As COP26 draws to a close, with little hope for a real transformation of our ways of doing things, let’s take a look at past climates and their impacts on wildlife. We are living in the Quaternary Era, which began 2.58 million years ago; a straw in the history of the Earth, but a period with a particularly tormented climate: no less than 50 climatic oscillations of varying magnitude and duration, and between 8 and 10 ice ages in the last 800 000 years alone. Many of the species we see, including the smallest birds, existed millions of years ago. I find it absolutely fascinating that they have come through all these crises, adapting to dramatically changed temperatures and landscapes.
This is what colleagues have shown in a recent study led by Vera Warmuth from the University of Munich (1). The scientists looked at the genetics of the black flycatcher, a passerine bird weighing about ten grams and smaller than my hand, which nests in forests, parks and gardens in Eurasia, feeding on insects. The research team determined the DNA mutations in different flycatcher populations from Spain to Norway. The frequency of these mutations allowed them to date the exact moment when these populations split from each other. They found that these divergences correspond closely to major climatic events, including global temperature fluctuations sometimes exceeding ten degrees.
This was the case approximately 130,000 years ago, with an abrupt period of cooling that turned European forests into tundra and damaged flycatcher populations. At the end of this episode, around 110,000 years ago, flycatchers recolonised the spaces that were once again habitable, with distinct populations in the Iberian Peninsula compared to the rest of Europe. This early differentiation of Iberian flycatchers is surprising, as it was previously thought that it only appeared after the very last ice age, some ten thousand years ago. As Jacques Blondel, a specialist in the evolution of birds at the CNRS, confirms, “today’s biodiversity is a legacy of the climatic oscillations that have punctuated the last two million years. The study by Warmuth and colleagues has the great merit of specifying the tempo and mode of this differentiation with the help of a precise example.
The flycatchers in my area are currently wintering in sub-Saharan Africa and I cannot ask them about the posturing of COP26. It is highly likely that the ongoing warming will again transform their ranges and affect their population sizes. Recent studies show that it is already disrupting their migration, forcing them to return to Europe about ten days earlier (2). In their nesting areas, they will find landscapes devastated by intensive agriculture and modern forestry, where the insects essential to their survival are becoming rare.
(1) Warmuth, Vera M., et al. (2021) “Major population splits coincide with episodes of rapid climate change in a forest-dependent bird”. Proceedings of the Royal Society B. 288.1962: 20211066.
(2) Helm, Barbara, et al. (2019) “Evolutionary response to climate change in migratory pied flycatchers”. Current Biology 29.21: 3714-3719.