Increases in human population and per capita consumption are placing growing pressures on ecosystems as agricultural demands escalate. This has led a debate about how best to farm for both high yields and biodiversity. Two contrasting models have been put forward: “land sharing”, where low-yield farming enables biodiversity to be maintained within the agricultural landscape, and “land sparing”, where high-yielding agriculture is practiced, requiring a smaller area of land to attain the same yields and therefore leaving greater areas of natural habitat untouched. A new study led by the BTO, in collaboration with NatureUganda, Makerere University, the University of Turin, RSPB and the University of Cambridge, has examined these two models in southern Uganda, an area associated with the cultivation of coffee and bananas. Farmland and forest areas were surveyed, taking in a gradient of agricultural intensification. The population densities of 256 species of bird (including 10 Palearctic migrants) were measured, along with crop yields and farmers’ income. In a result consistent with previous studies in Ghana and India, most birds were found to fare better under land sparing, where more native forest was left unaffected by agriculture. This was especially true of species with smaller geographical ranges, which are more likely to be of conservation concern. However, the authors suggest that high-yield farming can only be effective in delivering land sparing if combined with strong measures to protect natural habitats, other ecosystem services and human livelihoods.

Research by the University of Birmingham and the BTO used data from the Waterways Breeding Bird Survey and the National River Flow Archive to show how the occurrence of river birds is influenced by the magnitude and timing as well as variation (i.e. extreme events) in river flow. Flow affects aquatic communities of invertebrates that birds consume, through changes in velocity, depth, temperature, turbidity and nutrient availability. Such influences on the lower trophic levels have implications for the whole food web, with consequences for river birds in terms of survival and breeding success. Data from 17 river birds were analysed to show that species associated with upland environments (e.g. Grey Wagtail) had a higher probability of occurrence with high flows, while those that forage within aquatic macrophytes (e.g. Coot) preferred stability in low flows, perhaps because an undisturbed substrate promotes greater plant diversity and growth. Species that predominantly forage at river margins (e.g. Lapwing) benefitted from variability in low flows, possibly because this increases the availability of foraging habitat. Dipper, which typically feeds in river channels, also favoured variability in low flows, which may indicate a propensity for this species to forage opportunistically outside breeding territories when marginal habitats are exposed. Flow timing, especially in spring, was important for diving species (e.g. Great Crested Grebe) and bank-nesting species (e.g. Kingfisher). Bank-nesting species may be vulnerable to flow variability during the breeding season, as nest sites on marginal habitats are prone to flooding, but benefit from annual high flows that create suitable breeding habitat of exposed sediment banks. River systems are vulnerable to climate change. Current models predict that river flows in the UK will have altered considerably by 2050, with decreases in summer flows and increases in winter flows. This research helps suggest how bird communities might respond to a climate change-induced shift in river flows and highlights which species will be at risk if the predicted increase in the intensity of floods and droughts comes about.