When experience breeds variability: age-dependent movement diversity in a successful shorebird.

Migratory species are vulnerable to habitat loss, especially migratory birds that rely on multiple stopover sites during migration. According to conventional understanding, migratory birds typically show reduced behavioral variability as they age, with their migration routes becoming increasingly fixed through experience, which may make them even more vulnerable to habitat loss along their flyway. Indeed, in the East Asian-Australasian Flyway (EAAF), most waterbird populations have rapidly declined due to habitat loss and land use changes. However, some migratory species like the Pied Avocet Recurvirostra avosetta have maintained or even increased their populations. We investigated whether this success might be linked to age-related patterns in migration behavior. Using satellite tracking technology, we monitored the movement behaviors of 48 adult and 20 juvenile Pied Avocets in eastern China from 2021 to 2024. Contrary to expectations, adults exhibited greater movement variability than juveniles. In the first two years of life, Pied Avocets performed relatively limited movements, adopting conservative migration strategies, which may reduce mortality risks. In contrast, experienced adults showed greater variability in their movement patterns. Some migrated to more southerly wintering grounds or more northerly breeding sites, and occasionally pioneered entirely new flight paths. Compared to juveniles, adult birds also showed larger home ranges during the pre-migration period and greater within-season movements during the non-migration period. This age-related increase in ranging behavior and movement variability may contribute to their population resilience in rapidly changing environments. Our findings suggest that the combination of risk-averse strategies in young birds and diverse movement strategies within adult populations, ranging from conservative to exploratory individuals, might represent an important adaptation mechanism for long-lived species facing environmental change.