it is the first work to bring together information discovered during the late 1980s, 1990s and early 21st century on the identification of birds of the large white-headed gull complex. The book adopts a conservative approach at higher taxonomic levels, lumping all gulls (except for ivory gull, Ross's gull and the two kittiwakes) in the genus Larus. A revised taxonomy is adopted at the species level, however; a number of distinctive forms (mainly in the large white-headed gull complex) are regarded as separate species. Species-level taxonomic decisions adopted in the book are as follows: American herring gull (Larus smithsonianus) is treated as a separate species from European herring gull (L. argentatus) Yellow-legged gull (L. michahellis) (including the form atlantis) and Armenian gull (L. armenicus) are treated as separate species from the European herring gull Caspian gull (L. cachinnans) is treated as a separate species from European herring and yellow-legged gulls, and is defined as including the forms barabensis and mongolicus Heuglin's gull (L. heuglini) (including the form taimyrensis) and Vega gull (L. vegae) (including the form birulai) are each given full species status Common gull (L. canus) (including the forms heinei and kamschatensis) and mew gull (L. brachyrhynchus) are treated as separate species. Olsen and Larsson had previously collaborated on two other volumes in the Helm series, on terns and skuas. Errors in the second edition The following is a list of errors in the corrected reprint: On page 21, the illustration of a gull's head, with a pointer highlighting an ear-spot, shows a bird with a full hood; ear-spots are a feature which appears on hooded gulls only when the hood (a feature of breeding plumage) is lost, in winter. On page 27, the caption to figure 14 (an illustration of the spread wingtip of a Caspian gull) describes a "broad white tip" on p9 whereas the figure shows a broad white mirror. On page 496, a report of 14 relict gulls in Ukraine is dated May 2001, whereas these birds were actually seen in May 2000 in the Russia/Kazakhstan border area. On page 276, the picture number 365 is missing (it should show an "Adult summer ssp. argenteus", according to the legend). References Bird field guides