Breeding Bird Atlases
A Chance for Birders to Make an Important Contribution
William E. Davis, Jr.*

*Division of Science and Mathematics, College of General Studies,
Boston University, 871 Commonwealth Avenue, Boston, Massachusetts 02215

published in Birding June 1997

In the beginning...

Maps showing the geographic distributions of bird species date back to the early part of this century and have become a standard feature of field guides, state and provincial bird books, and monographs on birds. These distribution maps are generally based on published information and nest record compilations. Grid-based atlases (bound maps usually supplemented with text) are a more recent invention and have proliferated into a broad spectrum of projects and publications with an equally broad spectrum of goals.

The pioneering grid-based atlasing projects began in Great Britain in the 1950s with a botanical atlas that prompted a pilot project on mapping the breeding bird distribution of England's West Midlands. This in turn led to a broader project culminating in the publication of the Atlas of Breeding Birds in Britain and Ireland (Sharrock 1976). The European Ornithological Atlas Committee was established in 1971, and a flurry of activity on the continent resulted in the publication of similar atlases in Denmark, France, West Germany, the Netherlands, and Switzerland by 1980, as well as several covering more restricted geographic areas. These atlases were based on 5-kilometer (km) or 10-km per-side grid squares that provide small enough scale to make even fairly small changes in distribution of birds apparent in the future. These atlases differ from previous bird distribution atlases in representing a "snap-shot" in time, all-be-it a snap-shot with a usual exposure time of five years, rather than a compilation of historical records, and in the use of virtual armies of birders to provide the database from which the atlases are compiled. These atlases provide a baseline of known distributions against which future snap-shots can be compared. The atlasing fever rapidly spread world-wide, and atlases, at a variety of scales have been published in Africa, Australia, Europe, New Zealand, and North America (Robbins 1982).

In North America, the first grid-based atlas projects to reach fruition began when several western states, including Montana and Colorado, compiled bird distribution atlases, but these relied heavily on existing information, and their scale was large--the compilers used a grid system in which each "block" (the basic geographical unit in which data are gathered, presented, and analyzed) was one degree of latitude by one degree of longitude (a "latilong"). Most recent atlasing projects have used approximately 5-kilometer square blocks, of which approximately 400 fit a one degree latilong block! Hence some people argue that their large scale and lack of time constraints make it difficult for latilong atlases to perform one of the major functions of a breeding bird atlas--to monitor changes in distribution and abundance through time. At the latilong scale there would have to be a catastrophic plummet in a species' numbers and distribution for such a change to be observed in subsequent atlasing efforts. The rather unique grid-based atlas, Breeding Birds of North Dakota (Stewart 1975), was the product of an extended, largely one-man project, in which the grid block was the township (six miles per side). It was based primarily on field work from 1961-1970, but historical records from a variety of sources were included. The breeding status of a species is generally ranked as "observed," "possible", "probable", or "confirmed", with criteria--often hotly debated and not uniformly used--for each category. For example, if an individual bird is seen in a block during the breeding season but not in suitable breeding habitat, it is listed as observed; if in suitable habitat it is listed as possible. A pair of birds in suitable breeding habitat would be listed as probable, and a nest with eggs or young as confirmed.

The "true" atlas projects begin

North American atlas projects based on small-scale grids began in Maryland in the 1970s where a county-by-county project was started. The first publication of results was The Breeding Bird Atlas of Montgomery and Howard Counties, Maryland which appeared in the local bird journal Maryland Birdlife (Klimkiewicz and Solem 1978). This was a harbinger. With it began a deluge of county, regional, province, and state publications that continue to pour across the counters of book dealers.

In 1980 the North American Ornithological Atlas Committee (NORAC) was organized, and in 1981 a Northeastern Breeding Bird Atlas Conference was held at the Vermont Institute of Natural Science in Woodstock, Vermont. The outcome was a published Proceedings volume (Laughlin 1982) loaded with informative papers including an overview of international atlasing by Chandler S. Robbins, a major contributor to the initiation of atlasing projects in North America. A second conference and Proceedings followed in 1986, sponsored by the Cornell Laboratory of Ornithology in Ithaca, New York (Sutcliffe et al. 1986). This burst of activity led to the publication of several major papers on atlasing breeding birds (e.g., Udvardy 1981, Laughlin et al. 1982, Butcher and Smith 1986), and eventually NORAC published Handbook for Atlasing American Breeding Birds in English and Spanish editions (Smith 1990). It was reported at the 1986 conference that more than 30 states and provinces had atlas projects under way. After periods of data collection, which usually involved approximately five or six (often an "extra" year is added) years, the long, expensive, and often painful process of compilation and publication of the results was undertaken. This process has resulted in the production a wide variety of formats, styles, and supplemental information. Some atlases have been hardback, some soft cover, some contain species accounts, some are copiously illustrated, and some have fancy supplemental materials such as overlay transparencies that facilitate comparing breeding bird distribution with a variety of habitat and climatic phenomena. A few examples here (Not included here) of this broad spectrum of publications show the diversity of format and project design, and illustrate the problems, strengths, and weaknesses inherent in atlasing projects.

