There is nothing more effective for a living being than being able to anticipate events happening around it. Being able to react before something happens gives it a significant advantage over other individuals in the ecosystem. Using a resource —such as a source of energy source , whether in the form of solar radiation or food in the case of a predator—requires the organism to be prepared from both a physiological and behavioral standpoint: if I know that the chances of encountering potential prey are about to increase, I’d better be on the lookout and not let the opportunity pass me by. Similarly, knowing that my food resource will no longer be available can save me a great deal of the energy needed to search for and detect it. This also applies to the other side: if I want to avoid being eaten (or reduce the chances of this happening), it’s always best to avoid times when predators are most active.
This subject of interactions involves adaptive processes that, from an evolutionary perspective, converge into activity cycles that strike a balance between the pros and cons of being active at different times of the day. When the events that trigger the result —such as a predator’s attack or the potential hunt for prey—are not entirely predictable (one would have to get inside the other’s head to know what it is thinking), adaptations focus on improving reaction time, detection ability, and movement speed, for example, in addition to other subject behavioral aspects such as those I just mentioned. However, in nature there are many events that exhibit a marked periodicity—occurring very regularly and having significant effects on the environment in which living beings thrive. Nothing is more rhythmic than the astronomical movements of celestial bodies. So much so that we can calculate with extremely high precision when an event of this nature will occur—as in the case of the upcoming eclipses that we will be able to enjoy in the coming years in our country.
For life on our planet, there are two fundamental astronomical movements that significantly shape the characteristics of the environment: the Earth’s orbit around the Sun and its rotation on its own axis. The former is a determining factor in climatic conditions and in the amount of energy available in ecosystems throughout the year. The tilt of the Earth’s axis of rotation relative to the plane of the ecliptic determines the rhythmic succession of the seasons. Knowing whether we are heading into a period when weather conditions will typically be favorable and energy will not be in short supply is essential for deciding when to begin the reproductive season, for example. This determines the phenology of all living beings, whose life cycles are closely linked to the regular succession of the seasons. The second, the rotation on its own axis, determines a radical and extremely rapid alternation in environmental conditions: day and night.
Temperature, light available s for production, relative humidity… these are fundamental parameters that change completely over the course of a few hours. The biology of different species determines how they best utilize the 24 hours in a day. To do so, it is not only necessary to know when the sun is above the horizon and when it has set (something relatively easy to determine) but also when twilight is approaching, whether at dusk or at dawn. Organisms’ assimilation of this daily rhythm is an evolutionary adaptation that establishes the so-called circadian rhythm—the alternation of sleep and wakefulness typical of many living beings (we cannot say that all species sleep in the strict sense of the term, but they do generally experience certain periods of lethargy throughout the day). Thus, daily rhythms are an evolutionary adaptation that allows organisms to cope with an environment that provides the most appropriate environmental and biological conditions for their biology. But what about eclipses?
Although an eclipse is a predictable astronomical phenomenon, its frequency is highly sporadic from a population’s perspective. The vast majority of living beings on our planet will never witness one because, even though the Sun-Moon-Earth alignment can occur every year, locally it happens on average at intervals of hundreds of years, which greatly limits the practicality of an adaptive response. Furthermore, it is a relatively brief phenomenon, making it difficult for organisms to develop a specific response. However, the effects it has on environmental conditions are equivalent to those of dusk and dawn, so it is to be expected that organisms will undergo changes similar to those they experience daily at these times of day. It is well known that an eclipse induces atmospheric changes related to light intensity, temperature, and even wind, which in turn trigger behavioral responses in animals: diurnal birds tend to stop singing and return to their nests, nocturnal animals increase their activity, domestic animals head to their stables… Organisms detect the change in the environment and react accordingly. The return to initial conditions interrupts the change in rhythm triggered by the eclipse, and everything remains a one-time anomaly—a minor deviation from the daily rhythm of activity, a small stumble in the routine course of the day.
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David Galicia
researcher from the Biodiversity and Environment Institute and professor at the School of Science at the University of Navarra.
13.08.2026
