changes.

How might birds be changing in terms of their distributions over time and over space in relationship to climate change? So back in the 1990s, when scientists first started becoming concerned about the effect of climate change on wildlife and birds, one of the initial predictions was that if we are experiencing northern or warmings throughout the northern hemisphere, that species are going to move northward in response to that. So how this would work would be that if, for example, we’ve got two species here throughout the northern hemisphere in the United States, and we’ve got that sort of orange, warm-adapted species that has its southerly distribution. And maybe we have a cold-adapted species up there in the blue, in the north. And if we’re looking at their range boundaries, what we’d expect to see for that warm, southerly-adapted species is that if warming continues, we’d see expansion, a northward movement of that range boundary as they colonize new areas. If you’re a cold-adapted species, however, what you expect to see is a retraction in that southerly range boundary, and a movement northward. Taken together then, what we would expect to see from many species is what’s referred to as a poleward shift in their ranges over time. But how can we go about measuring that from multiple species, multiple regions of the world? Well, one of the tools that we have at our disposal are breeding bird atlases. Breeding bird atlases are a citizen science effort where volunteers go out and they record the presence or absence of multiple birds is in what’s referred to as these atlas blocks. So what you can imagine, it’s almost like an ice cube tray that’s spread out across a state, or in some cases an entire country, and volunteers are going out and recording what birds that they’re seeing in different types of habitats within each of those different blocks. Here in Wisconsin, we have well over 5,000 atlas blocks and over 1,000 different volunteers go out there and they record what bird that they have seen over roughly about a five-year period.

There’s 400 or so atlases, if not more, that are conducted throughout the world. And this paints a very important picture in terms of where species are found throughout a given region or state. The most powerful aspect of atlases is that you can repeat them. So here in Wisconsin, we had our first Wisconsin breeding bird atlas between 1995 and 2000, over five years of collecting data. And we just wrapped up our second atlas. So what can you do with two atlases to answer this question about range shifts? So for example, here we’ve got a beautiful bird, the evening grosbeak. It’s a northerly distributed, you could call it a cold-adapted species. And here are its distribution in the first Wisconsin breeding bird atlas. There you can see those purple and pink atlas blocks in which volunteers recorded the presence of the evening grosbeaks. And perhaps we could kind of delineate their range boundary there, in terms of their most southerly distributed location in the state.

So what happened when they went back out there for the second atlas? Now, that’s the map in the second atlas. And we can see that the number and the presence of evening grosbeaks declined significantly over time. So much so that we might imagine that their range boundary has shifted northward. What about a warm or southerly-adapted species? So here’s the orchard oriole. Again, another beautiful bird that’s generally primarily associated with more southerly areas of this country. And all those dots you can see there are where they recorded them in the first Wisconsin breeding bird atlas. And maybe again, we can delineate where that range boundary is. What happened 20 years later? A massive increase in their distribution and range, and a strong push in that range boundary over time. This type of phenomenon, a poleward shift, has now been documented in multiple states and regions throughout the world. It’s not just been documented for birds, but also for mammals, as well as insects and plants.

So much so that we’ve estimated that many of these birds have shown a systematic poleward shift of roughly about 10. 5 miles per decade. So over 30 to 40 years, we’re talking about bird ranges that are shifting 30 to 40 miles. The question then is that if all these individual species are moving, what are we seeing in terms of entire communities of birds? So to answer this question, I’d say it’s always fun to think about how backyard birds are changing over time. Again, to explore this, we need to turn to citizen science. And one of the programs that I’ve been particularly interested in has been data from Project FeederWatch. Project FeederWatch is a citizen science program that’s run by the Cornell Lab of Ornithology and Bird Studies Canada. It enlists well over 20,000 people every year to go out and watch the birds in their backyards. And so, with this map, you can see that each one of those little blue dots actually represents a Project FeederWatch participant. So when people outside and looking through their kitchen window at their backyard bird feeders, they’re recording the number of birds that they see showing up and the species, every two days across a five-day period throughout the course of the winter season.

