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) biotope was quantitatively surveyed using belt transects during all seasons and in four habitats (wadi, harrat, almost bare, and sparsely vegetated gravel plains) within the Harrat al-Harrah protected area in northern Saudi Arabia. Twenty species, mostly larks and wheatears, are regularly breeding residents, with five species breeding occasionally. Abundance and diversity increased in spring and late summer, coinciding with the passage of migrants. The total number of species recorded was 131. Most (70%) resident and non-resident birds were counted in wadis, which contain the greatest density of vegetation, but no trees or high shrubs. Species richness (Margalefʹs index) and diversity (log series alpha) were also highest in wadis. During a season when relatively abundant rainfalls were evenly distributed throughout the season, bird density was marginally higher than in a year of comparatively poor rainfall, although variation around both figures was large. Comparisons with other areas in Saudi Arabia indicate that increased aridity is associated with fewer resident species, but that sites are used by similar numbers of migrant species. The structural complexity of vegetation, including the presence of trees and grasses, is likely to be the principal factor influencing avifaunal abundance within arid areas.