Gizzard and other lean mass components increase, yet Basal Metabolic Rates decrease, when red knots Calidris canutus are shifted from soft to hard‐shelled food

Abstract

We measured basal metabolic rate (BMR), body mass, lean mass, and gizzard mass of captive red knots Calidriscanutusislandica maintained on a trout chow diet (soft‐texture, low ash and water content) for several years and then shifted to small mussels Mytilus edulis (hard‐texture, high ash and water content). During a 3‐week period of feeding on mussels, body mass, lean mass, and gizzard mass increased 7.3 g (+7%), 10.5 g (+12%), and 4.9 g (+213%), respectively, yet BMR decreased from 0.96 to 0.89 W (−8%). Under the new mussel regime, red knots must have reduced the metabolic intensity of some of the tissues. This suggests that the experimental red knots experienced the transition to a mussel diet as stressful and energy limiting, resulting in an energy‐saving strategy by reducing BMR in spite of hypertrophy of the gizzard and other organs.