When you have this kind of data, you can start analyzing the composition and community of birds in your backyard. So Project FeederWatch has been conducted since 1990. And we were really interested in whether or not the composition and the community of birds are changing in relationship to climate change. So if you can imagine that you’re a Project FeederWatch participant, and you’re looking at your backyard bird feeder, you might see an assemblage of birds that look a little bit like this: with Northern cardinals and tufted titmouse, and goldfinches and blue jays. When you live in the Mid-Atlantic states, maybe you have seen many of these same species and the usual suspects, but maybe you start seeing some other species as well. Maybe juncos, as well as house finches and black-capped chickadees. And as you move more north, let’s say here in the Great Lakes, well, now we have another assemblage and community of wintering birds. Maybe you see American tree sparrows and white-breasted nuthatch. So if all these different species are potentially moving and changing their ranges in relationship to a shifting climate, then are we actually beginning to see an entire change in the community of birds? And that’s exactly what we’ve seen since 1990. So over the last 20 to 30 years, we’ve seen that many of these northerly bird communities are becoming increasingly dominated by these southerly and warm-adapted species.

So much so that we think of this as the reshuffling of the winter bird communities here in North America, where warm-adapted birds are increasing in their distribution and their numbers. Many of these are smaller-bodied species that are more sensitive to climate and can take advantage of these potentially warming winters and changing conditions, and have generally been southerly species that are increasing over time. So this has led us to believe that more than half of observed animal range boundaries have already shown a documented response to modern climate change by moving and shifting their ranges polewards over time. In terms of phenology now, range changes generally speaks about changes at geographic levels, but phenology is looking at changes over time. To borrow a quote from Aldo Leopold, who described phenology as “Many of the events of the annual cycle reoccur “year after year in a regular order. “A year-to-year record of this order is a record “of the rates at which solar energy flows to “and through living things. “They are the arteries of the land. “By tracing their response to the sun, “phenology may eventually shed some light on the ultimate enigma, the land’s inner workings. ” I think what Leopold is poetically capturing here is that the variation and changes in the Earth’s system happen in a very predictable fashion, as the reoccurring shift from winter to spring across the northern hemisphere. And so, if we are seeing warming, the question is how are these patterns changing over time? In particular, one clear behavior that we can focus on for birds is migration and spring migration.

So again, we can turn to Project FeederWatch data to look at this. Here, we are seeing Project FeederWatch data for American robins. Those red areas are areas with a high number of robins, those sort of yellow areas have maybe a few robins, and those gray areas have no robins. And what this captures is that overwintering range and distribution of American robins, where they’re generally overwintering in large numbers in the Southeast and the Northeast and along the coast, and are few and far between in the upper Midwest. What about February? Looks a lot like January. Generally overwintering in these areas for the most part in the early 1990s and 2000s. But in March, we see the arrival of spring and the migration phenomenon begins. A large number of these individuals of robins and other species shift northward and move northward to start looking for their breeding grounds. And what we’ve been able to document using citizen science data like Project FeederWatch is that the spring arrival for many of these short-distance migrants are moving earlier and earlier, so that their first arrival in the 1990s may have been somewhere maybe in mid-March, and now is happening in the 2000s much more like late February or early March. And the species that are really taking advantage of this are species like brown-headed cowbirds and robins and red-winged blackbirds.

