Age-Specific Survival Estimation of a Eurasian Crane Population Highlights a Long-Term Decline in Juvenile Survival

The Eurasian crane (Grus grus), a symbol of conservation success in Europe, has made an impressive recovery since the 1979 Birds Directive, with current estimates reaching around 590,000 individuals. However, this transition from vulnerability to abundance brings new challenges, particularly arising from interactions with human activities (e.g., conflicts with agriculture). Understanding the future dynamics of crane populations requires knowledge of demographic parameters that are crucial for predicting population trends and informing management and conservation measures. We analysed 37 years of data (1985-2021) from 5049 juvenile-banded cranes and 172,725 resightings, providing estimates of survival rates across age classes and over time. Our findings indicate that juveniles exhibit the lowest survival rates, while sub-adults have higher survival, and adults show a decrease in their survival probability with age, as expected with the senescence process. Over the study period, juvenile survival declined by almost 30% overall, while sub-adults experienced a smaller decrease, and adults showed no change. Life expectancy at birth was 10 years, and maximum lifespan reached 25 years. We found no difference in the survival estimates of males and females. The decline in juvenile survival over the years highlights the growing challenges likely driven by habitat degradation, climate change, agricultural practices, and increasing population densities. These findings align with previous research on crane survival and underscore the importance of understanding age-specific survival dynamics in response to environmental changes. This study highlights the challenges facing Eurasian crane populations, where further declines in juvenile and immature survival rates could lead to population declines unless compensated by a stable or higher adult survival. Effective conservation strategies will require further research into reproductive success and details on age-specific mortality causes and environmental pressures, although targeted interventions can already be implemented to mitigate current impacts of habitat degradation and climate change.