Wing area, wing growth and wing loading of Common Sandpipers Actitis hypoleucos

This study investigates the changes in wing length, area and loading in Common Sandpipers as chicks grow, and as adults add extra mass (during egg-laying or before migration). Common Sandpiper chicks weigh about 17 g and have “hands” that are about 35 mm long at one week old, when the primaries are just emerging from their sheaths. They grow steadily to reach about 40 g, with hands about 85 mm long, at 19 days, when they are just about fledging. Their wings have roughly adult chord width at this age (~53 mm), but they continue to gain primary length (but not much mass) for a week or more, so that wing loading remains at about the same value as in (lean) adults, ~0.32 g/cm2. However, masses increase substantially during egg-laying and as fat accumulates for migration, leading to a 90% increase in wing loading. This may explain the observed reluctance of females to fly during egg-laying. Birds accumulating fat seem more willing to fly; moreover studies on other waders suggest that flight muscle mass increases as the time for migration approaches while other organs shrink, so minimising the potential imbalance between wing loading and power available.