And these are all species that tend to overwinter in the southern part of the United States. And these are the ones that are showing some of the fastest rates of changes in their spring arrival and migration. But then the question is, are we seeing changes in their breeding as well? Are they beginning nest building and egg laying earlier and earlier? And that’s exactly what we’ve been able to document as well. One program that has been fascinating to explore has been data from the nest record programs. And again, these are citizen science data, volunteers going out, finding nests, and writing down and recording what species are nesting and how many eggs they’re finding and whether or not that nest was successful. Some of these nest record programs go back to the 1960s. And what we’ve been able to document is not only are birds arriving earlier at their breeding grounds, but they’re also beginning to nest earlier. And this is definitely true during very warm springs. However, we are entering a new era of citizen science and data for birds throughout the world. And one program that we’re particularly excited about is eBird.

eBird is another program that’s run through the Cornell Lab of Ornithology, which people record what birds that they are seeing in real time throughout the world, and continuously contribute that data to an online database. That biological database is one of the fastest-growing databases in the world. When you have data now, and observations that people are collecting in real time, we can begin to explore how species are shifting in terms of their migration and their distributions. Here, we have a statistical model that shows where tree swallows are likely to occur at different parts of their annual life cycle. So here we can see their migration in November, December, where they’re overwintering in central and southeastern United States, and then moving northward and arriving in spring and summer to their breeding grounds. An amazing power and representation of citizen science, and being able to explore how those migration patterns are changing. One real powerful way of doing this is to combine these observations with satellite data, and measurements of what’s referred to as the Green Wave, which is changes in productivity and springtime emergence of plants in the northern hemisphere at the end of winter, into spring, and fall senescence. And by combining these two different data sources, we can show how birds ride that greening up, that changing of the ecosystem from winter to spring to summer and fall. What we’ve shown is that many of these birds are in fact taking advantage of an earlier and earlier Green Wave. So much so that they’re arriving about 2.

5 days earlier per decade. The birds that can really take advantage of this are birds that tend to be a little bit slower in their migration. They kind of come a little bit earlier in terms of that migration period in March and April, and they’re the ones who have to travel the least amount, because they’re overwintering here in the United States. They’re not going all the way down to Central and South America for their wintering grounds. However, what we’ve been able to show is that that change in phenology is not consistent across different trophic levels. Meaning that the earlier phenology in plants has to be matched pretty closely by insect emergence like caterpillars. Both those groups, plants and insects, tend to respond pretty quickly to changes in spring temperatures. Some of these birds can respond to those changes as well, just like the ones I talked about, those early arriving species. But the species that have to travel long distances that we refer to as Neotropical migrants. These are species that are considered long-distance migrants that overwinter in Central and South America.

And their migratory cues are less about temperature and much more about day lengths. So when the days start shortening and changing, their migration will shift. When they start changing again in spring, that’s their cue head out of their overwintering grounds and head north. This leads to a particular problem that we refer to as phenological mismatch. So the idea here is that for a species like, in this case, the pied flycatcher, which has to migrate a very long distance; it’s a species that generally breeds in northern Europe and overwinters in North Africa. So in this case, their migratory cue is less about temperature and much more about day lengths. As we all know, day lengths is not changing over time, but temperature is, and in particular, their resources are. So for example, caterpillars are very responsive to temperature change. And this is a bird that relies heavily on those caterpillars and really timing their migration to sync up with the peak in that food resource. So when that change in food availability shifts to an earlier date, like we can see here, but their arrival date of the birds remain unchanged, you have a potential problem.

A good analogy would be if you’re lucky enough to come home for dinner at the same time, at 6 o’clock, let’s say, but every year, your dinner starts becoming earlier and earlier at the dinner table, maybe five minutes and ten minutes, but you are coming home at the same time at 6 o’clock. Well, you can imagine then, then you’re sitting down eventually for a cold dinner. And that’s exactly what’s happening with these birds, that their resource and their food availability is moving earlier, but their arrival time is unchanged. Now, for adult birds, that’s actually not that bad, not that big a deal. They can take advantage of different resources, but in particular, what that food availability is good for, and that peak in food availability is that they have enough food available to feed to their nestlings. And so what we’ve found over time is that this phenological mismatch is most acute for these long-distance migrants that are really chasing that peak in caterpillar abundance, in particular so that they can feed them to their young. Their arrival time is unchanged, how long it takes to find a mate and set up a territory, build a nest and start laying eggs. That all has remained the same, but it’s no longer synchronized with that peak food supply. In particular, those species that have to travel the longest tend to be the most desynchronized with their food. And in those populations, we’re seeing in some cases, a 90% decline over the past two to three decades.

