Balancing site fidelity and exploration: individual movement strategies of migratory geese under extreme drought

Abstract

Animal migration is an adaptive strategy for exploiting spatio-temporal fluctuations in resource availability, where site fidelity provides advantages under predictable conditions. However, under global climate change and habitat degradation, it remains unclear how waterbirds adjust trade-offs between spatial memory and habitat exploration in response to environmental fluctuations. Poyang Lake, the most important wintering site in the East Asian–Australasian Flyway, is facing an increasing frequency of extreme drought events, offering a natural experiment to investigate these behavioral adjustments. This study integrated high-resolution GPS tracking data (2018–2025) from 27 Tundra Bean Geese ( Anser serrirostris serrirostris ), including 16 individuals tracked for ≥ 4 years, with hydrological dynamics. We classified sequential trajectories based on the relationships between current and historical utilization distributions, defining six spatio-temporal categories. A dual-track analytical approach was implemented: the first evaluated responses of population and individual home range shifts to water levels, while the second identified stable behavioral strategies via dimension-reduction clustering. Finally, linear mixed-effects models revealed strategy-specific responses to drought. At the population level, home range area expanded significantly as water levels declined ( \(\beta=-1071.62,P=0.005\) ); individual responses varied. Three distinct movement strategies were identified: (1) Faithful, maintaining high site fidelity via Persistent Core (47.2%) and Proximal Exploration (25.1%), driving population-level compensatory expansion; (2) Exploratory, showing low fidelity and relying heavily on Novel Colonization (73.5%), with home range area decoupled from water level fluctuations; and (3) Balanced, exhibiting moderate site fidelity and highest use of Historical Reoccupation (19.5%) among strategies, significantly contracting home ranges under drought in opposition to the population trend. The population-level compensatory expansion masks individual behavioral heterogeneity. This study reveals divergent movement strategies in Tundra Bean Geese under extreme drought at Poyang Lake. Intraspecific behavioral diversity and phenotypic individuality drive distinct patterns of site fidelity, dictating divergent trade-offs between spatial memory and environmental stress. The proposed spatio-temporal framework offers a generalizable tool for decoding animal spatial decisions under climate change.