Bird Atlas 2007-11

I suspect most Birdwatch readers will have been anticipating this mighty tome for some time, and many will have contributed results from their own timed transects to help build up the copious data used to complete the five-year project.

Probably the largest-scale bird survey undertaken anywhere in the world to date, the information in the book took more than 40,000 volunteer surveyors (as well as several other reliable sources) four summer and winter seasons to accumulate, and the results bear out this incredible effort. The distribution of almost 300 British species over the five years – including the entirety of our breeding avifauna plus regular wintering birds – is presented in a spacious, easy-to-read format comprised of a photograph or two of the bird in question, some basic analytical text and anywhere between one and six maps.

These last are the meat of the book, representing variously the distribution, distribution change since previous atlases (breeding atlases for the periods 1968-72 and 1988-91), relative abundance and relative abundance change of breeding species, and the distribution and changes since the previous winter atlas (1981-84).

The layout of the book is logical. The 156 pages of introductory text is informative, starting with an introduction, glossary and standard references. It then leads into an exhaustive (and somewhat exhausting for the layman, I suspect) itemisation of the background, organisation, survey methods, data capture and analysis, and detailing of problems and lessons learnt.

Dividing Britain and Ireland into 10-km squares, very few were omitted (though understandably more were covered more intensively in summer). In fact in winter, just 0.02 per cent of the land area remained uncovered, with this figure dropping even further in summer to 0.004 per cent.

A lengthy chapter analysing trends in the islands’ avifauna presents the overall patterns of change, as well as changes in species grouped by habitat specialisation and broader taxonomic relationship; for instance, we can see how farmland or wetland birds have fared, or conversely raptors and waders.

While there is not enough room here to summarise all the information contained in the book, there have certainly been substantial range shifts in many species since the last atlas. Bearing in mind that the new volume doesn’t deal with population in terms of numbers of individuals, there have been range shifts north-west in Grasshopper and Garden Warblers, east in Green Woodpecker and Stock Dove, and a retraction south-east in Nightingale and European Turtle Dove. Upland species with nowhere to go have suffered range contractions probably due to climate change, and may reach vanishing point in the ensuing century.

As ever, it is the species accounts which hold the most revelation for the ordinary birder, and these come thick and fast. However, the sparseness of some winter visitors such as Arctic Redpoll and Lesser White-fronted Goose may raise questions as to why they are included, while there are maps for Zitting Cisticola and Short-toed Treecreeper based on their presence in the Channel Islands. Again, quizzical expressions may be donned when the reader sees maps for the likes of Swan Goose, Wood Duck, Helmeted Guineafowl and Indian Peafowl.

Outside the questions of birders’ lists, however, all the aforementioned species need to be monitored as they are wintering or breeding in some numbers in Britain, and any increases, shifts or declines are informative for the future (although there is an argument for taking these species out of the main accounts as an appendix).

It is also noteworthy that results derived from anything other than a specialist crossbill survey have caused Common and Scottish Crossbill data to be combined on one map, underlining the extreme difficulty of identifying the latter species in the field. Also, the occasional form such as Bean Goose that is now routinely split remains lumped in the text, occluding meaningful comparison in future.

The maps are as detailed as one would hope. However, there may have been a graphical method of combining most into one or two larger maps allowing room for more detailed analysis in the text, which can sometimes be a little over-generalised.

There is also a slight problem with the size of the possible, probable and confirmed breeding dots in the legend to each summer map, which differ in size to those on the actual maps and cause confusion as to the local status of each species at first glance. A helpful quick reference to the map symbols is well placed on the inside front cover.

But these are minor quibbles considering the breadth of the work, which will be both invaluable and seminal to professional ornithologists and birders alike, and should take pride of place next to that other essential BTO tome, The Migration Atlas (2002).

The necessity of producing the atlas, and indeed continuing to amass the data in another 10 years or so, is illustrated by the fairly healthy status indicated on the maps for Dartford Warbler and Kingfisher, in both of which birders have anecdotally noticed substantial declines over the last couple of winters, and which may need more nationwide assessment soon.

• Bird Atlas 2007-11 by Dawn Balmer, Simon Gillings, Brian Caffrey, Bob Swann, Iain Downie and Rob Fuller (BTO Books, Thetford, 2013).
• 720 pages, more than 1,300 maps and numerous colour illustrations, tables, figures and colour photographs.
• ISBN 9781908581280. Hbk, £70. Birdwatch Bookshop from £64.99.