Effects of season and habitat on bird abundance and diversity in a steppe desert, northern Saudi Arabia

Between 1992 and 1996 the avifauna of the harrat (basalt boulder field) bio tope was quantitatively surveyed using belt transects during all seasons an d in four habitats (wadi, harrat, almost bare, and sparsely vegetated grave l plains) within the Harrat al-Harrah protected area in northern Saudi Arab ia. Twenty species, mostly larks and wheatears, are regularly breeding resi dents, with five species breeding occasionally. Abundance and diversity inc reased in spring and late summer, coinciding with the passage of migrants. The total number of species recorded was 131. Most (70%) resident and non-r esident birds were counted in wadis, which contain the greatest density of vegetation, but no trees or high shrubs. Species richness (Margalef's index ) and diversity (log series alpha) were also highest in wadis. During a sea son when relatively abundant rainfalls were evenly distributed throughout t he season, bird density was marginally higher than in a year of comparative ly poor rainfall, although variation around both figures was large. Compari sons with other areas in Saudi Arabia indicate that increased aridity is as sociated with fewer resident species, but that sites are used by similar nu mbers of migrant species. The structural complexity of vegetation, includin g the presence of trees and grasses, is likely to be the principal factor i nfluencing avifaunal abundance within arid areas. (C) 1999 Academic Press.