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Influence of grazing on predation risk in grassland birds

Swakman, V (2011) Influence of grazing on predation risk in grassland birds. Bachelor's Thesis, Biology.

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Populations of many grassland bird species have declined in the last decades. Agricultural intensification and particularly higher grazing pressures have been associated with these declines. Herbivore grazing alters habitat structure and how it influences the possibility for birds to optimise their predator avoiding strategy, is reviewed here. In general, due to heavy grazing pressure swards become homogeneous, this leads to “bowling green” swards, with low variation in vegetation structure and composition. Moderate grazing creates structurally diverse swards and low intensity grazing creates an even greater heterogeneity in vegetation structure and composition. No grazing leads to tree sapling establishment and afforestation. Bird species with different anti-predator strategies react differently on changes caused by grazing. For these four categories of birds; ‘Grassland birds with aggressive anti-predator behaviour’, ‘Grassland birds with low anti-predator behaviour’, ‘Crypsis relying ground feeders’ and ‘Cover-seeking ground feeders’, the effects of grazing on their predation risk is being investigated. Two main differences are being observed, some birds need their view to be unobstructed to notice possible predators, they benefit thus from short vegetation, other birds value the presence of taller vegetation as cover, to go unnoticed by predators. Effects differ per group of species, but generally speaking, habitats with a complex vegetation structure, as a result of low or intermediate herbivore grazing, can support a higher diversity of bird species.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Biology
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 07:46
Last Modified: 15 Feb 2018 07:46

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