Abstract from BTO Research Report No. 313:

I. Henderson, N. Ravenscroft, N. Clark & S. Holloway (2003)

The Colworth Sustainable Agriculture Project. The Response of Birds, Invertrebrates and Plants to Crop Structure and Management Manipulations on Arable Farmland. ISBN 978-1-906204-20-4

EXECUTIVE SUMMARY

1. Except for Skylark, concentrations of territories tend to be associated with key boundary features including mature trees, scrub or thick hedges.
2. In both summers, oilseed rape and peas were associated with the highest densities of Skylarks (on peas) and Whitethroats and Reed Buntings (in oilseed rape). However, in 2000, peas attracted high densities of other foraging species, particularly when flowering. However, this effect was not so apparent in 2001 with the pea crop located further away from key boundaries. Interestingly, in 2001, most Skylark territories were located on or near to their territories in 2000 (i.e. field 43), suggesting that field location is a powerful variable in territory selection.
3. For Yellowhammers, access to marginal grassy vegetation and bare ground, by tracks and roads, was imperative for adults provisioning young. Among crops, oilseed rape was used in preference to other crops and relatively little use was made of winter cereals. Pre-breeding birds fed extensively on weedy ground or cultivated ground that was oilseed rape in the previous year of the rotation.
4. The baseline survey and the timed counts suggested that there were positive associations with sustainable pesticide areas for several bird species, including Skylark and Linnet (Table 3). Responses to fertiliser inputs were equivocal, while crops following minimal cultivation tended to support slightly lower densities of birds than deep-plough GAP crops.
5. The densities of birds foraging on the SAP area was significantly higher during the second winter (2000/2001) than during the first winter (1999/2000) probably due to the retention of stubble fields in to February and March. Rooks, Jackdaws, Woodpigeons and Stock Doves were particularly abundant during the second winter. Flocks of Skylark, Yellowhammer and Tree Sparrow were especially notable in winter 2 compared to winter 1. Despite high densities of birds in late winter 2001, the numbers of breeding territories of birds did not increase in summer 2001. Skylark, Linnet and Yellowhammer territory densities were high in both years, and within the upper half of the range of densities recorded in previous studies on farmland. Skylarks were especially numerous on oilseed rape in summer 2000, with close to maximum densities for farmland (1.25 birds per hectare or over 0.5 pairs/ha). In 2001, Skylarks avoided rape, probably because of the woodland adjacent to this field. Interestingly, they were more polarised on the previous year’s rape field, that was now spring and winter wheat. Comparable densities to rape in 2000 were recorded in 2001 on the sustainable patch of spring wheat but densities were very low elsewhere on the field (Table 2).

Lapwing and Grey Partridge were recorded too infrequently to judge their relative numbers between years. Both species were scarce on site in both summers and only Grey Partridge breed there in small numbers (perhaps two pair maximum: one pair per 30 ha). In prime arable/grassland marginal habitats they may increase to perhaps five times this density.

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