The wintering granivore passerine community in the northern Negev: Patterns and mechanisms

About 20 species of granivorous passerines winter regularly in the northern Negev and about 12 of them can be found in natural scrublands. However, site-specific species assembly may vary markedly between locations within this range. In the present work, the changes in community structure were characterized, and an attempt has been made to assess the ecological basis for these changes. Natural scrubland habitats along geographical, topographical, and climatic gradients were sampled. In each sample, the community and habitat structures were characterized. In addition, I noted various species-specific ecological and behavioral characteristics, such as foraging substrate and reaction to threat. Except for lesser short-toed and desert larks, the general winter distribution range of all species includes the research area. I therefore assumed the regional species pool to be uniform for the whole research area. Habitat structure had a significant effect on the number of species as well as on the general biomass of the bird community: both biomass and number of species are positively correlated with the percent of area covered by annual vegetation. In addition, both biomass and number of species are correlated with the size of the area not covered by bushy vegetation (open area). This covariation appears to be hump-shaped, peaking over habitats characterized by medium-size open areas. The structure of the bird community is affected by the structure of the habitat; species-composition similarity between two locations was found to increase significantly in proportion to the similarity between their habitat structure. The mechanism through which the habitat structure influences the community structure is not yet clear. Nevertheless, it seems that the abundance and distribution of resources as well as the characteristics of the bushy vegetation may play an important role in structuring the bird communities in these habitats.