Monday, March 09, 2009

Review of The Second Atlas of Breeding Birds in New York State

A new resource is now available for studying the birds of New York state. The Second Atlas of Breeding Birds in New York State, edited by Kevin J. McGowan and Kimberly Corwin, presents the breeding trends and distributions for the 248 species that currently breed in the state. This atlas is based on data collected over the 2000-2005 breeding seasons. It follows up an atlas published in 1988 using data collected from 1980 to 1985.

For those who may be unfamiliar with breeding atlases, let me pause to give some background. Atlases were first developed in Europe as a way to map breeding distributions. If atlases are repeated, they become useful for measuring changes in bird populations in response to human activity. Many American states and some Canadian provinces have completed at least one atlas and some have now completed a second. A list of North American atlases is available here.

For the purposes of an atlas, a state is divided into rectangular blocks, often subdivided from USGS 7.5-minute quadrangles. (The New York atlas uses 5 km squares instead of the USGS system.) Volunteers search their assigned blocks for potential breeding birds over a five-year period. Species are recorded as breeders based on observed behaviors. For example, if a volunteer sees an Eastern Bluebird carry food into a nestbox, then Eastern Bluebird would be a confirmed breeding species for that block. Meanwhile, the male and female Carolina Wrens singing nearby would be probable breeders in the absence of more concrete evidence of breeding. Even in a relatively small state like New York, completing a breeding bird atlas requires many skilled and dedicated volunteers to achieve complete coverage.

New York is one of the first states to publish a second edition. (For DC-area readers, Maryland completed surveys for a second atlas several years ago, but to my knowledge it is not yet published in book form.) A useful introduction explains the methodology and how to understand the distribution maps. It includes several maps of New York that show regional differences in population, land use, rainfall, average temperature, elevation, and vegetation types. Additional chapters discuss the varied habitats within the state, how land-use changes over the past 400 years have affected breeding birds, ornithology within the state, and current conservation programs.

Species pages comprise the core of the atlas. Each species observed in the state has its own account. On the facing page are maps showing its current breeding range in New York and how that range has changed since the surveys for the original atlas. Many species accounts also include a graph showing its trend according to the Breeding Bird Survey from 1965-2005. A few accounts (most notably owls) include instead a graph of reports from the Christmas Bird Counts over the same period. Species accounts are interspersed with color paintings showing New York habitats with their characteristic bird species. Black-and-white drawings are presented for each breeding bird.

A breeding bird atlas is the place to turn if you want to know the answers to such questions as, "Which Traill's Flycatcher species is more common in the Adirondacks?" or "Where can I find breeding Yellow-crowned Night-Herons?" or "Where can I go to get away from all these starlings?" (And really, what birder doesn't want such information?) Perusing the atlas maps reveals the effects of vegetation type and elevation on bird distributions. Many species found elsewhere in the state virtually disappear in the Adirondack region. (An example of this effect is shown at right.) A smaller set of species, such as Swainson's Thrush (see above), are found only in the Adirondack and Catskill highlands. A few species, such as Double-crested Cormorant, are concentrated along major waterways.

This edition of the atlas is most interesting for what it can tell us about changing bird distributions in New York state. Each species account discusses changes since the last atlas, and compares them to continent-wide trends. Eleven species are new to the second atlas, while five species from the first atlas were not observed for the second. The authors found some hints of climate change in the data from New York: 27% of southerly species shifted northward, while 30% of northerly species saw the southern boundary of their range move north. The best examples of this phenomenon may be the Red-bellied Woodpecker and Tufted Titmouse, both of whose populations have expanded remarkably in New York in recent years. However, that the geographical features of New York state make it difficult to draw strong conclusions from this data.

This is the best breeding bird atlas that I have yet seen. I highly recommend it to anyone interested in the birds of New York state, and to anyone interested in population trends of birds in the northeastern United States. This volume should be of special interest to birders who live in or visit the state regularly.

The Second Atlas of Breeding Birds in New York State, edited by Kevin J. McGowan and Kimberly Corwin. Ithaca, NY: Cornell University Press, 2008. Pp. xxii, 688; black-and-white and color illustrations, maps, tables, graphs, appendices, bibliography, index. $59.95 cloth.

To learn more about breeding bird atlases, see: