BTO First Atlas of Wintering Birds in Britain and Ireland: 1981/82-1983/84
The dataset was used to produce the first BTO/IWC Wintering Birds Atlas (Lack P. (1986) The atlas of wintering birds in Britain and Ireland. T. & A.D. Poyser).
Volunteer (mostly) observers counted the birds they saw during the winter in each 10-km square. The dataset comprises the maximum count seen in a day of each species in each 10-km square in Britain and Ireland.
All of Britain and Ireland, and for the published book but not NBN, including the Channel Islands. All 10-km squares with more than a very small amount of land were visited. Note that Fair Isle (Shetland) was considered to be one 10-km square even though it actually comprises parts of four squares.
To compile as complete a wintering species list as possible for each 10-km square and provide a count of the number of each species seen.
The BTO believes that the maps as published are a true representation of the distribution and relative abundance of each species at a national level, while accepting that there will be some gaps in individual squares, especially for some of the more elusive and rarer species. All 10-km squares which contained reasonable amounts of land except six (1 in England, 5 in Scotland) received the requested minimum of 6 hours of Timed Visits in the field and all six of these and many of those with only small amounts of land received some Supplementary records.
It is known that if observers spend longer in the field in a square then on average a higher number of individuals will be recorded. This potential bias is discussed in some detail in the Introduction to the book and although there is some evidence for some species being recorded more abundantly in squares which received more visits (in turn correlated with human population density) the species most affected are those which are likely to be most commonly associated with humans.
Specific fieldwork was conducted by mainly volunteer observers although professional help was used in some remoter areas.
Two methods of fieldwork were requested from observers:
1) Specific timed visits. An observer visited a 10-km square for a minimum of one hour and was asked to count all the individual birds seen in that time. At the end of the project these counts were standardized to a 'day' defined as 6 hours in the field by using a regression of numbers seen on time spent on a species specific basis.
2) Supplementary Records. Observers were encouraged to send in any and all records of counts of species from 10-km squares. In particular these records were of species not seen on timed visits and those involving high numbers.
The final published maps used the maximum count of each species divided into 3 levels such that 50% of positive records were placed in the lowest category (1), 30% in the middle category (2) and 20% in the highest category (3).
British Trust for Ornithology ([Insert download year]). BTO First Atlas of Wintering Birds in Britain and Ireland: 1981/82-1983/84. Occurrence dataset on the NBN Atlas
Looking up... the number of records that can be accessed through the NBN Atlas. This resource was last checked for updated data on 19 Jul 2022. The most recent data was published on 19 Jul 2022.Click to view records for the BTO First Atlas of Wintering Birds in Britain and Ireland: 1981/82-1983/84 resource.