Landscape context outweighs field-scale features in structuring bird communities in West African smallholder rice agroecosystems

Abstract. Understanding how local management and landscape structure influence biodiversity in tropical croplands is crucial for reconciling food production and conservation. Here, we examined how field- and landscape-scale characteristics relate to bird species richness in lowland rain-fed rice fields of northern Guinea-Bissau. Birds were surveyed along nine transects repeatedly sampled during two rice-growing cycles (2021–2022), and species were assigned to four trophic guilds: frugivores, granivores, invertivores, and omnivores. Field variables (parcel area, tree cover, field width) and landscape metrics (fragmentation, diversity, edge complexity) were derived from satellite imagery across multiple spatial scales. Species richness for each transect survey was estimated using Bayesian models, and linear mixed models were used to relate richness to environmental predictors and to principal ecological gradients summarizing field- and landscape-level structure. A total of 150 bird species were identified, with an estimated mean species richness of 18.2 species per transect survey. At the field scale, tree cover increased invertivore and frugivore richness by 17.0 % and 16.4 % of the standard deviation, respectively, while wider fields supported higher overall richness and higher richness of granivores and omnivores, with increases of 2.9 %, 5.6 %, 18.4 %, and 14.0 % of the standard deviation, respectively. At the landscape level, bird richness varied with composition and configuration in a scale- and guild-dependent manner: frugivores, invertivores, and omnivores responded primarily at broader scales (1600 m radius around the rice fields), whereas the entire community and granivores showed stronger associations with intermediate-scale attributes (800 m radius). When jointly considering field- and landscape-scale attributes, bird richness showed stronger associations with landscape-scale gradients than with field-scale characteristics. Landscape characteristics significantly influenced the richness of the entire community as well as all trophic guilds considered. In contrast, field-level features affected only frugivores, invertivores, and omnivores, with the richness of these guilds increasing with field openness. These results highlight the context-dependent ecological meaning of commonly used heterogeneity metrics and suggest that sustaining bird richness in smallholder rice systems is likely to benefit from landscape-level planning complemented by field-scale management actions, such as retaining scattered trees.