Department of Wildlife, Fish, and Conservation Biology, University of California, 1088 Academic Surge, 455 Crocker Lane, Davis, California, 95616, USA.
Department of Entomology, University of Kentucky, Lexington, Kentucky, 40546, USA.
Ecol Appl. 2020 Jul;30(5):e02115. doi: 10.1002/eap.2115. Epub 2020 Apr 15.
Some birds are viewed as pests and vectors of foodborne pathogens in farmlands, yet birds also benefit growers by consuming pests. While many growers seek to prevent birds from accessing their farms, few studies have attempted to quantify the net effects of bird services and disservices, let alone how net effects shift across farm management strategies. We quantified the net effect of birds on crop production across 20 California strawberry (Fragaria × ananassa) farms that varied in local management practices and landscape context. We surveyed farms for berry damage and bird droppings (as potential sources of pathogens) and implemented a large-scale exclusion experiment to quantify the impact of birds on production. We found that birds had only a slightly negative overall impact on strawberry production, reducing economic value by 3.6%. Direct bird damage and intraguild predation contributed equally to this net effect, underscoring the importance of indirect trophic interactions that may be less apparent to growers. In simple landscapes (e.g., low proportions of surrounding seminatural habitat), birds provided pest control in the interiors of farm fields, and costs from bird damage to crops peaked at field edges. In complex landscapes (e.g., high proportions of seminatural habitat), birds were more likely to disrupt pest control by feeding as intraguild predators. Nonetheless, seminatural habitat dampened bird services and disservices, and our models predicted that removing habitat around farm fields would increase costs from bird damage to crops by up to 76%. Fecal contamination of crops was extremely rare (0.01%). However, both fecal contamination and bird damage did increase on farms with higher densities of fencing and wires, where birds often perch. Our results demonstrate that maintaining seminatural habitat around farms may enhance bird diversity and mitigate bird damage without increasing food safety risks. We also show that the net effects of birds depend on farming context and vary in complex ways in relation to locations within a farm, local farm attributes, and the surrounding landscape. This context-specific variation must be considered in order to optimize the management of wild birds in agroecosystems.
一些鸟类在农田中被视为害虫和食源性病原体的传播者，但它们也通过捕食害虫而有益于种植者。尽管许多种植者试图阻止鸟类进入他们的农场，但很少有研究试图量化鸟类服务和危害的净效应，更不用说净效应如何在农场管理策略中发生变化。我们通过 20 个加利福尼亚草莓（Fragaria ×ananassa）农场来量化鸟类对作物生产的净效应，这些农场在当地管理实践和景观背景方面存在差异。我们调查了农场的浆果受损情况和鸟类粪便（作为潜在病原体来源），并实施了大规模的排除实验来量化鸟类对生产的影响。我们发现，鸟类对草莓生产的总体影响仅略为负面，使经济价值减少了 3.6%。直接的鸟类损害和种内捕食对这种净效应贡献相同，这凸显了间接的营养相互作用的重要性，而这些相互作用对种植者来说可能不太明显。在简单的景观（例如，周围半自然生境的比例较低）中，鸟类在农场田地内部提供害虫控制，而鸟类对作物的损害成本在田地边缘达到峰值。在复杂的景观（例如，半自然生境的比例较高）中，鸟类更有可能通过作为种内捕食者来破坏害虫控制。尽管如此，半自然生境减轻了鸟类的服务和危害，我们的模型预测，在农场田地周围去除生境可能会使鸟类对作物的损害成本增加高达 76%。作物的粪便污染极其罕见（0.01%）。然而，在围网和电线密度较高的农场中，鸟类经常栖息的地方，粪便污染和鸟类损害都有所增加。我们的研究结果表明，在农场周围维持半自然生境可能会提高鸟类多样性，并减轻鸟类损害，而不会增加食品安全风险。我们还表明，鸟类的净效应取决于农业背景，并以与农场内部位置、当地农场属性和周围景观相关的复杂方式发生变化。为了优化在农业生态系统中对野生鸟类的管理，必须考虑这种特定于上下文的变化。
