Includes data for some Namibian species. Seasonal variations in the mass of various wader species are described from data collected mainly in the southwestern Cape from 1970 to 1977. 1Y+ (older than one year) Turnstones Arenaria interpres, Ringed Plovers Charadrius hialicula, Great Sandplovers C. leschenaultii, Grey Plovers Pluvialis squatarola, Knots Calidris canutus Sanderlings C. alba, Terek Sandpipers Xenus cinereus. Common Sandpipers Tringa hypoleucos, March Sandpipers T. stagnatilis, Greenshanks T. nebularia, Bartailed Godwits Limosa lapponica and Whimbrels Numenius phaeopus showed an increase in mass between late March and early May. This was associated with the accumulation of fat deposits as measured in Turnstones and Sanderlings. 1Y-t-Turnstones, Knots and Sanderlings had their smallest mass in mid summer (December and January). Ruffs Philomachus pugnax had a slight rise in mass during the summer, at a time when the seasonal marshes which they inhabit dry out. 1Y (first year) Turnstones, Knots, Sanderlings and Terek Sandpipers which overwinter in the southwestern Cape had a larger mass at this time of the year compared with summer. The mass of post-juvenile Kittlitz's Plovers Charadrius pecuarius and Whitefronted Plovers C. marginatus was also larger during winter than in summer. Two major migration routes are suggested for birds on northward migrations (l)a coastal route along the west coast and then across the Sahara, and (2) a central route to the East African lakes and then through the Middle East. Estimates of the potential flight ranges were made from the amount of fat accumulated prior to northward migration.