The species-specific rate of mass gain in juvenile waders during southward migration under ad libitum feeding conditions

Foraging habitat preferences and migration route selection in avian migrants may correlate with the accumulation of energy stores and their expenditure, which in turn influence migrants’ ability to cover distances between staging sites and shape migratory strategies. Recognizing the diverse energy requirements inherent in various wader species employing distinct migration strategies and routes during their southward migration, we conducted an experiment comparing the rate of body mass gain among juveniles of five wader species—Dunlin (Calidris alpina), Curlew Sandpiper (Calidris ferruginea), Common Ringed Plover (Charadrius hiaticula), Common Redshank (Tringa totanus), and Red Knot (Calidris canutus)—under controlled feeding conditions with unrestricted access to food. There was significant variability in body mass gain rates and refueling. The highest rate of body mass increase and final mass gain was documented in a long-distance migrant known for its non-stop flights and occasional inland stopovers, i.e., the Curlew Sandpiper, while the lowest was in the Common Ringed Plover, a species with a shorter migration distance and frequent coastal stopovers. The observed differences in body mass gain rates among inexperienced juveniles of different wader species under optimal and stable feeding conditions likely reflect species/population-specific adaptations to their migration strategies and the flyways they use. These differences are likely the result of inherited traits shaped by evolutionary pressures.