Steppe bird abundances in fields with agro-environmental schemes and proper controls in Spain [Dataset]

Pairs of nearby fields of similar size, shape, landscape context, and with the same growing cereal crop were selected. One field of each pair was farmed according to the regionally designed agri-environmental scheme (focal field), and the other in a conventional way (control field). Bird counts in each field were made by experienced ornithologists on sampling plots of 12.5 ha centered on each field. Counts were limited to a 12.5 ha fraction of the field if it was larger, and included birds in the surrounding fields within the boundaries of an extended 12.5 ha sampling plot if it was smaller. No fields under agri-environmental scheme management were included in control plots. Territorial birds were counted during the breeding seasons (April-June) of 2010, 2011 and 2012 using the territory mapping method. Each sampling plot was surveyed four times during the breeding season at ca. two-week intervals, and all individual birds detected by sight or sound during a 25-min survey of the whole plot were mapped. Surveys took place during the first hours after sunrise in days of fine weather. The same observer surveyed the sampling plots of a given pair on the same day. Post-breeding (July-September) and winter (December-February) abundances were estimated in 2010 and 2011. Line transects that covered fully each study plot were walked at low speed early in the morning (from sunrise to 11:00 a.m. in summer and from 8:00 a.m. to 13:00 in winter) in days of fine weather, counting all birds seen or heard taking care to avoid double records. Transects were repeated three times at 3-4 week intervals both in summer and in winter. As in spring, the same observer surveyed the sampling plots of a given field pair on the same day. Data for bird species other than steppic, open-land birds (the ones that were targeted by the evaluated schemes) are not given