The Effect of Agricultural Intensification on the Decline of the Corn Bunting Miliaria calandra.

Abstract

The Corn Bunting Miliaria calandra is in steep decline in Britain. In this project I investigated Corn Bunting ecology on lowland farmland in an attempt to identify reasons for this decline. Aspects of ecology investigated included habitat use during the breeding season, nestling diet, foraging behaviour, breeding success, timing of breeding and habitat use during the winter. All investigations sought to identify the influences of farming practice.
Breeding Corn Buntings occupied open arable farmland in the summer, with birds typically found around cereal fields, grassy margins, set-aside and unimproved grassland. Corn Buntings foraging to provision nestlings used habitats with the greatest abundance of chick food invertebrates. These habitats were often cereal fields, unimproved grassland and grassy margins. A low availability of chick food invertebrates appeared costly to breeding success, in terms of nest survival, chick weight and parental effort, while the availability of these invertebrates in crops was related to the use of pesticides.
Timing of breeding appeared to be linked to food availability prior to egg laying, and possibly to the appearance of unripe grain. The length of the breeding season was largely determined by harvest times and the availability of non-cut nesting habitat. Both start date and the length of the breeding season could affect how many breeding attempts could be made.
In winter Corn Buntings fed mostly on cereal grain, which was obtained from stubble fields in early winter, cattle feed in mid-winter and newly drilled spring-sown cereal fields in late winter. The seasonal change in habitat use appeared to be related to the availability of cereal grain, with Corn Buntings changing habitat as more cereal grain became available elsewhere.
A modelling approach suggested that the decline of Corn Buntings apparent on my study site was probably caused by a combination of low nest survival and a Iow number of breeding attempts per year. The national decline of Corn Buntings may also be due to low productivity, but in some areas low over-winter survival may be important. I make recommendations for reversing the decline of Corn Buntings in Britain, which involve implementing sympathetic management measures to increase both productivity and over-winter survival.