Of Birds, Behavior, & Climate Change
How a little European bird keeps up with climate change
Oh how good it would be, we humans think, to have simple solutions to that grand challenge we call climate change. How easy it would be, to rally the unified, international response it necessitates. In one fell swoop, we could make immense progress in securing the future of humanity on this planet in spite of its past pitfalls.
But alas, we do not live in that world.
In exploring the natural world, we see that many animals face a similarly complex problem to solve: in climate change, they face rapid change. After just two centuries — a veritable blink of an eye to the time scales most evolution occurs on — of human influence, we live in a world where global temperatures have risen an average of 1.4 degrees Fahrenheit, where the yearly minimum of Arctic sea ice has shrunk 13.3% percent per decade, where CO2 levels have reached a 650,000-year peak.
So often we forget that this ‘we’ includes more than just humans. Humans share the earth with a profusion of life, most of which we could neither name nor describe. On this spaceship we call Earth, we humans are participants in an ancient natural system, one which prospered for billions of years before us, and could conceivably do the same after our disappearance.
Thus is the reality of life, as so eloquently forewarned by Jurassic Park’s Ian Malcolm: “Life will find a way.”
But while life itself is likely to prosper for billions of years, each species exists in a precarious balance, struggling from the time of its divergence to its eventual extinction. Through even greater toil must the individual struggle, competing with others for space and resources. How does climate change play into this struggle? By inducing climate change, we are changing the environment faster than the time evolution needs to produce adaptations.
Indeed, two centuries is not nearly enough time to allow species to adapt to climate change. It’s not enough time for montane species to search out new mountaintops as warmer temperatures — and disease-carrying mosquitoes — creep uphill. It’s not enough time for coral species to cope with increasingly acidic oceans. It’s not enough time for Polar Bears to adapt to less icy environments and the different prey species they support.
It simply is not enough.
So for those species that are adapting, what sort of adaptation are we talking about? When there simply isn’t enough time for natural selection to guide adaptations, we must consider a different form of adaptation altogether: behavioral adaptation.
And here we enter one of the most fascinating interfaces of evolution and ecology, a realm where the capacity to respond to challenges in many ways is the adaptation. When new, fast moving challenges present themselves, those species that keep doing the same thing will not be able to cope. But when sudden challenges are taken on by behaviorally flexible species, their capacity to respond in many ways — or even creatively — is the greatest of advantages. To observe the environment and adapt within the course of a lifetime is to ensure a baseline preparedness for unknown challenges.
Enter Poecile palustris — the Marsh Tit — a delightful little European relative of North America’s chickadees. In pondering how species respond to climate change, Poecile palustris helps make an essential distinction. In responding to rapid environmental change, two processes can increase species’ ability to cope: microevolutionary change and individual plasticity.
Microevolutionary change is change in a species through time, where some mutations occur in a population that are advantageous. Over time, these advantageous mutations become more common, and as such, the population is said to be adapting. This is true adaptation: it occurs at the level of the population, and never within an individual’s lifetime. Why? Once an individual is conceived in a parent, its genome will never change.
Individual plasticity, on the other hand, is all about change within a lifetime. Not true adaptation, individual plasticity entails behavioral and/or physiological flexibility. In this way, when you are having a stressfully busy day, the sort where plans are constantly changing and you just have to “go with the flow,” you are being behaviorally plastic. The only difference is that you’re not doing it for survival, not matter how much it may seem like it.
Like many other members of the family Paridae, Marsh Tits stay in the same place throughout the year, making the same individuals easy to find within and between years. All that’s needed, then, to draw conclusions about individual plasticity, is long-term tracking and a changing environment.
Luckily, the latter is inescapable, and the former can be found in Poland’s Białowieża National Park, where long-term studies have been conducted on Marsh Tits for more than 40 years.
Why, in the age of climate change, does individual plasticity matter? First, to do effective conservation on declining species, it is necessary to know whether they cope with environmental change through microevolutionary change or through individual plasticity. In other words, does ‘adaptation’ (a term used liberally here) occur between generations, or within the individual’s lifetime? Second, it is of paramount importance to know the limits of individual plasticity. Inherently, a behaviorally flexible species will be able to cope faster with climate change. Why? Individuals can each cope within the timescale of their own lives, rather than change happening only between the generations. But even the flexibility has limits, with some species — and some individuals — being intrinsically more plastic than others.
In short, it is essential to know whether individual plasticity is the solution used by a given species, and if it is, it is then essential to know that plasticity’s limit. Why? That limit is the tipping point, beyond which that species cannot cope with faster environmental change.
So how do Marsh Tits cope with environmental change? This is exactly the question Tomasz Wesołowski et al. set out to answer with a paper published this past July in the Journal of Avian Biology.
