Livestock species and grazing rotational patterns modulate grassland bird assemblages in Mediterranean drylands

摘要

In the last decades, western Iberian Mediterranean drylands have experienced a shift from extensive sheep to beef-cattle farming. In this 5-year study in Evora region (Southern Portugal), we investigated the role of livestock species in favouring grassland bird habitat suitability, starting from the hypothesis that livestock species complement bird habitat requirements under contrasting grazing rotation patterns and annual rainfall conditions. Field methods were based on bird counts and data was analysed using Generalized Linear Mixed Models. Model ranking and selection were based on the estimation of second-order Akaike Information Criterion (AICc). The grazing rotation pattern was the variable that best explained bird richness and total bird abundance, whereas livestock species had a minor effect. The corn bunting, the common quail and the crested lark presented higher abundances in fields grazed by sheep whereas calandra larks showed opposite trends. Except for the crested lark, grazing rotation pattern was the variable that best explained the abundance of individual species. Fields under short-medium duration rotational grazing revealed lower bird abundance and richness. Interactions between livestock species and grazing rotation were only found for the zitting cisticola. Bird species preferences relative to livestock species were found to be independent of annual rainfall conditions. We conclude that shifting from sheep to cattle grazing in Iberian Mediterranean drylands may favour light to moderate changes in the species identity of grassland bird assemblages (i.e. certain species appear or increase while others decrease or disappear from the assemblage), although no significant changes were found for bird richness. However, the grazing rotational patterns had greater effect on species total abundance and richness than the particular livestock species. Given the alarming decline of grassland birds in Europe, changes in grassland bird assemblages associated to the sheep-to-cattle shift currently occurring in Iberia may become an important issue within the framework of future European agricultural policy and should be subject to long term monitoring.