Is climate change making our birds extinct?

Analysis: new research finds that birds may fail to adapt fast enough to climate change thus increasing the odds of local extinction

Around the turn of the 21st century, frog species started to disappear mysteriously from cloud forests across Central and South America. The immediate finger was pointed towards a spreading fungal skin disease, but closer inspection revealed that warming local temperatures were making life easier for the fungus, spelling trouble for the frogs. As the lead researcher of the study, Alan Pounds, put it at the time, "disease is the bullet killing frogs, but climate change is pulling the trigger".

The frog study exemplifies the so-called attribution problem in climate change research: if a species goes extinct at the same time as climate is changing, can we pin the former on the latter? If an extreme heat wave occurs, can we attribute the event itself to climate change?

The problem is that many co-occurring phenomena could be the reason behind a given event and pure chance also comes in. We cannot easily (or ethically!) do experiments where we manipulate just the climate while keeping everything else constant, and then see what happens.

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From RTÉ Lyric FM's Naturefile, Anja Murray looks into the world of the frog

But one thing we can say for sure is that climate change is loading the dice, such that extreme heatwaves and species extinctions are becoming much more probable. If an athlete takes steroids and wins a race, did the steroids make them win it? We can never say for sure, as the athlete may have simply been in good form on the day, but clearly athletes on steroids will tend to win more races than clean athletes, all else being equal.

Which brings us to the birds. In a new study led by the ecologist Viktoriia Radchuk, which brought together a large team of international collaborators (myself included), data were collated from scores of long-term population studies of many different animal species, the majority of which were birds. The goal was to test for general patterns in how species are adapting to climate change, and four main findings emerged.

Firstly, animal species in temperate regions of the world are on average advancing their phenology, i.e. the timing of important life cycle events like breeding and migration, as their environments warm up. Secondly, these responses are a good thing in that they allow populations to partially track changing seasonal patterns wrought by global warming. For example, breeding earlier when temperatures rise can allow birds to remain in synchrony with an advancing seasonal peak in food supply (e.g. insects that are abundant for only a short window in summer). However, these behavioural adjustments are not always perfect and the birds may shift at a slower rate than their prey, limiting the number of young that can be successfully raised each year.

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Indeed, our third result was that, on average, these populations are experiencing natural selection to breed or migrate earlier. This is essentially a Darwinian process, whereby the early bird not only catches the worm, but also produces more chicks who in turn survive better. If breeding time has a genetic basis, then early birds pass on their genes for early-breeding at a faster rate than late birds pass on their late-breeding genes. The population as a whole thereby undergoes adaptation.

This then led to an obvious question: can these populations adapt fast enough to cope with future climate change? This question, of course, can only be addressed by some sort of modelling, just as meteorologists cannot tell you with 100% certainty whether it will rain tomorrow. Rather, they give you a forecast – essentially an educated guess, backed up with tried-and-tested mathematical models of how weather works.

In our case, we used an evolutionary model that compared the observed climate change response of the population in question against a gold standard, "theoretically perfect response". Although it can sometimes proceed rapidly, Darwinian evolution is not without limits, especially if the climate changes too rapidly.

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This led to our fourth and final finding. Across the 13 species for which we had sufficient data, the model forecasted that future changes in phenology will likely not be enough for these populations to cope with future warming. In other words, they may fail to adapt fast enough to the accelerating climate change that is coming down the tracks, increasing the odds of local extinction.

Technically, the term extinction means that the whole species dies out everywhere it was formerly found. Our study was focussed on single study populations in given places, e.g. a woodland where the local Great Tits or Blue Tits are monitored in nest-boxes provided by the researchers. As species, however, Great Tits and Blue Tits are found across most of Europe and into Asia and North Africa; thus the loss of local populations does not mean the loss of the entire species.

