Breeding populations of the Hobby Falco subbuteo on farmland in the southern Midlands of England

Site occupancy, dispersion, density and nest sites of Hobbies Falco subbuteo were studied in two areas of farmland in the English southern Midlands between 1975 and 1983. Nesting ranges were identified within which Hobby nests were regularly found but which contained only one pair of birds in any one year. Breeding was not proved in all nesting ranges in every year. Within nesting ranges, birds sometimes used the same nest in consecutive years but nests were also commonly found more than 1 km apart in consecutive years. The mean nearest-known-neighbour distance between simultaneously occupied breeding sites was 4 6 km (range 20-9.6 km) and the minimum estimated densities of Hobbies in the two study areas were 3.8 and 4.8 nesting ranges/100 km. Small inter-nest distances, less than 30 km, were recorded only in the area with the lowest density. Hobbies nested in old Crow Corvus corone nests in a wide range of tree species but prior to the onset of Dutch elm disease, elms Ulmus spp. were probably used almost exclusively in one of the areas. It is concluded that substantial numbers of Hobbies nest on farmland north of the River Thames, outside what has been traditionally regarded as the main range of the species, and that previous published estimates of the size of the British population have been far too low.