Spring migration strategies of Anas platyrhynchos (Mallard) necessitate individual time-energy trade-offs despite wintering origins or migratory destinations

Abstract

Spring migration is hypothesized to be time-constrained because of competition for optimal nesting and brood-rearing sites. Therefore, individuals are predicted to minimize migration time to breeding destinations; however, migration strategies likely lie on a continuum based on wintering and stopover habitat quality, environmental conditions, or individual-level factors. In other words, individuals and wintering subpopulations may differentially prioritize time-energy trade-offs during migration depending on where they are from, when they leave, and where they are going. We tested these hypotheses by characterizing spatial and temporal variation in spring migration strategies in female Anas platyrhynchos (Mallards), using global positioning system (GPS) data from ~150 individuals captured across the Mississippi Alluvial Valley and Gulf Coast Chenier Plain, USA. We used principal components analysis to classify a series of migratory behaviors into distinct time- and energy-minimization migration strategies, and tested whether migration strategies were related to wintering origins (habitat quality or latitudinal differences influencing migration initiation), migratory destinations (resource predictability), and individual-level factors (age and body condition). Additionally, we estimated individual and wintering subpopulation space-use to identify geographic regions of high and overlapping use that may facilitate time- or energy-minimizing migration strategies. Our results indicated a gradient of time-minimization migration strategies but migration strategy was not influenced by wintering origins nor migratory destination. Instead, time-energy trade-offs manifested at the individual level with time-minimization depending on experience and body condition. We also revealed stopovers and migration corridors of continental importance for spring-migrating A. platyrhynchos and space-use therein suggested migration strategies varied spatially with increasing time-minimization behavior as A. platyrhynchos neared their breeding grounds. Future research should link migration strategies and settling patterns to demographic rates.