When survival depends on brains: lessons from the Western Jackdaw

The growing concern about the impact of global change on biodiversity has created an urgent need to identify which organisms are most vulnerable and to understand what makes them more sensitive to extinction. Today we know that the main cause of species decline and extinction is maladaptation to the rapid and drastic environmental changes induced by human activity. Paradoxically, however, some species have actually benefited from these alterations, which has allowed them to increase in number and expand. These observations raise two key questions: why do some species cope with maladaptation better than others? And what mechanisms explain these differences?

In some cases, such as in short-lived organisms like viruses, algae or insects, the explanation lies in their high capacity to adapt evolutionarily and quickly to environmental changes. But in long-lived animals, such as many birds and mammals, evolution is too slow to “rescue” populations from maladaptation. In these situations, a plausible alternative is that their persistence depends on their brain and their ability to modify behavior in response to new environmental challenges —a theory known as the cognitive buffer hypothesis.

The COGPOP project, led by CSIC-CREAF with the participation of CTFC, the University of Antwerp, and CEAB-CSIC, explores little-known aspects of this theory by combining two complementary approaches. The first compares species to identify which cognitive traits distinguish those that better tolerate change and under what conditions they evolved. With the help of evolutionary models, we study how drastic environmental changes that occurred in the past —such as those associated with the colonization of marine environments by birds and terrestrial mammals— favored adaptive changes in brain areas involved in cognition, and how this shaped life strategies and demography.

The second approach focuses on individuals: how they make decisions and how these influence population demography and evolution. We do this through a long-term study of the Western Jackdaw (Corvus monedula), a social, long-lived, and surprisingly intelligent bird.

Since 2015, we have been studying a population of jackdaws breeding in nest boxes and nesting towers set up by the Government of Catalonia in the Lleida plain to enhance biodiversity. Each year we capture, measure, and mark chicks and adults, observe their behavior, and collect reproduction data (e.g., clutch size and number of fledglings) and survival. We also use cameras and sensors to record what happens inside the nests: who feeds, when the parents enter and leave, how they cooperate and how they compete. In addition, we conduct genetic analyses to determine sex and kinship relations among individuals, which allows us to distinguish evolutionary responses from plastic responses.

With all this information we can estimate the fitness of individuals and of the population, and assess how the population responds, demographically and evolutionarily, to environmental changes —such as rising temperatures driven by climate change. Moreover, we can understand how individual decisions —such as advancing reproduction when it gets warmer— can buffer environmental pressures, and explore how these decisions shape microevolutionary trajectories.

The project is led by Daniel Sol (CSIC-CREAF) and his lab members Alessandra Bateman, Francis Dale, Laura Noguer, and Marçal Pou-Rossell. Collaborators include Aina Garcia-Raventós (University of Antwerp), Francesc Sardà, David Giralt and Gerard Bota (CTFC), and Jolle W. Jolles (CEAB-CSIC).

One of the main field tasks of the COGPOP project is the scientific ringing of jackdaw chicks and adults. This consists of placing a metal ring on the bird’s leg, with a unique code that allows it to be identified when recaptured. Each individual also receives a plastic ring with an alphanumeric code and a microchip tag, which enable identification at a distance or through data-loggers installed in the nest.

When we capture a jackdaw, we also take the opportunity to weigh it, measure its beak and wings, and collect samples to analyze its DNA. With all this information we can understand how individuals survive and reproduce, and therefore estimate their fitness, as well as study the decisions they make, such as when and where to breed or with whom to associate for feeding.

The jackdaw population we study breeds in artificial nest boxes distributed across the Lleida plain, and there are two types:
On the one hand, solitary nest boxes, placed on wooden poles about 4 meters high, in open and quiet areas. On the other hand, large nesting towers, each with an average of 30 nest boxes. These structures function like apartment blocks for jackdaws, encouraging colonial breeding, a typical behavior of this species.

Inside, the nesting towers resemble a spaceship: green and red lights, wires, and electronic components everywhere. Each nest box has an associated Raspberry Pi microcomputer, a camera, and other sensors. Jolle Jolles and Marçal Pou-Rossell are experts in this new low-cost, do-it-yourself technology.

Raspberry Pi are microcomputers without a screen, keyboard, or mouse that can be programmed to do almost anything. In this case, Jolle and Marçal have programmed them to record images every second to monitor what happens inside the nest boxes at all times, from the beginning of the breeding season with nest construction to when the chicks fledge. Each microcomputer sends all this information to the cloud daily using a portable wifi network built into the system. Later, the huge amount of images obtained from the multiple nest boxes are processed using artificial intelligence, to detect the jackdaws appearing in each frame and automatically quantify their parental care behaviors.