Tracking the long way around: seasonal migration strategies, detours and spatial bottlenecks in common cranes wintering in western India

The common crane Grus grus, being widely distributed, abundant, and relatively easy to monitor, with long-distance migrations across diverse and sensitive habitats, is well-suited as a sentinel species for assessing the ecological integrity of the Central Asian Flyway (CAF). While migration routes and stopover sites of the common crane in the CAF are documented, seasonal variations in migration strategies, potential detours, bottlenecks, and stopover habitat selection—important factors for flyway conservation planning—remain poorly understood. To address this, we tracked five individuals from Gujarat, western India, to breeding sites in southwestern Siberia using solar-powered GPS-GSM transmitters, enabling high-resolution, multi-season analysis of their migration strategies, routes, timing, detours, bottlenecks, and stopover habitat selection. The results highlighted seasonally differential migration strategies in common cranes. The analyses confirmed significant seasonal differences: spring migration covered greater distances, lasted longer, and was slower, with a longer stopover duration and reduced straightness. The observed migration routes deviated significantly from the simulated straight-line path, forming distinct detours likely to avoid the Hindu Kush mountains and take advantage of resource-rich areas. These detours resulted in routes that were 23.3% longer in autumn and 36.8% longer in spring compared to the shortest possible path. The tagged common cranes followed distinct seasonal migration routes that converged in Turkmenistan, creating migratory bottlenecks in southern Turkmenistan, Afghanistan, and Pakistan. At migration stopover sites, common cranes showed the highest probability of habitat use in bare ground (0.18) and cropland (0.13), suggesting a preference for open landscapes by the species. Our findings reveal the adaptive strategies of common cranes in response to seasonal and topographical challenges. Cranes undertake substantial detours, potentially to optimize energy expenditure and access favorable stopover habitats. The identification of migratory bottlenecks in Turkmenistan, Afghanistan, and Pakistan highlights the region's critical importance for conservation efforts for migratory birds.