Occurrence of breeding birds and habitat composition in oasis systems: assessment in Tunisia with implications for management planning

In southern Tunisia, oases represent a central component of the landscape. Different types of habitats make up this agroecosystem, hence the importance of investigating their value for local avifauna. In this study, we collected data on bird occurrence and vegetation structure and composition in 1398 plots within 53 oases. The principal component analysis showed significant differences in vegetation structure and composition among the studied oases. Two axes (PC₁ and PC₂) were identified: one (PC₁) represents a gradient of fruit tree dominance, and the other (PC₂) characterizes the nature and representation of the herbaceous stratum. High PC₁ scores are associated with oases dominated by date palm trees, while low PC₁ scores indicate oases dominated by fruit trees other than date palms. High PC₂ scores describe oases with a natural herbaceous layer, while low PC₂ scores embody those with a cultivated herbaceous layer. Then, using the generalized linear mixed model, we assessed the effects of PC₁ and PC₂ on the occurrence of 17 breeding bird species. Four groups of bird species with contrasted ecological affinities were thus identified. The first group (represented by two species) was exclusively affected by the PC₁ axis. The second group (eight species) was affected by the additive effect of PC₁ and PC₂. The third group (five species) depended on the interactive effect of PC₁ and PC₂, and finally, two species (fourth group) were neither dependent on PC₁ nor PC₂. Overall, our results highlight the pertinence of oasis habitat composition for predicting breeding bird occurrence that should be considered by oasis managers to promote biodiversity conservation in these Mediterranean agroecosystems.