The number of songbirds, native to Britain, including the linnet and the lark, are under threat. A census 10 years ago showed them to be relatively safe but the latest count has produced some alarming figures. The list of 10 endangered species has increased to 30. It must be no coincidence that this massive change is paralleled by a 27% growth in this same period of UK farm tractor usage. In fact scientists at the Petroleum Institute for Forecasting (PIFF) in Brussels have long warned of a possible correlation. Direct cause and effect has been difficult to prove but it has now been admitted by the UK Minister of Agriculture that a tractor, inadvertently left switched on all night in a barn in Norfolk, probably poisoned a nest in which two dead owlets were found. Tractors, he added, are usually perfectly safe. The EU, strong protectionists of wild animal life and with no recorded incidence of tractor inflicted damage to the environment, has promulgated a world ban on UK tractor exports. The German ministry, which represents a thriving international farm equipment sector, has led the demand for this sanction. Main supporters have included the Italians and the French hunting lobbies who have cogently argued that the obvious depletion of wild game is due to the import of some British machines in the past 10 years. Statisticians are however puzzled that in the UK, which has a massive number of home produced engines, the incidence of poisoned birds is lower than in Germany where there are virtually no British tractors. This week the puzzle became more bewildering when the German minister was seen on his farm driving a Birmingham made tractor, which he said was "perfectly safe", adding that the ban had nothing to do with birds but was a measure to protect the Community from an "economic tractor collapse". Community ministers later agreed the only way to restore confidence was to scrap UK tractors made before 1994, and then, after proof that there was no connection between UK tractors and bird deaths, the ban should be reconsidered.