Ornithological aspects of conventional and conservation tillage, significance of edges for the occurrence of farmland birds

Abstract

Nearly two-thirds of the territory of Hungary is cropland, about half of the country is arable farmland. These are not only the areas of production, but also habitats for a number of plant and animal species. In our present paper we intend to evaluate the difference between conventional and conservation tillage methods with the aid of birds as biological indicators, since this group adapts to the conditions of the altered environment the quickest way (presence, absence).
We measured in an exact way the difference between tillage types in terms of the abundance of bird species. The latter are used to demonstrate the outstanding role of edges in protecting agricultural habitats. For the experiment we marked out 12 conventional and 12 conservation tilled plots altogether on 107 ha in the vicinity of Dióskál village, in the hilly region of Zala County. The research work was carried out between October 2003 and September 2008, on winter wheat, maize, and oil seed rape fields. Due to the weekly monitoring we were able to follow the variations in the abundance of species. We evaluated winter and summer seasons separately, because the ethological characteristics of birds differ between the two periods.
During the winter season before the autumn tillage roughly the same frequency of occurrence was measured in case of the two types of plots, while after tillage we recorded a 4–29 fold excess on the conservation tilled plots depending on crop rotation. During the summer seasons there was a smaller difference due to the spatial behaviour of farmland birds. Before the insecticide treatment we measured a 1,6–6 fold excess for the benefit of the conservation tilled plots depending on period and crop rotation. After the treatment the number of birds declined and only slowly recovered later with less difference. In case of the most common species we set up abundance variation trends. Direction of the trend showed whether the populations of birds are declining or increasing. A minor decline was recorded in the number of ground nesting farmland birds (skylark, quail), significant decline was revealed in case of species that inhabited edges (Stonechat, Tree Sparrow, Red-Backed Shrike). We determined the longest flight distances measured from the edge of some characteristic winter species. We can state that during winter birds fly up to 200 m away from the edges searching for food, most often they stay close to the edges.
Bird populations of edges useful for agricultural production can only be maintained and even expanded under the protection of boundaries, tree and shrub groups, grass strips both in the qualitative (varied flora, canopy and understory) and quantitative (extension, width) sense.
Our results show that even in intensive agricultural practice it is possible to protect biological diversity by using conservation (non-inversion) tillage.