Seasonal changes in nutritional condition of shorebirds (Charadrii) during the non-breeding seasons
The nutritional condition (fat and protein reserves)of shorebirds was studied, mainly at Teesmouth and Lindisfarne, north-east England, during the non-breeding season. Normal patterns of fat and protein storage are similar in most coastal shorebird species. Fat reserves rise to a peak in midwinter. Fat is stored rapidly before both spring and autumn migrations. Protein reserves (measured as pectoral muscle size) remain steady during winter. Protein reserves increase before spring migration, but not before autumn migration. Most shorebirds regulate both fat and protein reserves during winter. Plovers (Charadriidae) have larger fat and protein reserves than Sandpipers (Scolopacidae). However rocky-shore species carry smaller reserves than species feeding on soft sediments. Interspecific differences are related to morphology, foraging behaviour, habitat use and winter movements. First-year shorebirds carry similar sized or larger reserves than adult conspecifics. Catabolism of nutritional reserves was studied during two periods of severe winter weather in north-east England. Reserves were catabolised faster by species that normally carried the largest regulated reserves. In eastern Britain some Redshanks cannot regulate their fat and protein reserves even during mild winters. Possible reasons are discussed. The condition of shorebirds that had starved to death during severe weather is examined. Redshanks, first-year Oystercatchers, inland species)and shorebirds that return early to breeding grounds are most at risk. Recovery of nutritional condition after starvation is examined. In addition to seasonal variation, differences in the size of regulated fat reserves occur in different wintering grounds. Total lean weights in relation to wing-length as a measure of body size are used to examine whether similar seasonal and latitudinal differences in protein reserves of shorebirds exist. Plovers have larger pectoral muscles than Sandpipers but similar total lean weight (measured in relation to body size). During winter, lean weights are lower in several equatorial and southern hemisphere areas than in northern temperate regions. Seasonal and latitutinal changes in lean weight are discussed in relation to periods of environmental stress.