Crop heterogeneity and non-crop vegetation can enhance avian diversity in a tropical agricultural landscape in southern China

In agricultural landscapes, the positive role of environmental heterogeneity for biodiversity conservation is often assumed. However, with agricultural intensification, opportunities to maintain or restore semi-natural/natural features that produce environmental heterogeneity may be limited. In such a situation, crop heterogeneity could be a way to balance crop production and biodiversity conservation. Despite growing interest in this possibility, few studies have examined whether crop heterogeneity is a major contributor towards environmental heterogeneity in agricultural landscapes in Asia. We investigated how crop heterogeneity, non-crop heterogeneity, and the amount of non-crop vegetation influenced avian diversity in a tropical agricultural landscape in southern China using a hierarchical multi-species occupancy model. We conducted bird and crop surveys during the winter and summer of 2015–2016. Within a 100 m-radius area, we calculated the total length of edges between fields (configurational heterogeneity of croplands) and two Shannon-Wiener diversity indices representing compositional heterogeneity of crop types and of non-crop features (mostly non-crop vegetation). We calculated the amount (i.e., percent cover) of non-crop vegetation within a 500 m-radius area. Crop and non-crop compositional heterogeneity positively influenced species richness in the winter and in the summer, respectively. The amount of non-crop vegetation within the landscape increased species richness in both seasons. Similarly, the occupancy probability of almost half of the species increased with increasing crop compositional heterogeneity or the amount of non-crop vegetation in the winter, and non-crop compositional heterogeneity in the summer. While crop configurational heterogeneity did not show a consistent effect on species richness in either season, it influenced positively the occupancy probability of several open area species in the winter. Our results suggest that crop compositional heterogeneity can have an impact on avian diversity, although its effect varies seasonally, and that the amount of non-crop vegetation at the landscape scale is important for the conservation of avian diversity in tropical agricultural landscapes.