Catabolic enzyme activities in the pectoralis muscle of premigratory and migratory juvenile Reed Warblers Acrocephalus scirpaceus (Herm.).

Differences in catabolic capacity in the pectoralis major muscle of premigratory and migratory Reed Warblers were examined. The oxidative capacity was greater in the migratory birds, probably reflecting a "training effect" caused by the increased locomotion activity just prior to migration.Fatty acid oxidation was already high in the premigratory birds, possibly reflecting a saving of carbohydrate for anabolic purposes (feather growth) during the moult. Glycolytic capacity was slightly increased in the migratory birds, suggesting an increased carbohydrate oxidation during migration in spite of the great contribution of fatty acid oxidation.

Seasonal variation in catabolic enzyme activities in breast muscle of some migratory birds.

Five bird species were examined in order to ascertain if any changes in flight muscle catabolism take place between breeding season and migration. Two different patterns were discovered. The first consists of a high oxidative capacity and a low glycolytic and anaerobic capacity during migration. The converse occurs during the breeding season, i.e. low oxidative, high glycolytic and anaerobic capacity. The pattern was found in those species that deposit large amounts of fat prior to migration. The second pattern was similar to the first, but there was no change in fatty acid oxidation capacity between breeding season and migration. The pattern was found in those species that do not deposit much fat towards migration. These changes are believed to reflect differences in migration strategy and differences in locomotory activity during different seasons. Deviations from these patterns are discussed.