There is a group of cats that lives around my house, and over the years I have observed something that has always fascinated me. Although each of them possesses certain innate behavioural traits that do not require prior experience,such as knowing what to eat, how to groom themselves, when to show aggression, or how to interact with other cats—they are all remarkably different from one another.

Despite growing up in the same environment and experiencing similar conditions from birth, each individual develops a distinct personality. Some are incredibly shy and cautious, while others are bold, curious, and friendly. This variation has intrigued me for a long time. I often find myself wondering why these differences exist. What shapes an individual's personality? Is it purely genetic, or do subtle experiences influence who they become?

These personality differences also seem to affect their ability to survive. A bold individual is more likely to take risks and may be rewarded by catching prey or discovering new food resources. In contrast, a shy individual may avoid those risks and consequently lose such opportunities. Observing these cats made me wonder: if such behavioural variation exists among domestic cats living in a relatively safe environment with limited ecological pressures, what happens in the wild? How do these individual differences influence survival when animals face real competition from both conspecifics and heterospecifics? How do personality, cognition, and behaviour shape their ability to adapt to changing environments?

In search of answers to these questions, I began exploring the scientific literature. That is when I came across the paper by Mettke-Hofmann (2017), "Avian Movements in a Modern World: Cognitive Challenges."

I was immediately captivated by the paper because it explores the cognitive abilities of animals, specifically migratory birds, a group I have always been particularly fascinated by, and compares them with resident and partially migratory species. It offered a fascinating perspective on how migration itself may shape cognition and behaviour.

Some of my key takeaways from this remarkable paper were:

• Migratory birds possess a relatively larger hippocampus, containing more neurons, which enhances their spatial memory. However, they tend to have a smaller overall brain size, possibly as an adaptation to reduce head size and improve aerodynamics during long migratory journeys.

• Migrants exhibit superior spatial memory compared to resident species. This enables them to remember profitable feeding sites and successfully return to these locations during subsequent migrations.

• Migratory birds are generally less exploratory than resident birds. When introduced to a novel environment, they tend to explore cautiously and to a much lesser extent than resident species.

• Rather than relying solely on personal exploration, migrants often use social information, joining flocks already exploiting an area or observing the behaviour of resident birds before selecting suitable foraging or stopover sites.

• Because migrants frequently return to previously used sites, they can be more vulnerable to environmental changes. Anthropogenic disturbances or habitat alteration at familiar sites may cause them to abandon these areas or fail to return altogether.

• Individual behavioural differences also exist within migratory populations. Some individuals are bolder and more willing to take risks, whereas others are more cautious. Interestingly, birds that migrate earlier often experience higher reproductive success and improved survival compared to late migrants.

Overall, the paper suggests that migratory birds have evolved exceptional spatial memory that allows them to repeatedly locate important habitats. However, this reliance on familiar sites, combined with a lower tendency to explore unfamiliar environments, may make them particularly vulnerable in a rapidly changing world. At the same time, the presence of behavioural variation among individuals, where some are more exploratory and risk-taking than others—and their ability to use social cues may help certain individuals discover and colonize alternative habitats when traditional ones become unsuitable. This interplay between cognition, personality, and environmental change may ultimately influence population persistence and explain why some migratory species are more vulnerable to decline than others.