Cirl bunting national surveys in the UK

Quality Control

These data have been gathered by trained field-workers and the data are of a high quality. These data have been mapped and checked for sensitivities and typographical/geographical errors.

Method steps

1. The survey area was derived from the occupied tetrads (2km x 2km squares) found in 1989, in addition to those tetrads known to have been occupied in subsequent years. In an attempt to identify potential range expansion, areas around the core tetrads were also surveyed. Each tetrad was visited at least twice during the breeding season. The first visit was made between mid April and the end of May, the second between the beginning of June and the end of August, with a minimum of two weeks between each visit. Some tetrads were visited four times. The tetrads were surveyed by walking public rights-of-way and areas of public open space. Permission to enter private land was sought where necessary. The tetrad coverage was directly comparable with every cirl bunting survey in southern Britain since 1989. Locations of any cirl buntings seen or heard were recorded on a map of the tetrad using standard BTO mapping symbols to denote their behaviour and breeding status. The cirl bunting is a difficult species to detect at very low densities, when song activity may be infrequent. Consequently, there is a possibility that some birds have been missed in tetrads at the edge of the range. The UK population estimate must still be regarded as a minimum as it is likely that concerted search effort allowing unlimited access in the tetrads would pick up more territories. In order to verify records and validate the dataset, the data have been mapped and thoroughly checked. Geographical checks have included comparing the distribution with that shown in the published paper and ensuring that records with the same area name are located close to each other.

The surveys were conducted primarily in Devon and were based on the species' known range. Searches were also carried out in Cornwall, Somerset and the Isle of Wight where there had been recent cirl bunting sightings. Records for Jersey will be provided when mapping for the Channel Islands becomes available on the NBN. The majority of the records are at 100 m resolution. Some records in the 1989 survey are only available at 2 km resolution.