Spatial and temporal distribution of breeding Skylarks Alauda arvensis in relation to crop type in periods of population increase and decrease .

The seasonal variation in Skylark Alauda arvensis occurrence, in terms of both presence and abundance, was examined in relation to crop type on a number of survey sites in English lowland farmland in two periods, 1965-70 and 1990-95 . These two periods were selected to coincide with periods of population increase and decline respectively. We were able to consider the effects of changes in cropping regime on the length of the breeding season for Skylarks, a factor implicated in the cause of the Skylark population decline . The overall occurrence of Skylarks was significantly lower in the 1990-95 period, in accord with national trends . At the farm level, Skylark abundance increased significantly with crop diversity . There was little difference between spring and winter cereals in occupancy rates or seasonal trend in the 1965-70 period, but in the 1990-95 period, territories were abandoned much later on spring cereals than on winter cereals . Spring cereals were abandoned later in the season in the 1990s than the 1960s whereas winter cereals were abandoned earlier. There was thus an indication that the suitability of winter cereals had decreased between the two periods . However, in the 1990-95 period, farms with spring cereals tended to have more diverse cropping than those without, so the results for this crop may be confounded by farm-level effects . Set-aside, which only occurred in the 1990-95 period, had the highest rates of Skylark occurrence, but showed no seasonal trends. These results broadly support the suggestion that increases in winter cereals and loss of farm habitat diversity have contributed to the Skylark decline

Chamberlain D .E ., J.A . Vickery & S . Gough 2000, Ardea 88(1) : 61-7 3