The Rook (corvus Frugilegus L.), Its Nesting in the Slovakia and Relationship towards Agricultural Land

The rook (Corvus frugilegus L.) is one of the greatest corvine birds dependent on open agricultural land. With the onset of spring, hundreds of thousands of rooks flocks which wintered in Slovakia, this area leaves and returns to its breeding grounds in north-eastern Europe. Wintering populations will be replaced by our rooks, in Slovakia nesting, which wintered in France and Spain. Nesting populations of rooks in Slovakia are much smaller, rarer and more vulnerable in comparison with populations wintering in Slovakia. These rooks populations occurs only in vicinity of its breeding colonies, situated mainly in the lowlands and uplands of Slovakia. Many farmers these elegant birds perceive negative, mainly as pests of crops, not as important functional component of agro-ecosystem, where rooks provides important sanitation function, contributes to biodiversity increasing and to biological regulation of pests. Listed function in agro-ecosystems except, but the whole society too, its total usefulness prevails over its harmfulness because rookeries provides nesting opportunities for the critically endangered red-footed falcon (Falco vespertinus L.). Research focused on monitoring of nesting areas of rook was realized in 2010 2013 in the western part of Slovakia in whole area of Podunajská nížina, where natural conditions and agricultural land utilization offers to rook best conditions for its nesting. During evaluated period in monitored territory were situated several tens of rookeries. Some of them, where we noticed active nests, were relatively old and stable. Among such includes rookeries located for example in the cities Trnava, Hlohovec and Piešťany, where rooks have found the most suitable conditions for breeding in the urban environment, in parks on trees. However, rooks were there strongly dependent on the surrounding open agricultural land because of food. We found, that for nest tree selection by rook is not decisive the species only, but mainly height of tree and layout of branches in treetop, which must hold a large number of nests situated close to each other. In these cities there were mainly species: Pinus sylvestris, Platanus acerifolia and Populus nigra. In 2010 in monitored area we noticed 2416 nests, in 2011 the number dropped to 2323 nests, in 2012 increased to 2454 and in 2013 we observed till 2656 nests. The results of research indicate a slight increase of nesting populations of rooks