Atlas projects reach fruition

The Atlas of Breeding Birds of Vermont (Laughlin and Kibbe 1985) was the first state or provincial atlas published in North America. It became a model for many other atlases and typifies many of the positive aspects and pitfalls common to atlas projects. The grid scale chosen was approximately 5-km per-side blocks that were established by subdividing a standard U.S. Geological Survey (U.S.G.S.) 7.5-minute quadrangle map into six blocks. Because of a shortage of manpower (a chronic problem in atlasing projects) only one block (a randomly selected "priority block") per quadrangle was targeted for intensive coverage, although information for the other blocks was accepted when available. In addition, 24 blocks containing "unique and fragile habitat" were also targeted for intensive coverage. Six years of data collection (1976-1981) were used to construct a map for each species, showing by the size of dots the location of blocks where the species was a possible, probable, or confirmed breeder.

A species account for each confirmed breeding species was printed on facing pages with a pen-and-ink drawing of the bird and the distribution map. Possible and probable breeding species had smaller maps and shorter natural history accounts. Also included were eight plastic overlay maps that facilitate comparison of a species' breeding distribution with physiographic regions, county boundaries, elevations, agricultural lands, precipitation, and July temperatures. This excellent hardback book also illustrated some of the major problems inherent in most atlasing projects. Perhaps the most serious problem is a lack of information on species abundance. A block with one breeding pair cannot be distinguished from a block with 1000 pairs. The usual biases involving detection of rare, secretive, or nocturnal birds and early nesting species, uneven coverage of priority blocks, and differences in observer experience and ability are discussed and cautionary pronouncements included. All things considered, this is an excellent and landmark book.

The New York state atlasing project, and its publication The Atlas of Breeding Birds in New York State (Andrle and Carroll 1988), was a daunting project. More than 4300 volunteers contributed more than 200,000 hours in the field. There was at least some field coverage for nearly all of the 5335 25-km2 blocks! About a quarter of the blocks were visited by "block busting" teams consisting of two people who spent a day (and night) in each block "busted". The grid differed from most state projects in that a metric-based system was employed rather than subdivisions of U.S Geological Survey maps. This system, the New York Transverse Mercator Grid, divided the state into 5-km per-side squares. Species accounts together with a drawing of the bird occupy a single page of text (often less) and present historical information about distribution as well as breeding biology information. The distribution map is on the facing page. The maps are large and each block where the species was observed is pictured with a solid black square if breeding was confirmed, or other symbols for possible or probable nesting. Maps depicting vegetation, elevation, etc. are included, and plastic overlays of most of these features are available at extra cost. The latter are helpful because the species maps are, of necessity, virtually featureless. The drawings occupy nearly a quarter of the text page but are generally excellent in quality. Appendices describe the ecological zones of the state (e.g., Appalachian Plateau), natural and cultural (e.g., mosquito ditch) ecological communities, and tables of breeding-season data (e.g., egg dates) for each species. The book is wider than it is tall (landscape format), presumably an adaptation for the shape of New York state. Like most of the published atlases there is an attempt to provide a great deal more information about the birds than just what is depicted in the distribution maps.

The Atlas of Breeding Birds of Michigan (Brewer et al. 1991) is a large (8.5 x 11 inches), handsome book, that employs the same basic design for species accounts as the New York atlas. The species distribution maps are large and easy to read, with large blue squares representing confirmed breeding, circles probable breeding, and tiny squares possible breeding. The grid base is, however, the 36-square-mile township, each of which is subdivided into four 9-square-mile blocks. All the blocks in the lower half of Michigan's Lower Peninsula received coverage, but only two blocks out of four received coverage in the northern half, and one block per township in the Upper Peninsula. This "stratified sampling" effort resulted from a number of considerations including uniformity of habitat and concentration of volunteers, and resulted in a total of 4301 "priority blocks" targeted for intensive coverage. To the usual biases was added the inclusion of gamebird and raptor data from other studies. The book includes a chapter on land, climate, and vegetation, supplemented with maps including fascinating ones depicting presettlement vegetation and current vegetation, a chapter on the pre-European settlement avifauna, an analysis of post-settlement changes, and chapters on biogeography and ecology and conservation perspectives. The distribution maps are supplemented when feasible with small abundance maps from the National Biological Service's Breeding Bird Survey data, which attempt to address the census data deficiency common to most atlas projects. As with most state and provincial atlases, the references section is a veritable gold mine of information about local birds, much of it tucked away in local bird journals. This book is much, much more than a compendium of maps.