If populations cannot adapt to changing climate in their current locations, the species as a whole may still be able to avoid global extinction through a process known as "range shifting". The range refers to the total geographic area where a given species is found, and the shifting part means that the range itself moves, as some populations slowly fade out (e.g. in the hottest regions) and new populations are established elsewhere where the climate is more suitable (e.g. at cooler latitudes or altitudes).

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Of course, if everywhere warms up rapidly, and this continues unabated, the species may be unable to move quickly enough to stay in the game, or it could run out of suitable places or be geographically trapped by barriers to dispersal (e.g. species found only on remote islands or mountaintops). And here is where the major concern arises: our planet as a whole is currently warming faster than at any time in the past 10,000 years, and some climate models are predicting that warming over the coming century may be 10 times faster than anything seen since the time the dinosaurs went extinct, some 65 million years ago.

A particularly important study in 2004 examined potential future range shifts in over 1,000 species of plants and animals and reached a rather stark conclusion. It found that 15 to 37% of species (across the regions and taxa examined) will be "committed to extinction" by 2050 under a mid-range climate warming scenario. The study did not account for local populations potentially adapting their behaviours and traits in their current locations, but it nonetheless served as an important warning of what could happen if warming continues unabated.

By contrast, our model-based forecasts focussed purely on adaptive changes occurring within a given place, so the findings are not easily scaled-up to the entire geographic range of the species. The challenge for future studies is to build better models that account for both of these aspects. In other words, we must forecast, under different climate scenarios, likely changes both in where species may be found in the future, and in the physical and behavioural characteristics of local populations, which together will influence global extinction risk in a warming world.

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What about Ireland's birds? Will climate change drive them extinct? Should the Irish climate become increasingly unsuitable for some species, then the chances are that these species will no longer be found here in the future, either as breeding birds, overwintering birds, or passage migrants. At the same time, other species from warmer parts of Europe may find the new Irish climate increasingly attractive, such that local losses are balanced to some extent by gains.

There is some evidence that such changes in our avifauna are already occurring. For example, recent declines in the numbers of wintering waterbirds in Ireland could in part reflect shifts in migratory behaviour, where warming at higher latitudes means that some species no longer have to travel all the way to Ireland to find snow/ice-free conditions. Recent new arrivals to our shores such as the Little Egret have also been speculatively linked with climate change.

Other factors may also be at play and it is not unheard of for birds to suddenly expand their ranges. For example, the ubiquitous Collared Dove first graced our shores only in 1959, as part of a rapid 20th century range expansion from Asia to Western Europe. None of our bird species are endemic to Ireland, meaning they are also found in other places in the world, although we do have a few endemic subspecies (e.g. White-throated Dipper, Coal Tit, Eurasian Jay, Red Grouse) – local flavours on a wider theme. Thus, the loss of a given species from Ireland, while tragic, may not be accompanied by the loss of that species from the whole planet, although clearly the loss of unique subspecies would be a much bigger hit.

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Just like the doping athlete about to enter a race, we cannot say for sure that species A or B will definitely go locally or globally extinct because of climate change -- no-one can, bar the odd gifted soothsayer. But we can conclude that many species will struggle to adapt or move fast enough and that the risk of population declines and species extinctions over the coming decades is therefore elevated, assuming warming trends continue.

A further sobering element of Radchuk's new study is that the 13 species for which forecasting was done are (currently) relatively common and abundant, and hence well-studied. The fear is that the prognosis could be much worse for other poorly studies species that are already currently rare or endangered. One must, however, be careful not to tar all species with the same brush – some may be more susceptible to climate change than others, and others still (including potential pest species) may even thrive in a warmer world.

Meanwhile, our wildlife faces a suite of other more immediate threats including habitat loss, pollution, unsustainable hunting or bycatch, and invasive species. One or two of these alone would be bad enough, but taken together they can push species over the edge rapidly. It is therefore vital that we push our leaders and policy makers into climate action and support organisations like Birdwatch Ireland and others that continue to do vital on-the-ground conservation work and awareness raising, to give birds and their habitats a fighting chance.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ

Is climate change making our birds extinct?

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Tom Reed