GUGLIELMO, C.G.*; PIERSMA, T.; WILLIAMS, T.D.: Flight-Induced Muscle Damage And Avian Migration, Evidence From Two Shorebird Species

It has often been suggested that birds undergo processes of repair and physiological recovery following long distance flights, however exactly what these processes are remains mostly undescribed. High intensity, long duration exercise is known to cause muscle damage, which is a pathological phenomenon qualitatively different from the mobilization of amino acids as fuel. Acute muscle damage results in the disruption of muscle ultrastructure, leakage of muscle proteins into the blood, immune system response, soreness, edema, stiffness and reduced strength. Chronic damage may lead to immunosuppression. We investigated muscle damage in two species of long-distance migrant shorebirds by measuring plasma creatine kinase (CK) activity. In the Western Sandpiper (Calidris mauri), a non-synchronous, short-hop migrant, plasma CK was higher in migrants than non-migrants in two years of study. Plasma CK was higher in relatively untrained juveniles making their first migration than in adults. Bar-tailed Godwits (Limosa lapponica) migrate relatively synchronously and make a single 4300km (60 hrs) flight from West Africa to the Wadden Sea in The Netherlands. Plasma CK was highest following arrival at the Wadden Sea and declined during the one month stopover period. Godwits identified as late arrivals based on plumage characteristics had significantly higher plasma CK than early arrivals. In both model systems elevated plasma CK indicated that muscle damage occurs during migration. However, the relative increase in CK was modest compared to that known to indicate loss of function in other animals. High costs of muscle damage (e.g. predation risk) could lead to strong selection for mechanisms to avoid it.