Stubble height affects the use of stubble fields by farmland birds
Simon J. Butler, Edward Grey Institute of Field Ornithology, Zoology Department, South Parks Road, Oxford OX1 3PS, UK (fax +44 1865 271221; e-mail email@example.com).
- 1In the UK, over-wintered stubbles are an important foraging habitat for farmland birds, many of which are of current conservation concern. Maximizing the value of stubbles for farmland birds has largely focused on increasing food abundance but has ignored other aspects of foraging behaviour, such as predator avoidance and vigilance.
- 2In this study we investigated the effects of stubble height reduction on seed depletion and the within-field distribution of farmland birds. Stubble on one half of each of 20 fields was topped to lower vegetation height, while the other half was left untouched to act as a control area.
- 3The abundance of granivorous passerines and invertebrate feeders was higher on treatment plots, which had undergone stubble height reduction, while the abundance of skylark and partridges was higher on control plots. Topping had no effect on the within-field distribution of either corvids or pigeons.
- 4Seed densities on both plot types fell between November and March, but there was no significant difference in levels of depletion between treatment and control plots.
- 5For many species, food accessibility and detectability are likely to have been higher, and thermo-energetic and mobility costs lower, on treatment plots. Stubble height reduction could have led to either an increase or a decrease in associated predation risk, depending on the predator escape strategy of a species. Granivorous passerines, which flee to cover, are likely to have benefited from the reduced visual obstruction on treatment plots, while partridges, which rely on crypsis, will have benefited from the greater protection offered by the longer vegetation in control plots.
- 6Synthesis and applications. Increasing the structural heterogeneity of over-wintered stubble is likely to increase its value as a foraging habitat, making it better suited to the foraging requirements and predator escape strategies of a greater diversity of species. Incorporating explicit management options into agri-environment schemes, such as the new Environmental Stewardship Scheme, may represent a cost-effective strategy to achieve this.