So we’ve gone through an example of behavior, of range changes, and changes in time, changes in phenology. Well, what about population declines? To explore this idea that climate change could in fact be leading to population declines, or at least contributing to them, I’m gonna focus on a group of birds that we know are in trouble, and these are grassland birds. So I think many of us in the Midwest are familiar that many species will occupy these prairie grassland, in some cases agricultural lands, species like bobolinks, eastern meadowlarks, Henslow’s sparrows, and dickcissels. What we know is that many of these populations of these species are declining significantly, as seen here. All those red areas that we see throughout the maps of North America for these three species of grassland birds are areas where we’re seeing declining populations. What is causing these declines? Well, we know that grassland habitat is one of the most endangered type of habitat and ecosystem in North America. We’ve lost well over 95% of native prairies and grasslands, primarily due to agricultural intensification and the conversion of native grassland to agriculture, as well as a rise and spread of suburban and exurban developments. So habitat loss is absolutely the primary threat affecting populations of grassland birds, but unfortunately, another threat is climate change. So you can imagine these grassland systems are highly exposed to changes in temperature and precipitation. So much so that when there are extreme events, many of these grassland birds are highly exposed to these flooding, as well as drought events that can occur over decades.

We’ve estimated that well over half of grassland birds are already facing additional pressures of climate change, as well as habitat loss. And that these grasslands are becoming drier and more exposed to extreme events. And even some of the common species that we consider to be common are species of concern. In particular, these climate pressures are interacting with habitat loss. So when we’ve explored how nest success, so the ability of birds to raise nests successfully in relationship to temperature, what we found is that these smaller patches, these more fragmented grasslands, are exposed to these extreme temperatures. And that’s really where we’re seeing the decline in nest success. So these grassland birds are being increasingly pushed to these smaller and suboptimal grasslands. While at the same time, they’re experiencing extreme temperature changes both in spring and summer, and these concurrent effects on their ability to reproduce. What this has amounted to is that we’ve seen the loss of roughly 720 million grassland birds since 1970. In fact, if we look at all the different growths of birds species from forest species to wetland birds, grassland birds are showing the biggest declines.

A 53% population loss in grassland birds since that 1970 period. And even species that we once thought of being relatively common like eastern meadowlarks here, we’ve lost three out of four meadowlarks during that time period. And lastly, following behavior and range changes and shifts in phenology, as well as population declines attributed to climate change, the other big and important component is disease and the emergence of disease outbreaks. One eye-popping and very visual phenomenon is when we have mass mortality events in the Great Lakes. And we can see this over time where we’ve been able to document that in some years, we get a large number of bird carcasses coming up on shores. So here’s Lake Michigan, dating back to the 1960s. And you can see in some years, thousands of bird carcasses wash up. And then the other important pattern is that you can see that the prevalence of those outbreaks and those big mass mortality events is becoming more common in the 2000s. And it’s just not Lake Michigan. We’ve seen it in other Great Lake systems as well, like Erie and Ontario.

So what is happening here? These type of outbreaks are largely considered to be botulism outbreaks. Botulism outbreaks start with the prevalence of an anaerobic bacterium, a bacterium that grows in these low-oxygen environments, that leads to these botulism type E outbreaks in all systems, in all the Great Lakes. The botulism type E produces the neurotoxin, which is ingested and is magnified in many of these bird species. It leads to a loss of motor control, third eyelid paralysis, and what’s referred to as the limberneck syndrome, where they lose muscular control in their neck and slowly, their head descends below the water surface level, they experience respiratory distress, and they drown. This all begins in the sediment and alga outbreaks that happen along the lake bottom and in the shallow or surf, shallower waters. This bacterium proliferates through the food chain, from mollusk and crustaceans, all the way up to bottom-feeding fish. And then of course, the birds that are eating the fish ingest it as well. So this to the perfect example of what’s referred to as biomagnification. And the creeping up of this bacterium through the food chain and affecting multiple species of birds that use the Great Lakes, especially during migration. Species like common loons, long-tailed ducks, horned grebes, and ring-billed gulls.

