Navigation Between Stopovers by Greater White-Fronted Geese: Comparing Compass Mechanisms and Efficiency Benchmarks

Background Long-distance migration in many birds proceeds as a series of chained flight segments between stopovers, each undertaken under shifting winds, light conditions, and geomagnetic contexts. Yet, most analyses still model journeys as continuous paths across entire trips, applying global optima or fixed compass rules and overlooking leg-specific variations. This obscures how conditions at departure reshape headings and route geometry at the segment scale, where decisions are made. Methods We analysed 1524 flight segments (2014–2024) from 122 GPS-tagged greater white-fronted geese ( Anser albifrons ). For each segment, we simulated five biologically plausible compass mechanisms (geographic and geomagnetic loxodromes, magnetoclinic route, time-compensated sun compass, local wind-aligned route) and two efficiency benchmarks (great-circle route, global wind-optimal route). Simulations were initialised with the observed departure bearing, time-aligned to each track, and driven by data on hourly winds and spatiotemporally varying geomagnetic fields. Similarity between observed and simulated routes was quantified using median geodesic distance, dynamic time warping and directional consistency. We then modelled environmental correlates of closest matched routes and tested within-individual repeatability across journeys. Results Efficiency benchmarks showed seasonal structure. In autumn, segments most often matched the global wind-optimal path. In spring, segments more frequently matched the great-circle route. Across seasons, the geographic loxodrome was the most frequent compass match, with magnetoclinic routes commonly second. Geographic and geomagnetic loxodromes often alternated as winner and runner-up with small margins, which indicates structural redundancy. Local wind-aligned routes were least common overall but occurred more often in spring. Alignment patterns varied with tailwind support, departure light regime, short pauses en route and segment position (initial, mid-journey, terminal). No within-individual repeatability was detected for either efficiency class or compass assignment. Conclusions Our results support a multi-cue, context-sensitive navigation process with functional redundancy among compass options and seasonal differences in efficiency alignment. Decisions made at stopovers reshape subsequent legs, arguing for segment-focused modelling to understand how environmental conditions translate into realised routes.