Atlas of Breeding Birds in Pennsylvania (Brauning 1992) is another attractive and informative atlas. This project, as have most in the United States, used the U.S.G.S. topographic maps of 7.5 minutes of latitude and longitude subdivided into six blocks. The coverage was interesting, however, in that the southeastern block in each quadrangle was designated as a priority block, but coverage was targeted for all blocks. This priority block system provided initial intense coverage for one block that could subsequently act as a measure of quality control for the other five blocks during the seven years of field work. In this very ambitious project all 4928 blocks received some coverage and produced nearly 32,000 records. The book contains a brief history of atlasing projects and a history of Pennsylvania ornithology, along with the obligatory methods section, and is augmented by eight plastic overlays.

The Atlas of Breeding Birds in Rhode Island (1982-1987) (Enser 1992) and Atlas of Breeding Birds in Maine, 1978-1983 (Adamus n.d.) are examples of atlases compiled and published on a low budget. The Rhode Island atlas presents one species per page, with a short paragraph of text at most, whereas the Maine atlas has no species accounts accompanying the distribution maps, but in many cases provides short annotations and references. The latter has a useful bibliography of Maine ornithology published since 1949, and it presents all of the atlas data in tabular form, which would be useful for some retrieval purposes. The Maine atlas differs from those of most eastern states in using a larger scale with blocks consisting of entire U.S.G.S. 7.5-minute quadrangles.

Remarkably comprehensive atlases, full of ecological information, have been produced for several counties in California (e.g., Marin County [Shuford 1993]) and more than a dozen county projects are underway or complete in California alone. Atlas of the Breeding Birds of Monterey County (Roberson and Tenney 1993) used a priority block system to accommodate a limited supply of volunteers for a large area (Monterey County is larger than the state of Rhode Island). One interesting feature of this atlas is the inclusion of abundance estimates based on an exponential scale of 1 pair only, 2-10, 11-100, or 101-1000 pairs. These data provide very rough population estimates for the county. How useful these estimates are is the subject of some debate, but it represents an attempt to correct one of the main deficiencies in most atlasing projects. For many species two maps are presented, one showing recorded breeding categories of confirmed, probable, and possible, and the other showing abundance estimates. Population estimates for many species are included in the text of the species accounts. This is a beautifully illustrated and comprehensive book.

Another county atlas of note is the Atlas of the Breeding Birds of Los Alamos County, New Mexico (Travis 1992). Los Alamos County is small (111 square miles), and each of the sixty 2,5-km- per-side blocks received coverage during the five years of field work. Interesting features of this atlas include tables of bird species/habitat associations (e.g., 21 species are associated with pinyon/juniper woodlands), and numerous other ecological analyses.

The Canadians have done a remarkable job in producing high- quality atlases under the difficult circumstances of vast regions with sparse population and difficult or limited access. The Ontario atlas project used 10-kilometer-per-side blocks for the more populated southern section but 100-km-per-side blocks for the sparsely settled northern regions of the province. The final product, Atlas of the Breeding Birds of Ontario (Cadman et al. 1987) was the first of the Canadian projects to be published. The atlas includes histograms of abundance estimates along with the usual breeding distribution maps. Unfortunately the confirmed, probable, and possible categories were represented on the maps with squares of three intensities of the same color, which make them hard to distinguish.

In Alberta, where there are more than 6000 10-km-per-side squares, one of every block of four squares was designated a priority block in southern portions of the province and one out of 100 for remote northern areas. Atlasers were encouraged to organize "square bashing parties" in order to achieve the desired coverage. The project received more than 40,000 hours of field work from nearly a thousand atlasers. The final product, The Atlas of Breeding Birds of Alberta (Semenchuk 1993), is large (9 x 12 inches) and beautifully illustrated with color photographs of each species and distribution maps with colored backgrounds showing the natural regions (e.g., boreal forest, grasslands), making it a truly elegant book. Other excellent provincial atlases include those for the Maritime Provinces (Erskine 1992) and most recently Quebec (Cyr 1995).

