In the face of increasing global warming, it's important to understand how the biological community will respond. Birds, thanks to their mobility, are sensitive indicators of global change, but there's still no clear understanding of which climate and weather components provide them with the right signals. In what form are these signals made available? How do birds know what lies ahead? How do they distinguish temporary difficulties from serious risks? Surprisingly, climate change helps answer these questions by offering a global experiment: what if the entire adaptive environment is altered? Is there a ready-made answer, or is evolution needed? In what ways, to what extent, and how quick? These are fundamental questions of evolutionary ecology, unanswerable in the laboratory.
At the Yenisei Ecological Station, the first spring bird sightings were always recorded, regardless of the primary objectives of the work. Now these data have come in handy: after all, it's rare that such observations have been conducted for half a century, especially in the absence of visible anthropogenic changes to the natural environment for many hundreds of kilometers around. The summer productivity of ecosystems here, in the heart of the taiga zone, reaches tropical levels and supports a rich nesting fauna of birds, but due to the harsh winters, almost all species are migrants. They fly here from all corners of the Old World: from Britain and South Africa, Japan and Australia.
It is known that in a boreal climate, the development of any spring process - snowmelt, leaf budding, insect activity and their prey - depends on temperature. Crossing a threshold provides the initial impetus, the accumulated sum of temperatures determines the rate of development, which then proceeds independently, according to its own schedule. In this way, all spring processes are initiated sequentially, one after another, including those that determine food availability for birds. The set of parallel phenological processes forms the environmental phenology. It depends on the temperature of the previous period, although long-standing deviations are gradually "forgotten." The same is true for the future: environmental phenology predicts development, but the accuracy of the result decreases over time.
Researchers at the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (IEE RAS) developed an index of environmental phenology and compared thousands of annual deviations in dates of spring migration with deviations in environmental phenology. They found that these deviations explain migration timing better than other climate variables, particularly on the day of arrival. The proposed phenology index exhibits robust autocorrelation, allowing birds to predict food availability two weeks in advance. It provides an adequate measure of environmental changes on a daily, annual, and multi-year scale. This measure allows for an objective assessment of the extent to which shifts in migration timing compensate for climate change.
Paradoxically, compensation for climate change cannot and should not be complete. It merely adjusts the photoperiodic calendar. Day length has been and remains a reliable guide to seasonal changes. Caution prevents deviation from it: too complete compensation can lead to an early false start of migration or the omission of the breeding season.
"We've shown that environmental phenology successfully explains migration timing. This approach can be applied to other species as well. Our findings differ in many ways from previous generalizations, but they are built on a solid foundation. Here, we examined the general characteristics of bird responses to phenological fluctuations. But each species is unique, which raises new questions. What hinders the perception of climate signals? Are all species affected by global warming? What life-history characteristics determine the flexibility of the annual cycle phases? Which species adapt more successfully to warming? Our approach allows us to compare species' sensitivity to current changes, but that's another story," explained Oleg Bursky, Doctor of Biological Sciences and Leading Researcher at the Institute of Ecology and Evolution, Russian Academy of Sciences.
RAS: "Environmental phenology determines the timing of bird migration"