Thames and Chiltern Bird Atlas

This website for the Thames and Chiltern Bird Atlas brings together the results of a number of projects which together provide information on changes in the distribution of the breeding birds of over 9000 square kilometres of inland southern England, the density of breeding and wintering birds and habitat information for the area.

Its aim is to provide a source of information for birdwatchers and naturalists interested in the wildlife of their area, a reference source for local policy makers assessing the species and sites whose conservation should be promoted and a source of information for scientists researching population changes and density and their relationship to habitats.

The Area Covered

The information covers the inland counties of Bedfordshire, Berkshire, Buckinghamshire, Oxfordshire and Hertfordshire. From north to south it encompasses part of the southern Cotswolds, the vales of White Horse and Aylesbury, the chalk hills of the Chilterns and Berkshire Downs and valleys of the Thames and some of its southern tributaries. It includes substantial urban areas, such as Reading, Oxford, Luton and Milton Keynes; the outer metropolitan suburbs and a variety of habitat types. It is an area which has seen substantial changes in the 20th Century, in both rural and urban areas and these changes continue.

The Sources

The information is derived from the following:-

Breeding Distribution Data

All of the counties undertook breeding bird distribution atlas surveys between the early 1980s and the early 1990s, plotting distributions and breeding evidence by reference to tetrads (2km x 2km squares), each comprising four 1km squares from the Ordnance Survey's National Grid. When the BTO generously made available for local atlas projects its web-based data capture system developed for Bird Atlas 2007-11, the five counties repeated their earlier surveys. As a result we can now show the changes in the distribution of the breeding species since the 1980s.

Winter Distribution Data

The national Bird Atlas 2007-11 project also collected distribution information for November-February across the four winters. All five counties in this region also undertook that fieldwork at the tetrad scale.

Relative Abundance Data

Results from the timed tetrad visits (TTVs) undertaken during fieldwork for Bird Atlas 2007-11 have been used to calculate relative abundance estimates. Four timed visits (of one or two hours) were undertaken, two in the breeding season and two in winter, during which all birds encountered were counted. For Bird Atlas 2007-11 all that was required, to map abundance at a national scale, were counts from a sample of 8 of the 25 tetrads in each 10km National Grid square. In Berkshire, Buckinghamshire, Oxfordshire and Hertfordshire the local organisers aimed to cover all tetrads, and results are presented here.

Habitat Information

The information used for the habitat comparion maps is derived from 1km habitat mapping carried out by the Centre for Ecology and Hydrology, which has been combined to provide tetrad-level assessments.


The organisers of this website gratefully acknowledge the contributions of

  • BTO, who by making their resources available for local bird atlas projects made possible the collection, collation and review of data upon which much of this website is based
  • The organisers of, and participators in, the local atlas projects whose many hours of hard work produced the data presented here
  • The local clubs (Berkshire Ornithological Club, Oxford Ornithological Society, Buckinghamshire Bird Club, Herts Bird Club, Bedfordshire Bird Club, Newbury District Ornithological Club, Banbury Ornithological Society) for their support for the atlas surveys and this website
  • The Thames Valley Environmental Records Centre (TVERC) for their financial support
  • Andrew Moon for permission to use his photographs
  • Garganey Consulting for designing and producing this website


BTO logo


Bedfordshire Bird Club logo


Berkshire Ornithological Club logo


Buckinghamshire Bird Club logo


Herts Bird Club logo


Oxford Ornithological Society logo


ThamesValleyERC logo218