To understand behavioral flexibility, ornithologists often look at a bird’s annual schedule, or phenology, to see how it changes the timing of major life events like, say, breeding. Because breeding costs so much time and energy, and is responsible for everything on which natural selection acts, birds must time it perfectly. They must only start the breeding season when the weather is palatable, when there is enough food of the right kinds, when enough nest locations are available, and when predators aren’t too prevalent. Because there is so much pressure to optimize this timing, there are few better life events to study for solutions to environmental change.
Between 2013 and 2014, the spring weather conditions in Białowieża National Park ranged across the gamut. In late March in 2013, temperatures remained cold at -5.1 degrees C (22.8 degrees F), whereas at the same time in 2014, temperatures warmed up to 7.1 degrees C (44.78 degrees F). We have our species, and we have our environmental change.
With unforeseen flexibility, the Marsh Tits shifted the start of their breeding season (egg-laying) by up to 23 days, all in an attempt to strike the perfect balance of weather and resources. While many species — especially migratory species — have a rigid annual schedule, Marsh Tits had the individual plasticity to shift the onset of their breeding season by almost a month. Above all else, Marsh Tits are remarkably plastic. Between 2013 and 2014, the sixteen tracked individuals made these drastic shifts as a response to the environmental challenges they faced. And because it was within the course of their lifetimes, it can be extrapolated that Marsh Tits in general rely more on individual plasticity to cope with environmental challenges than they do on microevolutionary change.
Even more remarkable is that the sixteen Marsh Tits in this one location shifted their breeding start date as much as had ever been recorded throughout the species’ entire latitudinal range. This means that if one were to compare egg-laying dates between a Marsh Tit in Sweden to a Marsh Tit in Italy, the variation would be about the same: a median difference of 20 days.
If individual Marsh Tits in one location are as flexible as the entire species, then they seem remarkably well-prepared for rapid climate change. When individuals of a species are relatively “set in their ways” in regards to when they breed, it could take thousands or even millions of years for evolution to adapt them to a changed environment. Not so with Marsh Tits. Because they are so flexible, individuals of this species could make the same amount of change within a lifetime. And that, with all our grim projections, is a powerful advantage indeed.
So far, it appears that Białowieża National Park’s radical temperature shift between 2013 and ‘14 are not due to climate change. Even if they were, Marsh Tits would be ready. This advantage of flexibility, the authors say, would “suffice to adjust birds breeding times to the forecasted climate changes.”
So what we have here is a remarkably flexible species in regards to egg-laying date. Even more importantly, we have found an example of where life has found a way, where organisms have escaped the bounds of evolutionary time to cope with faster environmental challenges.
While these findings make us optimistic about the prospects of Marsh Tits in the face of climate change, we must remember that not all species are sedentary, arboreal songbirds. Across the myriad of organisms on our planet, we have equally diverse levels of plasticity in coping with change. In some species, time between generations is so short that there is no point in plasticity, as microevolutionary change is enough to keep up with environmental change. In others, time between generations is so great that plasticity is the only way individuals could cope with seasonal, annual, or even decadal environmental change.
But at least in the animal world, it appears that most species are not quite plastic enough to keep up with climate change. Most species — including birds — appear not to be flexible enough to adapt to rapid, human-induced change. Tropical species, for example, who haven’t evolved under inherently variable, seasonal conditions, are among the most limited in capacity to change with the environment.
Even more frightening is how few species’ individual plasticity have been studied. How could we possibly understand how climate change will affect a given species if we don’t know how quickly it can adapt? Even if we did know that species’ plasticity, we aren’t even close to understanding just what that plasticity means. In the case of Marsh Tit, “How do Marsh Tits know the right time to lay eggs?”, “What physiological processes allow this flexible timing?”, “What is the genetic component to this individual plasticity?”, and “How is individual plasticity maintained at the population level?” are questions to which there are no answers…yet.
We do have one answer: Marsh Tits are remarkably flexible. A single female can bide her sweet time until the right time comes to lay eggs, not to mention her uncanny ability to recognize this ‘right time’. But the mechanisms behind this flexibility? We have no idea.
When we look in nature, we do find unique solutions to that grand challenge we call climate change. But what we’ve found so far is only the beginning; while we know that some species can adapt, we know not how. Though we know some species can’t adapt, we know not why. To understand the reality of how climate change affects this little planet of ours, these kinds of questions need answers.
Perhaps somewhere in coming to understand how other species cope with climate change, we’ll find some solutions for our own species. With a deeper understanding of nature’s workings, we can better understand how to balance our species with that myriad of others.
After all, what better place to learn lessons of self-betterment than from that inexorable march of adaptation from whence we came?
Citation:
Wesołowski, T., Cholewa, M., Hebda, G., Maziarz, M., & Rowiński, P. (2015). Immense plasticity of timing of breeding in a sedentary forest passerine, Poecile palustris. Journal of Avian Biology. Retrieved October 22, 2015.