So how might climate change be exacerbating this problem? Well, we’ve used satellite data to identify those years when we see these big, massive outbreaks. And one thing that is relatively common throughout all these years is when lake temperatures rise and are warming, which is what we’ve seen historically and into the future, as well as the presence of these algae mats that have been contributing and getting worse due to the runoff from agricultural areas. When you have these two components together, warmer waters and the prevalence of algae, that’s when you get these botulism outbreaks. And what we’re beginning to see then is that these warming conditions will synchronize these outbreaks from multiple species so that when the outbreaks do occur, they affect more species and extend across larger areas of the lakes. So this returns us to this idea of birds as sentinels of climate change. And what I would say is that given these lines of evidence, our sentinels are telling us that something is in fact wrong. We’ve seen evidence of behavioral adaptations that can only help so far, significant range changes across the globe, phenological changes, but also mismatches for those species that are unable to track with a changing climate, clear evidence of altered communities, and populations are increasingly on the brink due to the synergistic and interactive effects of not just climate change, but habitat loss. And finally, the climate-induced risk of emerging infectious diseases that can affect multiple species over large areas. In terms of what we expect to see in the future, almost all projections are in agreement that even under our best estimates, by 2040, we’re gonna be about 1. 5 degrees warmer than we were compared to pre-industrial time.

That by 2060, it’s more likely to be about two degrees warmer. And by the end of the century, we’re pushing three degrees. But under the worst case scenario, that may be even worse and maybe even far-reaching and warmer temperatures. And we begin to look at this in terms of the geography and the extent of that warming. We can see that compared to the late 20th century, we’re only at the tip of the iceberg of warming. But by the end of the 21st century, we’re likely in the realm of two, four, and in some cases, maybe in these northerly environments, six degrees warmer than where we were in the pre-industrial era. In terms of changes in precipitation, what we’re expecting is that dry areas will only become drier, and wet areas will only become wetter. A lot of climate scientists are now concerned that we are getting to the point of what’s referred to as planetary tipping point. The idea here is over the last 10,000 years, we’ve benefited from a climate system that has allowed us, as a species, to dominate the world. But because of human-induced changes in the land, as well as fossil fuel emissions, we’re getting to the point where so much warming will kick in intrinsic feedback cycles and systems in the Earth’s climate system.

So much so that we will be entering a new geological epoch of a hothouse Earth, which will be characterized by warmer temperatures, mega droughts, increased extremes like flooding and earlier springs, as well as the persistent and chronic loss of snow cover around much of the northern hemisphere. But we really haven’t reached that point yet. We do have changes that can be enacted that can put us on a different course in terms of Earth system stewardship, and what we can do in terms of stabilizing the Earth’s climate system. When we start thinking about the future for these species, we are beginning to get a sense that many of these species will be exposed to an increasingly novel climate space. For example, the Audubon Society has put a lot of effort in terms of trying to predict which species are going to be most affected by our future climate space. Here, you have the common loon, showing their wintering range climate, as well as their breeding range climate in the year 2000, 2020, 2050, and 2080. And what we can see very clearly is that that climate space, both in terms of where they overwinter and where they breed is shifting strongly, strongly northward. So much so that here in Wisconsin, that climate space where they’re breeding will be completely gone by the middle of the century. They’ve estimated that over 300 bird species will lose more than half their climate space by the end of the century. So let’s go back to my original idea, my hypothesis: Birds are awesome.

