A PRELIMINARY ASSESSMENT OF SOME FACTORS INFLUENCING THE DENSITY AND DISTRIBUTION OF PALEARCTIC PASSERINE MIGRANTS WINTERING IN THE SAHEL ZONE OF WEST-AFRICA
P. Jones et al., A PRELIMINARY ASSESSMENT OF SOME FACTORS INFLUENCING THE DENSITY AND DISTRIBUTION OF PALEARCTIC PASSERINE MIGRANTS WINTERING IN THE SAHEL ZONE OF WEST-AFRICA, Bird study, 43, 1996, pp. 73-84
Population densities of Palearctic migrant and African birds were esti
mated from 444 point counts, that estimated minimum density, at 10 sit
es in the Sahel zone of northern Nigeria during December-January 1993/
94. In total, 15 Palearctic species were recorded during point counts
averaging 5 species per site, and 76 African species averaging 24 spec
ies per site. The densities of Palearctic migrants varied from 1 bird
ha(-1) in semi-desert and highly degraded woodland, tip to 8 birds ha-
l in dense Sahelian woodland. Common Whitethroats Sylvia communis were
most abundant (up to 0.7 birds ha(-1)) in sites rich in Piliostigma r
eticulata trees; Subalpine Warblers S. cantillans were most abundant (
tip to 5.9 birds ha(-1)) in sites rich in Acacia spp. and Cassia siebe
riana; Lesser Whitethroats S. curruca and Redstarts Phoenicurus phoeni
curus were associated with high overall tree densities (both up to 0.6
birds ha(-1)); Northern Wheatears Oenanthe oenanthe occurred at densi
ties of about 1 bird ha(-1) at very low tree density falling to about
0.25 birds ha(-1) over a wide range of intermediate tree densities. Fa
rmland supported densities of Palearctic migrants up to 6 birds ha(-1)
where large trees or hedgerows remained. The densities of Palearctic
Sylviidae were positively correlated with the combined densities of al
l ecologically similar African species of small insectivorous and/or f
rugivorous passerines: Palearctic warblers were half as common as thei
r African counterparts.