The distribution of corn buntings Miliaria calandra in Sussex in relation to crop type and invertebrate abundance.

Abstract

Since 1970, crop types and cereal; invertebrates have been monitored over approximately 62 km² of the Sussex Downs as part of a study of grey partridges. In March 1970, singing male corn buntings were censused over 26 km² of the study area during the spring partridge count. In June 1994, singing male corn buntings were surveyed over 34 km², which included the area surveyed in 1970. Density contours were calculated for the two years. In both years, corn bunting density was highest in areas with rotational grass and spring-sown barley. In 1994, areas of high density also contained higher than average amounts of set-aside land, ungrazed downland grass and winter wheat. Faecal analysis showed that the main invertebrate taxa in the diet of chicks and adults were Arachnida (spiders, harvestmen), Lepidoptera/Symphyta larvae (caterpillars), Carabidae/Elateridae (large beetles) and other Coleoptera (small beetles). All except large beetles were scarcer in 1994 than in 1970. Corn bunting density was positively related to the number of caterpillars in cereal crops. The abundance of caterpillars was highest in spring-sown crops, particularly undersown ones. Corn bunting density was negatively related to the number of Arachnida in cereal crops. Arachnida were more abundant in autumn-sown than in spring-sown crops. High corn bunting density was most strongly associated with traditional rotational mixed farming, which has all but disappeared in the study area and across Britain as a whole in the last 25 years.