Second Atlas of Breeding Birds in Pennsylvania

This nicely-produced book, detailing the distribution of 190 species found breeding in the state of Pennsylvania during 2004-09, is a great credit to the editors and organisers, and to the 2,000 participants in this citizen-science enterprise. An important extra dimension came from the state funding that allowed employment of trained field crews to conduct point counts at more than 34,000 locations, covering almost every block in the whole state. These surveys yielded density maps and state abundance figures for the 115 most numerous diurnal species, with the totals ‘back-casted’ using over forty years using trends from the Breeding Bird Survey. Indeed, changes in distribution and abundance are key themes of this book as the project followed the widely-accepted twenty-year cycle and much of the interest lies in the manifold differences from the first, 1983-89, atlas.

The accounts of individual species, the bulk of the book, are interesting and informative, though I was surprised that relatively few of them considered, perhaps from lack of information, what happens to birds outside the breeding season: most quit the frozen state in winter so that conditions elsewhere must surely have a big effect on survival and populations. I was pleased to read the substantial chapter on conservation, while the plots of habitat associations and altitude for 120 species will surely repay further detailed study. The meticulous analyses of methodology and results provide much food for thought. For instance, some species are shifting their distribution to the north while others are spreading south, although altitude in the Appalachian Mountains is often at least as big a factor as latitude.

This book will surely appeal to those of us who like atlases, but why would it interest other British birdwatchers? At first, there would seem to be little in common between a land-locked, heavily-wooded American state and a mostly agricultural European island, but on my ten visits to the state in the last decade – including spending time with some of the Atlas team – I have become increasingly intrigued by the similarities and differences between the Pennsylvanian and British avifaunas.

This Atlas shows that several of the species that have most markedly increased their distribution and population have done likewise in the UK, such as Canada Goose, Raven and Cormorant (albeit a different species of the latter). Rachel Carson, the Pennsylvanian author of Silent Spring, would surely have been pleased to see birds recovering well from the pesticide era, including Peregrine, Osprey, Goosander and Bald Eagle. For declining species, some of the reasons are familiar to British ornithologists, including changes in land-use, such as earlier cutting of agricultural grassland (hitting meadowlarks and some sparrows); the loss of scrub; and the high populations of deer in some of the state’s forests that have trashed the understorey. Other causes of declines are all-but unknown here including hybridisation (Golden- and Blue-winged Warblers); brood-parasitism (Brown-headed Cowbirds and many warblers); disease (West Nile Virus has probably hit the numbers of the larger owls); and loss of habitat to opencast mining, although regenerating grassland provides new opportunities for some species.

To tempt the British reader further, other snippets include that Pennsylvanian Pheasants have declined to one-quarter of their total twenty years ago, while Wild Turkey has increased more than fourfold; there are more Starlings breeding in PA (2 million pairs) than in the UK (1.8 million); Collared Dove has recently arrived – watch out Pennsylvanians!; and that even now there are more Ruddy Ducks in the UK, a species not confirmed breeding in the state since 1998. Finally, can anyone explain the mathematical curiosity that the density of breeding birds in Pennsylvania (42 million pairs in 119,300 km²) is virtually the same as in the UK (84 million pairs in 243,600 km² (Musgove et al British Birds February 2013))?

Book reviewed by David Norman