But the question is, are we pushing them to the limits of their awesomeness? Indeed, our sentinels are telling us that something is wrong in the mine cave, but unfortunately, we can’t really evacuate the mine. So I’ll make a couple of final points when we think about climate change adaptation. One is that degrees matter. So here we see a chart looking at the proportion of birds that are losing more than 50% of their range by the end of the century under different scenarios of global warming. So 1. 5, 2 degrees, 3. 2, and 4. 5 degrees. What I would point out is that when warming is limited to 1. 5 degrees compared to with 3 degrees, the number of species projected to lose more than half their range is reduced by almost 40%.

Meaning that if we constrain our warming to 1. 5 degrees, we might be worrying about roughly about 10%, 12% of these birds. As opposed to warming of three degrees or more, where now we’re talking about more than half of these species are going to be increasingly at risk ’cause they’re losing much of their climate space. The other aspect of this is oftentimes noted that birds and other species will simply adapt. That birds, mammals, plants have all experienced pretty amazing changes in the Earth’s climate system, from glaciation to deglaciation events. And so, birds will simply put on that gas mask, so to speak, and be able to kind of survive those changes and what they’re experiencing now. There’s a couple reasons why this is likely not going to happen. One is that the rate of warming that we are experiencing now and are predicted to experience over the next 50 years is unprecedented. And because of that, the rate of adaptation is likely not going to match that rate of warming. Another important point here is that we have altered the Earth’s template.

We’ve converted more than 40% of the Earth’s surface to agriculture. So all those corridors and pathways that used to exist for species to be able to move in response to a changing climate are no longer there. Finally, I’d like us to think about this idea of climate-smart conservation for birds. And I think many of these ideas and strategies are not novel or new to us. We can think about identifying refugia. How do we manage their habitats? How do we think maybe about translocating species that are particularly vulnerable? For those species that are actively hunted and managed, maybe we should revisit some of those harvest quotas, think about additional monitoring of those populations. Perhaps we need to revisit protected lands, like sanctuaries or wildlife management areas or national parks. Are these areas still going to serve the same purpose that they do now, 50 or 100 years into the future? And finally, we need to better monitor and manage disease outbreaks when they occur, and to anticipate how climate may be influencing those disease risks. So it leads us to this question of “What can I do?” And I would say there’s a couple things. That first, we can continue to thrive for being more energy efficient in our own household and lifestyles, whether it’s changing to an electric vehicle or thinking about energy efficient appliances.

I think every little difference we make does add up. Second, environmental issues like climate change oftentimes rank high on national polls and suggest that people are concerned about this, but sometimes they don’t enter the political discussion. And I would encourage us to think about climate change not just globally, but also locally, making it an issue for local politics as well. What can we do at the county level, at the city level, and at the town level? And finally, let’s continue to tell stories. This may not necessarily be in terms of climate change, but just continue to talk to your friends and partners and family about some of the changes that you’re seeing, maybe in your own backyard. Are there species that maybe you saw when you were a kid that you no longer see? Are there species that you don’t remember seeing that are suddenly showing up? I think these stories are important and help to convey a broader message about how species and birds are responding to climate change. And finally, become a citizen scientist. Join iNaturalist, eBird, or Project FeederWatch. You don’t have to be an expert, you can be a beginner, but every single data is important in terms of what we can say in terms of how birds are responding to climate change. I think it’s fair to say that I’d have a lot less to say in terms of my presentation today without those data and those efforts.

And with that, I’d like to acknowledge what is probably one of the most inspirational component of what I do, which is working with a whole host of graduate students and research scientists, as well as collaborators and funding agencies who see the value of this work and will continue to work and research into the future. So thank you for joining me today. I hope you can start seeing how birds are these important sentinels of climate change, and as a call to action of what we need to do in order to mitigate and adapt to a changing climate. Thank you.