What does the future hold?

Atlasing projects continue to come to fruition in the United States. The atlas for Ohio appeared in 1991 (Peterjohn and Rice) but is already out of print. This atlas featured a priority block system supplemented by "special areas", including unique or localized habitats such as hemlock ravine and wetlands.

In 1994 atlases for West Virginia (Buckelew and Hall), Connecticut (Bevier), and New Hampshire (Foss) were published. The West Virginia atlas presented one species per page but included seven plastic overlays of useful features such as percentage of forest cover, annual precipitation, and topographic features. The Connecticut atlas was published in landscape format with each species account occupying two (facing) pages with a map and line drawing for each species. It also has an interesting eleven page section on interpreting distributions of breeding birds. The New Hampshire atlas is a large and handsome book with huge, easily read maps, and extensive text for each species.

In 1995 the atlas for South Dakota (Peterson) appeared and in 1996 the atlas for Kentucky (Palmer-Ball). The former features a spiral wire binding with large maps with information presented in tabular form on habitat element types (e.g., natural, manmade), early and late dates, and abundance estimates. Each species is covered in a single page with text restricted to a few sentences. The Kentucky atlas presents separate maps for breeding status and abundance, and includes a photograph of every species. It also features data analysis by physiographic province and a tabular summary of each species' breeding status.

Several other publications are expected shortly (e.g., for Colorado, Delaware, Iowa, Maryland and the District of Columbia, New Jersey, Saskatchewan, Tennessee, and Virginia).

Publication of atlasing results often takes years after the completion of the atlas field work. The most extreme example of this is the atlas for Massachusetts. This was the first state-wide project to be implemented, with field work conducted from 1974-1979. A variety of problems and some indecision concerning publishing a separate atlas or including the maps with the recently published Birds of Massachusetts (Veit and Peterson 1993) led to a series of delays. Publication is currently scheduled for 1996 or 1997. Interestingly, from a strictly scientific point of view it really does not matter when an atlas gets published, as long as it gets published, because it represents a datum plane of breeding bird distribution. The data never become obsolete and are as valid and important 25 years after they were collected as they were at the time of collection. In addition, the data from atlas projects are often available long before they are published in atlas form. For example, in the Maryland atlas project, the data were entered into computers each year and made available for land management decisions by state and county agencies (C. Robbins, pers. comm.). The burgeoning technologies of Internet and cyberspace will surely further facilitate public access to atlas data in the future.

Atlas projects that quantify breeding bird distribution in North America have provided, and continue to provide, birders with an increasingly important role in scientific ornithology and in habitat and avian conservation. Birders have contributed literally hundreds of thousands of hours to atlasing projects in the past two decades. The importance of these projects continues to grow. They provide detailed information on the distribution of breeding birds for birders wishing to see them. But they accomplish much more than that. They provide quantitative information for land managers and conservationists that can be used to make informed land management decisions, including critical habitat assessment, setting priorities for land acquisition, and assessing the effects of habitat fragmentation. Quantitative information on breeding birds can be powerful ammunition in a conservation organization's arsenal when critical habitat is threatened by development or funds need to be raised for land acquisition. When you become involved with an atlasing project you are contributing to a long-term project the value of which will increase as future snap-shots-in-time make possible assessment of population trends and a broad spectrum of other ecological perspectives. In Europe, the first of the second generation snapshots has already been taken. The New Atlas of Breeding Birds in Britain and Ireland: 1988-1991 (Gibbons et al. 1993) is the first of the second generation atlases to be published. For each species it includes maps depicting abundance, distribution, and status changes that have occurred in the twenty years since the first generation atlas was published.

Participation in atlasing projects provides an opportunity for those for whom birding is primarily a recreational pastime to make important contributions to scientific ornithology and conservation initiatives. And it's fun! If your state or province has already completed its first round of atlasing, why not try another state--most atlasing projects would welcome help, including "block busting." And some states and provinces are nearing the time when the second round of atlasing is about to begin.


I thank Sarah B. Laughlin, Wayne R. Petersen, Chandler S. Robbins, and Charles R. Smith for their helpful suggestions on previous drafts of the manuscript.


Adamus, P. R. n.d. Atlas of Breeding Birds in Maine, 1978-1983. Maine Department of Inland Fisheries and Wildlife, Augusta.

Andrle, R. F., and J. R. Carroll. 1988. The Atlas of Breeding Birds in New York State. Cornell University Press, Ithaca.

