Spring weights of some Palaearctic passerines in Ethiopia and Kenya: evidence for important migration staging areas in eastern Ethiopia

Abstract

Palaearctic migrants were trapped in late April and early May at a passage site near Jijiga in eastern Ethiopia. Willow Warblers Phylloscopus trochilus and Spotted Flycatchers Muscicapa striata were predominant, while Red-backed Shrikes Lanius collurio, Sedge Warblers Acrocephalus schoenobaenus, Reed Warblers A. scirpaceus, Garden Warblers Sylvia borin and Common Whitethroats S. communis also featured prominently. Weights were high in all species, and over 70% of the birds caught were extremely fat. Spring weights and fat scores at Jijiga were compared with those found in the same species in Kenya, and the difference was striking. In Kenya, most species had mean spring weights 10–20% above lean weight; at Jijiga, species’ mean weights ranged from 30% to 55% above lean weight. Whereas the reserves of most migrants departing from Kenya would have supported flights only as far as Ethiopia, the fat loads of birds at Jijiga indicated a potential for crossing Arabia with little need to feed. This suggests important staging and fattening grounds between these two areas, perhaps in the Acacia–Commiphora bushlands drained by the upper Juba and Shebelle rivers and their tributaries.