Variation in bird assemblages along an agricultural intensification gradient: a case study of olive orchards in north-eastern Algeria

Despite the fact that the Mediterranean basin is considered to be a global biodiversity hotspot for flora and fauna, studies investigating the benefits of agri-environmental schemes on biodiversity conservation in perennial agro-ecosystems in this region are scarce, particularly for bird communities in North Africa. This study investigated the effect of agricultural intensification on bird assemblages in olive orchards in north-eastern Algeria. Bird counts were conducted along an agricultural intensification gradient during twelve consecutive months (from March 2014 to February 2015). Accumulation curves and non-parametric estimators for incidence-based data were used to estimate the total species richness of birds. GLMMs, PERMANOVA and non-metric multidimensional scaling analyses were conducted to evaluate and to visualize the variation in species composition among the studied sites during the breeding and non-breeding seasons. Overall, the total species richness of birds decreased with the increasing level of agricultural intensification. Additionally, among the three trophic guilds (insectivore, granivore and omnivore), the frequency of occurrence of insectivorous and granivorous birds tended to decrease with increasing agricultural intensification. We explored possible reasons for the observed patterns, in relation to differences in the intensity of agricultural management, between the olive orchards studied. This study provides the first qualitative data, which suggests that less intensive agriculture can enhance avian diversity, particularly of insectivorous and granivorous birds, in olive orchards in Algeria.