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Thirty years of breeding bird survey in North America

Chandler S. Robbins

The North American Breeding Bird Survey (BBS) stands as a tribute to the dedication of tens of thousands of experienced amateur birders throughout the United States and Canada. Each participant is assigned one or more roadside routes whose starting point (latitude and longitude) and direction have been determined from a table of random numbers. Each survey route consists of 50 three-minute stops at half-mile (800 m) intervals along secondary roads. Observers are given maps of the routes and stops and printed forms with names of the birds most likely to be found along each particular route. Counts may be taken on any day in June, or a week earlier in the south or a week later in Canada, as long as weather conditions are favorable-meaning wind less than Beaufort 3 (8-12 mph) and no rain. Participants may have an additional person as driver or record keeper, but the count must be made by only the official observer. The program is administered in Canada by the Canadian Wildlife Service and in the U.S. by the Biological Resources Division, U.S. Geological Survey (formerly by the U.S. Fish and Wildlife Service).

About 2900 of the 3700 active survey routes (see figure) are surveyed annually. Each is covered only once per season, and coverage begins at exactly one-half hour before local sunrise. The starting time is indicated on the unique printed bird list for each route. Observers count not only the number of species detected during the three minutes at each stop, but also the number they can detect of each species. Birds observed between stops are not counted.

History

The BBS was begun during the DDT era in response to concern over declining songbird populations. At that time no data base existed for tracking population changes either regionally or continentally. Methodology was field tested in Maryland and New Hampshire during the 1964 breeding season, and in 1965 volunteers from the Maryland and Delmarva Ornithological Societies successfully surveyed all 50 random routes in Maryland and all ten in Delaware. In this initial venture, each participant completed a 50-stop Check Route in addition to his or her primary assigned route. The Check Routes were BBS routes that I also covered that same year, and their purpose was to check each observer's results for comparability. A few observers were disqualified and their routes assigned to other volunteers. In 1966 the BBS was expanded to include all states and provinces east of the Mississippi River. The next year the coverage was expanded westward to the base of the Rocky Mountains, and in 1968 the entire continent was included.

Limitations

The BBS was designed to monitor trends in common species. Threatened and endangered species are not found in large enough numbers to be monitored along random transects. Likewise, nocturnal species, colonial nesting species, and birds found primarily in habitats not sampled by roadsides are not adequately sampled. Even for species that are well sampled along roadsides, population trends along roads may not be the same as trends away from roads. For example, in a developed neighborhood, roadside habitat change may be minimal and bird populations stable; yet a half-mile away, habitat changes and bird population changes may be considerable. Also, amenity strips of undisturbed forest may be left along a road to conceal clearcuts or other habitat changes from a roadside observer. Studies currently underway will give some insight into roadside bias.

Trend Analysis

Trend estimates are calculated for about 500 species of North American birds at the state/province and regional level and also by physiographic regions. The basic unit of analysis is the mean number of birds within a physiographic region within a state or province, but over the years the analysis has become more sophisticated, giving additional weight to regions of greater abundance and compensating for observer changes. Field procedures, however, remain unchanged. Trend estimates for any species for any state or province, physiographic or geographical region, and any specified period of years may be obtained from the USGS Patuxent Wildlife Research Center at http://www.mbr-pwrc.usgs.gov/bbs/. This makes it easy to follow effects of weather events such as prolonged cold or excessive rain. Full potential of survey results to track effects of habitat change is still to be realized.

The 30-year history of the BBS has brought many bird population changes to public attention (Robbins et al. 1986, 1989; Sauer et al. 1999). For example, the BBS has documented rapid decline in Red-headed Woodpeckers in the Mississippi Valley and in Florida; decline of the Prairie Warbler in the southeast; and spread of the House Finch in the east following its release on Long Island. Relative abundance maps (see figure), also available on the web site, help put the trend maps in perspective. I anticipate that analysis techniques will increase in sophistication and that use of this resource for conservation planning will increase dramatically in coming decades.

Literature Cited

Robbins, C. S., D. Bystrak, and P. H. Geissler. 1986. The breeding bird survey: its first fifteen years, 1965-1979. U.S. Fish and Wildlife Service Resource Publications 157.

Robbins, C. S., J. R. Sauer, R. S. Greenberg, and S. Droege. 1989. Population declines in North American birds that migrate to the neotropics. Proceedings of the National Academy of Sciences. USA 86:7658-7662.

Sauer, J. R., J. E. Hines, I. Thomas, J. Fallon, and G. Gough. 1999. The North American breeding bird survey, results and analysis 1966-1998, Version 1998.1. USGS Patuxent Wildlife Research Center, Laurel, Maryland.

Chandler S. Robbins received the 1999 Edward T. LaRoe III Memorial Award from the Society for Conservation Biology in recognition of his leadership in translating principles of conservation biology into real-world conservation.

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