FAT, WATER, WEIGHTS AND WING‐LENGTHS OF AUTUMN MIGRANTS IN TRANSIT ON THE NORTHWEST COAST OF EGYPT

Data are presented for the fat and water contents of 410 specimens of 11 species of trans‐Saharan migrants collected on the northwest coast of Egypt in autumn. Mean fat contents vary from 37% of lean dry weight in Hirundo rustica to 110% in Sylvia communis. There is also much variation in the range of fat contents within individual species, Muscicapa striata and Lanius collurio being exceptionally closely grouped and P. phoenicurus widely dispersed. The results for each species are discussed in relation to their migratory circumstances. On the basis that the birds concerned would have started to cross the eastern Mediterranean with at least 11/2 times as much fat as they contained on landing in Egypt, comparisons are made with data for spring migrants in western Africa and with American trans‐Gulf migrants. Water contents, discussed as % of lean dry weight, show considerable variation within each species:the coefficient correlating this percentage with % fat is around 0.50 except in Lanius (0.98) and Oriolus (0.92). On investigating the relationship between wing‐length and lean dry weight, we did not find a strong correlation in any of the species and caution in accepting conclusions to the contrary is indicated. Copyright © 1970, Wiley Blackwell. All rights reserved