Bevier, L. R. 1994. The Atlas of Breeding Birds of Connecticut. Bulletin 113, State Geological and Natural History Survey of Connecticut, Hartford.

Brauning, D. W. 1992. Atlas of Breeding Birds in Pennsylvania. University of Pittsburgh Press, Pittsburgh.

Brewer, R., G. A. McPeek, and R. J. Adams, Jr. 1991. The Atlas of Breeding Birds of Michigan. Michigan State University Press, East Lansing.

Buckelew, A. R., Jr., and G. A. Hall. 1994. The West Virginia Breeding Bird Atlas. University of Pittsburgh Press, Pittsburgh.

Butcher, G. S., and C. R. Smith. 1986. Breeding bird atlases add zip to summer birding. American Birds 40: 419-428.

Cadman, D., P. F. J. Eagles, and F. M. Helleiner. 1987. Atlas of Breeding Birds of Ontario. University of Waterloo Press, Waterloo.

Cyr, A., and J. Larivee. 1995. Atlas Saisonnier des Oieaux du Quebec. Presses de l'Universite de Sherbrooke and Societe de Loisir Ornithologique de l'Estrie, Inc., Sherbrooke.

Enser, R. W. 1992. The Atlas of Breeding Birds in Rhode Island. Rhode Island Department of Environmental Management.

Erskine, A. J. 1992. Atlas of Breeding Birds of the Maritime Provinces. Nova Scotia Museum, Halifax.

Foss, C. R. 1994. Atlas of Breeding Birds in New Hampshire. Audubon Society of New Hampshire, Dover.

Gibbons, D. W., J. B. Reid, and R. A. Chapman. 1993. The New Atlas of Breeding Birds in Britain and Ireland: 1988-1991. T & AD Poyser, London.

Klimkiewicz, M. K., and J. K. Solem. 1979. The breeding bird atlas of Montgomery and Howard Counties, Maryland. Maryland Birdlife 34: 3-39.

Laughlin, S. B. 1982. Proceedings of the Northeastern Breeding Bird Atlas Conference. Vermont Institute of Natural Science, Woodstock.

Laughlin, S. B., and D. P. Kibbe. 1985. The Atlas of Breeding Birds of Vermont. University Press of New England, Hanover, for the Vermont Institute of Natural Science.

Laughlin, S. B., D. P. Kibbe, and P. F. J. Eagles. 1982. Atlasing the distribution of the breeding birds of North America. American Birds 36: 6-19.

Palmer-Ball, B. L., Jr. 1996. The Kentucky Breeding Bird Atlas. University of Kentucky Press, Lexington.

Peterjohn, B. G., and D. L. Rice. 1991. The Ohio Breeding Bird Atlas. Ohio Department of Natural Resources, Columbus.

Peterson, R. A. 1995. The South Dakota Breeding Bird Atlas. South Dakota Ornithologists' Union, Aberdeen.

Robbins, C. S. 1982. Overview of international atlasing. In S. B. Laughlin (ed.). Proceedings of the Northeastern Breeding Bird Atlas Conference. Vermont Institute of Natural Science, Woodstock.

Roberson, D., and C. Tenney. 1993. Atlas of the Breeding Birds of Monterey County California. Monterey Peninsula Audubon Society, Monterey.

Semenchuk, G. P. 1992. The Atlas of Breeding Birds of Alberta. Federation of Alberta Naturalists, Edmonton.

Sharrock, J. T. R. 1976. The Atlas of Breeding Birds in Britian and Ireland. T & A. D. Poyser, Calton, England.

Smith, C. R. 1990. Handbook for Atlasing North American Breeding Birds. Vermont Institute of Natural Science, Woodstock, for the North American Ornithological Atlas Committee.

Shuford, W. D. 1993. The Marin County Breeding Bird Atlas. Bushtit Books, Bolinas, California.

Stewart, R. E. 1975. Breeding Birds of North Dakota. Tri-College Center for Environmental Studies, Fargo.

Sutcliffe, S. M., R. E. Bonney, and J. D. Lowe. 1986. Proceedings of the Northeastern Breeding Bird Atlas Conference. Cornell Laboratory of Ornithology, Ithaca.

Travis, J. R. 1992. Atlas of Breeding Birds of Los Alamos County, New Mexico. Los Alamos National Laboratory, Los Alamos.

Udvardy, M. D. F. 1981. An overview of grid-based atlas works in ornithology. In: Studies in Avian Biology No. 6:103-109.

Veit, R., and W. Petersen. 1993. Birds of Massachusetts. Massachusetts Audubon Society, Lincoln.

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